»} ll b D HABITAT USE AND ENERGETICS OF AMERICAN BLACK DUCKS WINTERING AT CHINCOTEAGUE, VIRGINIA bv John M. Morton Thesis submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fultillment of the requirements for the degree of MASTER OF SCIENCE in Flsheries and Wildlife Sciences . APPRO)/ED: - I [I Il I/{ Nv 1, - „ ~«/ r. R y L? rkpatl Tk, Chairman 1 Q - / ·’ . l . ‘ ‘) / F 4 Dr. Michael R. Vaughan Q) . Öqr. Dean F. Stäfér I 12 May 1987 Blacksburg, Virginia
158
Embed
b D - vtechworks.lib.vt.edu D HABITAT USE AND ENERGETICS OF AMERICAN BLACK DUCKS WINTERING AT CHINCOTEAGUE, ... Sarcosporidiosis ..... 102 Discussion ...
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
»} llb D
HABITAT USE AND ENERGETICS OF AMERICAN BLACK DUCKS WINTERING
AT CHINCOTEAGUE, VIRGINIA
bv
John M. Morton
Thesis submitted to the Faculty of the
Virginia Polytechnic Institute and State University
in partial fultillment of the requirements for the degree of
MASTER OF SCIENCE
in
Flsheries and Wildlife Sciences
. APPRO)/ED:
- I [I Il I/{Nv
1,-
„ ~«/
r. R y L? rkpatl Tk, Chairman1 Q
- /·’
.l .
‘
‘)/ F 4
Dr. Michael R. Vaughan Q).
Öqr. Dean F. StäférI
12 May 1987
Blacksburg, Virginia
35T
HABITAT USE AND ENERGETICS OF AMERICAN BLACK DUCKS WINTERING
{ AT CHINCOTEAGUE, VIRGINIAJ by
John M. Morton
Dr. Roy L. Kirkpatrick, Chairman
Fisheries and Wildlife Sciences
(ABSTRACT)
The habitat use and energetlcs of American black ducks (Anas rubripes) wintering at
Chincoteague National Wildlife Refuge, Virginia, were investigated. Twenty-two female black
ducks were systematically radiotracked on the 25,600 ha study area between 15 December
1985 and 28 February 1986. Diurnal time and energy budgets were constructed by distributing
1,471 scans (collected in 1985-86 and 1986-87) over a time-tide matrix within refuge, saltmarsh,
and tidal water habitats. Sixty-four ducks were collected during early, mid, and late winter in
1985-86 to determine changes in carcass composition. The Habitat Suitability index (HSI)
model for wintering black ducks was evaluated. Age affected range and core areas but did
not affect habitat selection. Tide, ice, and time of day affected habitat use. Refuge pools were
used during the day and saltmarsh was used at night. Subtidal water was used during periods
of icing. Black ducks fed least and rested most when in refuge pools but fed most and rested
least when in tidal waters. Black ducks curtailed feeding and increased time spent in alert
and locomotion behaviors in response to disturbance. Whole carcass analysis indicated that
black ducks were at least as fat and heavy in the spring as they were in the fall. Comparisons
with similar work in Maine suggested that black ducks wintering in Maine and Virginia expend
the same energy at a given temperature. However, because of lower temperatures, black
ducks collected at Chincoteague were in relatively better condition than ducks wintering in
Maine.
Acknowledgements
I wish to thank my advisor, Dr. Roy L. Kirkpatrick, for creating a sincere and stimulating
working environment, as well as his support and friendship during my graduate studies. I also
wish to e><tend my gratitude to my other committee members, Drs. Michael R. Vaughan and
Dean F. Stauffer, for their constructive comments throughout this study.
Table 9. Effect of ice cover on use of three habitats. ........................... 43
Table 10. Effect of ice cover on use of saltmarsh. .............................. 44
Table 11. Comparison of telemetry and aerial survey techniques. ................. 45
Table 12. Diurnal and nocturnal use of refuge and nonrefuge habitats. .............. 46
Table 13. Correlations of behaviors with weather and other variables. .............. 75
Table 14. Effects of habitat, time, and tide on behaviors. ......................... 76
Table 15. Diurnal time budgets. ........................................... 77
Table 16. Diurnal energy expenditure. ...................................... 78
Table 17. Proportional use of three habitats during day and night. ................. 79
Table 18. Nocturnal time budget. .......................................... 80
Table 19. Behavioral responses to human and natural dislurbance. ................ 81
Table 20. lnterspecitic and intraspecitic agonistic encounters. .................... 82
Table 21. Diurnal time budgets of black ducks wintering in Maine and Virginia. ....... 83
List 61 Tables x
Table 22. Pearson correlation matrix of carcass components. ................... 114
Table 23. Effects of age, time, and time on carcass composition. ................. 115
Table 24. Means of body components during early, mid, and late winter. ........... 116
Table 25. Means of fat, protein, water, and ash during early, mid, and late winter. .... 117
Table 26. Correlations of external measurements with selected carcass components. . 118
Table 27. Partial correlations of body weight and structure regressed on fat and the lipidindex. ...................................................... 119
Table 28. Models of weight, water, and weight·structure ratios regressed on lipid index. 120
Table 29. Means of carcass components by sex and age. ....................... 121
U.S. Fish and Wildlife Service, Newton Corner, Massachusetts. 300pp.
Stotts, V.D. 1958. The time of pair formation in black ducks. Trans. N. Am. Wildl. Nat. Re-
source Conf. 23:192-197.
Stotts, V.D. and D.E. Davis. 1960. The black duck in the Chesapeake Bay of Maryland:
breeding behavior and biology. Chesapeake Sci. 1:127-154.
U.S. Fish and Wildlife Service. 1986a. North American waterfowl management plan. A strat-
egy for cooperation. 33pp.
U.S. Fish and Wildlife Service. 1986b. Concept plan for preservation of black duck wintering
habitat. Atlantic coast. U.S. FWS, U.S. Dept. Interior, Newton Corner, MA.
34pp+appendices.
Wooley, J.B., Jr. and R.B. Owen, Jr. 1977. Metabolic rates and heart rate-metabolism re-
Iationships in the black duck (Anas rubripes). Comp. Biochem. Physiol. 57A:363·367.
Wooley, J.B., Jr. and R.B. Owen, Jr. 1978. Energy costs of activity and daily energy expendi-
ture in the black duck. J. Wildl. Manage. 42:739-745.
Habltat use and Movement: 34
Table 1. Available macre-habltat types on the Chlnceteague study area.
HABITAT HECTARES PERCENT
UpIand‘ 6562.0‘ 25.6
Open water' 5518.3 21.5
Subtidal water 5385.5l
21.0
Saltmarsh 4743.1 18.5
Tidal flat 1400.2 5.5
Impoundment 910.0 3.6
Natural pool 423.4 1.7 _
Shrub wetland 324.2 1.2
Stream 304.4 1.2
olneé 42.6 0.2
Total 25614.9 100.0
"Upland includes developed areas and all other areas designated as up-Iand under the National Wetland Inventory classification.
*Open water is 21m deep at mean low tide; subtidal water ls <1m deep '
at mean low tide. Data from 1:24000 USGS topographic maps.
’Other includes those areas designated as dunes under the NationalWetland Inventory classification.
ss
Table 2. Status (as of 4 May 1986) of the 23' radloed female black ducks known to have usedthe Chincoteague study area.
4151 AHY* last located 2/28/86 on study area
4999 AHY alive on study area
5067 AHY dead; post·hunting cripple 1/28/86
5088 HY alive on study area
5112 HY dead; hunter kill 12/18/85
5128 HY alive on study area
5143 HY dead; natural mortality 1/14/86
. 5155 _ AHY last located 1/23/86 on study area
5183 HY alive on study area‘ 5205 HY alive on study area
5231 AHY last located 4/19/86 on study area
5324 HY alive on study area
5336 AHY alive on study area .
5419 AHY last located 1/29/86 on study area; 2/16/86 at Cedar island, VA
5464l
AHY last located 1/23/86 on study area; 2/15/86 at Snowhill, MD
5514 AHY dead; hunter kill 12/30/85
5536 HY last located 4/20/86 on study area
5662 HY never located on study area after release; 2/17/86 at Back Bay NWR, NC
5670 AHY last located 4/6/86 on study area
5767 HY last located 1/8/86 on study area ·
5886 HY alive on study area .
5919 HY last located 12/30/86 on study area; 1/16/86 at Bow Beach, DE
5983 HY last located 4/20/86 on study area
‘lncludes 20 black ducks radio-harnessed at Chincoteague NWR and 3 black ducks (4151, 5536,5670) radio·hamessed at Brigantine NWR, NJ; all were captured and released during De-cember 1985. Radio locations off study area provided by E. Derleth (U.S. Fish and WildlifeService).
'AHY=after hatching year (juvenile); HY=hatching year (adult).
36
ed3Z24;
U!Ö
°°
o
S
NQ
Q
...
E
coQ
QN
R
E
ab
S¤¤N
Y
2
"2
S-
222
§
cu0
O;
Qo
.,.,
3
QQ
Q
o
Ö
Q)
O
OQ
q;
•
ÖQ
:
2-
°<¤
22
,,
•:
cg
oO
2"
··6
4„,
QQ
Q
=_
1*Ö
lX
ä2
3
·••L
•
äg
go
Q
Z
5cn
;Q
Q<·¤
zu
2
·=
1-
QN
N
U‘
mQ
Qc
QE
•-
QQ
Q¤¤
><
uS
•'Q
J
¤.
••€
Q.
éN
Ng
QN
m
N
oaQ
<¤Q
c¤Q
zu
I
cnIn
QY
NQ
_'
>
NQ
Nca
00m
-¤
“’*.9
S2
2
vi¤>
.
ancam
Q
gQ
?'°
gco
„
Ü!
'¤xa
QQ
coQ
MQ
Q-
ae
¤—Q
QQ
co"
Q
‘°
2
*"-
¤¤3
gS
';
.¤
N
cn
§·
-E3
Z
2
3•-
.¤3
gg
a.:
0
EÖ
,_E
D_:
U
1:-¤
Q;-Q
.:
3
·=0
0--
9Q
;·.:
"'
~6
"=
·=
zO
2.2
—1:
ua
ä2
=
:—
°o
·
¤c
¢:°
O"’
QQ
0en
Q
¤>,
c4;
Ücn
Qan
v
>4U
Ü
D
=o
EGJ
g
coo$2
cQ
-
"‘
_;..
Ö..
1-
YQ
Ö
.:
QY
cnÖ
..Q
YO
Q
3:
1-
1-
'·1
-¤
•gu-
„_en
Ö..
QQ
OQ
B
Q
1*
Y.
..N
NIn
<Q
W"
—·S
Qes
§§
.
.ac
ao‘·°
un
‘”~·
OW
eaca
ceQ
eoQ
an
:2
2
§‘§
"*'·*23
§3
2·¤
.¤„„
22
·g2
o5
«.»5
".-
93Q
gQ
Q¤>2
"Q
ZQ
°¤>
cs:
"Q
S
Oeq
InO
ON
QG
,Ql¤
*_m
q
F)
1*
"7N
Q
}
cu3
ca¤
4;¢¤
1-O
cz
_,
LL
Ülc
QQ
l-LE
Q
Q1
-F
V
E
1-
vQ
:¤
cu„.
m
37
Table 4. Mean movement estlmates for luvenile and adult female blackwlntering at Chlncoteague, Vlrglnia, December 1985-February
MOVEMENT' (m)
FREQ AM PM D(
N
Juvenile -
5088 (116)' 982.1 1150.8 346.8 151.1
5128 (118) 1451.2 1525.8 351.4 222.4
5143 (43) 1031.6 1151.0 431.5 289.7
5183 (119) 2239.5 1903.2 828.1 719.7
5205 (121) 4826.2 5722.0 574.6 709.7
5324 (118) 1656.8 1378.7 725.9 858.4
5536 (76) 1847.2 1946.2 556.0 547.9
5767 (35) 5217.3 5103.0 2802.2 1226.3
5886 (115) 1492.0 1867.3 844.2 669.6
5983 (104) 3181.3 3612.8 859.6 600.9
Aßsä ·4151 (86) 585.3 879.2 386.7 555.3
4999 (135) 4642.7 4700.3 356.0 352.3 ·
5067 (28) 1836.8 1667.9 826.7 802.1
5155 (55) 3563.3 3457.7 2197.2 1191.7
5231 (112) 3584.5 3236.6 1400.5 638.9
5336 (119) 2466.5 2713.4 298.3 252.3
5419 (36) 5019.6 4591.5 1464.6 1410.1
5464 (20) 3694.4 4753.6 106.0 296.6
5514 (17) 4934.8 4852.7 597.3 345.8
5670 (65) 582.6 623.4 364.5 50.0
'Movement data averaged over approximately S-hour intervals:AM=crepuscular night-to-day movement, PM =crepuscular day-to-night movement, D=dlurnal movement, N =nocturnal move-ment.
'Number of radio locations used in movement estimates.
38
Table 5. Wllcoxon two·sample comparlson of mean range area, mean corearea, and mean movement estlmates by age class for female black duckswinterlng at Chlncoteague, Virginia, December 1985-February 1986.
Juvenile Adult
7 SE Y SE
Movement‘ (m)
Crepuscular (A.M.) 2392.5 482.2 3091.0 525.9
Crepuscular (P.M.) 2536.1 530.1 3147.6 516.2
Day 832.0 227.6 799.8 213.1
Night 599.6 101.8 589.5 137.1
Range area' (ha)l
50% contour 322.7 68.9 81.8 28.0 "
95% contour 1721.1 458.3 418.6 102.1 '
Core area'‘
core area (ha) 483.2 113.9 183.0 71.5 "
number of cores 1.9 0.5 1.0 0.1 _
‘Movement data for 10 juveniles and 10 adults averaged over approximately6-hour lntervals.
. 'Harmonic mean contours estlmated from 10 juveniles and 10 adults.
’Mean core area based on 10 juveniles and 9 adults; mean number of coresbased on 10 juveniles and 10 adults.
°Asterisk indlcates signlflcant difference between age classes (p S .05).l
39
Table 8. Convex polygon and harmonic mean estlmates of range and core area sizes (ha) forluvenlle and adult lemale black ducks wintering at Chincoteague, Virginia, December1985·February 1988.
’Approx. 500m* cells used in harmonic means procedure to estimate 50% and 95% contours.Harmonic means estimatlon excludes outliers; convex polygon estimatlon includesoutliers.
_ *Statistica| measure of importance of core area; estlmate of the area (expressed as percent
of total range area) that contains the clustered radio locations (expressed as percent oftotal number of locations). Core area estimation excludes outliers. "Asterisk indicates
no statlstical core area ldentitied.
’Number of radio locations used ln range estimation.
40
Table 7. Comparison ol habltat availability to habitat use (uslng Neu’s chi-square statistlc) by female black ducks wlnterlng at Chlncoteague, Virginia,December 1985·February 1986.
Saltmarsh 18.5 49.1 '
Impoundment 3.6·
22.5 '
Subtidal water 21.0 11.5 '
Natural pool 1.7 7.4 '
Tidal flat 5.5 5.9
Shrub 1.2 1.5
Upland 25.6 1.0 ' yStream 1.2 0.8
Open water 21.5 0.3 '
Other 0.2 0.0
‘AlI habitats within 25615 ha study area assumed available.
'Based on 1442 radio locations of 22 birds.
'Asterisk indicates use signiticantly different than availability (p$.05). Overailx'=3145, df=9, p<.001.
I 41
‘Table 8. Comparlson of habltat availability to habltat use' (uslng Johnson’sPreference Assessment Program) by female black ducks wlnterlng atChincoteague, Virglnla, December 1985·February 1986.
HABITAT T BAR' RANK
lmpoundment -3.19a‘ 1
Saltmarsh -2.69al
2
Natural pool -2.11a 3
Shrub -1.81a 4
Stream -1.28a 5
Other -0.94a 6
Tidal tlat -0.17a 7
Subtidal water 0.97a ' 8
Open water 5.14b 9
Upland 6.08b 10
‘Based on individual use of 10 habitats by 18 ducks. Ducks with less than 25radio locations were not used in this analysis.
’Average differences between ranks of use and availability; negative numbersuggests avoidance and positive number suggests preference. °
’Types with same letter are not signllicantly different (p2.0.05) according toWaller-Duncan ranks separation procedure. Overall F=509.5 (df=9,9,p<.01) for H„: all components are equally preferred.
42
6
·‘
¤M
.
¤
N.-
E2
3
Lucu
5.::
Q•«
CO6
.Q
.O§
gC
QQ
U
E2
::2%
UQ
ME
.-
‘䤤
E‘°
EE
IXQ
P3.¤
Q0
._
NE
x.
~c
2¤
c:Ö
Q
•—
Qe
-•
I6
·->‘°
ÜI-
3
E:
0-
ELU
In‘°
'·°ä-S
anCO
M:
äD
·¤
5I-
BN
Uä
gg
*6o
•·=."!
'¤0
.ID
mcu
.:
Fw
3cn
-Q
tl
c
äs-
2¤*
•-·
22
„S"'
.¤¤
lx~·
E‘·°
wg
°3
E°*
ET*6***
Q...
cO
-;-7
6
•¤§
°.
C"
"r-
ES
sth
og
;
¤¤c
SQ
{
c"
gg
·
°«
:
Le
g
LU
N;
0*-
··
>¤
gc
S?
6*;
o2
°o
22
·3-:
SL
:2
•-SE
"
gc
:;
2222
••
L°’,!
¤_•=
Üg
g
E6L!
°2
S==
-0
.:-¤
g°E
°-
:E
I->‘°
*-:
mm
2
Iä
zuE
0*
CD·.
;
43
Ol
GuaEI-2
,E
LU';
N
s2
w=>
52
§
evÖ
·c
22
°6
E
S
—
,„
luQ
Ixtg
It':Q
V!
x
3
QE
c,
=’
8
°ci
'~15
°
E
Ö=¤
Eä
C¤¤
„,§
:2E
"’6
-2
Z
E
_guJ
22
6
w3
•=D
.
1-
E
v
_:
wö
LUnn
ca
gg
__,cn
o¤>
E
2*
6Ö
68
2
‘
*6·~
Ö2
hn
},
lo
¤t¤
rn
mz
E
q;Ix
r—cn
$,,59
Q3
ES
g
=2
°6
2’2
cw-
“
‘
Öä
C•$
-9
”<·=
„E9
26
2‘=
uu
m
..2
°—ä
2.
=ä
..2
2.,
·
ÖE
€Q
ZS.?
gg
2%
vg
ING
aa
.
S
5,,,
.°*
"’¤
og
_:
sv
__
S2
.¤_§N
cu
{E.:
:
<¤
-ä
U.¤
E—
E,.
2E
°ä°92
·
<%§_2
26
U
zumP
44
TABLE 11. Comparison ot telemetry and aerial survey techniques (using Neu's chi-square statlstlc) tor assessing dlumal habitat use of black ducks wintering atChlncoteague, Virginia, Octeber 1985-March 1986.
HABITAT TELEMETRY DATA AERIAL SURVEY DATA
Habitat’ Survey Habitat' Birds/ha Habitat'
Use (%) Count Area (ha)”
Use (%)
Saltmarsh 30.5 ' 6723 1365.3 4.92 13.3
lmpoundments 60.4 14038 617.3 22.74 61.6
Subtidal water 5.2 " 2448 900.5 2.72 7.4
Tidal flat 1.7 ' 768 297.8 2.58 7.0
Open water 0.1 10 207.0 0.05 0.1
Streams 1.5 ' 343 87.2 3.93 10.6
Other 0.7 0 156.1 0.00 0.0
Total 100.1 24330 3631.2 36.94 100.0
'Based on 752 diurnal radio locations of 22 birds. Asterisk indicates frequency derivedfrom telemetry data is signilicantly different (ps.05) than frequency derived fromaerial survey data. x'=289.1, df=6, p<.01.
_
’Area of habitat within survey transect.
°Percent habitat use=((birds/ha)/36.94) x 100; this procedure weights the observedsurvey count by proportional habitat tlown over.
45
·89¤V89E
.
·¤2":
E
,an
q6.
~—o
>>
.¤
O
3J
ä
5
5
-¤Wg""
c>
E
-¤c•O
co
0
ex-·
}-¤
¤.
°z·
;
na
V
ga
1-'D
ÖQ
G
cu.
'_
¤
Tg
I
••°
cg
)
CD
G¤
gn
.sg
¢¤c><I',_,$c>
U
4
·;E
äo
vi
c,J
HQ
vu-Q
C
gu
“°ä
es
0
3%>-
'¤
.:2
<a
m
0
gg
NQ
DQ
C,6
vw
¤_
1.:
vu
nm
md
mv
x
3>
vw
ed
<¤J
ßä
"
§
•¤
O
gß
I.|..I
0
Nu
(B
•¤
„°
D
0
.
No
g_
EE
gg
S
2
uJ
rn·
¤—‘!ä
<°
S"
anZ
3
46
;,
*5
.¤9
-
2;
*5
,_¤
.
-¤"’
n-5
;
NE
·¤
Ü";
gg
°·¤E-
.
mg
»-wb
}-¤
I|
EN
:8
?
46
°Ü‘
*=‘··E
*“*
~'
Um
G
·;_E:
äs
\~zu
EJ
"'Q
J'ya
.,
gw
-ä
g•\
’g·
äBä
/E
U9
‘'
¢
"Ü,
1 1·
ä„
‘1
¤„
_°
1(\
1
-e
sQ
’§\/§
(\•,._
ä
äc
s,\*
§mz
ärg
"‘E
‘
IL
47
Aum-es x cnounu sunvsv ——-
;_1965·66 GROUND SURVEY
1965-66 ÄERIAL SURVEY ·-·•··•·•·A
<¤ E 2 2 2Q ° 2 2 =
1500gä§
E E Egg F E 2w E l' . 2m E E EE : j =· :=
1000 E'_,• •
EZ 5 5 ,.,E { Ä ··
•,·~•• .
=·· E 2
s30SEP 14 NOV 29 DEC 12 FEB 29 MAR
· DATE'
Flgure 2. Ground and aerlal counts of black duck: ln the Chlncoteague NatlonalWildlife Refuge.
A48
·
E
.V
°z
W=
.,E
5E.
5
¢S
uQ
E
ääh
Sug
0
•-•Q
U
40
\_
Q•-•
4:1
„\q
.
•·
sc·¤
‘z
rn
E
8
7**U
-l
.10
W
\¤
1-
E4
Q:
a:
.¤
.
0
ß”¢*"·
4,
ä
•·•—
\x_
°'
Ü‘°
°'?‘‘
§
4
,_
VA
’4
'B
1•
1_
QQ
_4
g
V
"‘•.Ü'
N
3rf
GI
S
>·z
°°',‘
SF:
S<·-
SQ-
2;E
·‘
ab
ul{
gg
Ö
P"
_
gg
,
°1
0¤
E‘
¤°
...4Q
4Q
2**-
Q5
¤__‘„>
15
¤ä
11
.1'
{Äl
LO
SS
.·6
4„
-·—*¤.
E··
—
:Ü
Ö"¤.¤
d
Ö‘§
S
7
E
Ü
bg
gü
,
H0
0
·=
ka„¤
1
hw
5ä¤
|•
¢
”
·
§5
111ZI
•-•g
4z
‘w
SE
49
I
•·€
2E
E
_,S
zu•-
an
c3
U
w0
zIL
¤n
ää
2E
2
:,'an
‘.
u1
E
"8
„~'\Z
co
E
‘_;··
u..•
;'
2
\.
3
a:
E
8U
I*X
.,
8
o~
·¤
4*
iv4..
8
•£4
‘
Rg;
.»
„
G
Ul
~
"I
44
r
·c
‘!In
a:
¤*
on1
‘
gg
1-
1-
>-Z
o-s ‘
II
2ä
'~···ä
2
sä
NU"
P4"
·;'
QE
:I
¥·
5-g
g‘
4*·
·‘€¤-
•'·*·'
4° )9**
S°
°°‘U
-.
g°
E•
.l’*
,;I2
Qa
x
·z
¤__.__
~a·
4I
ag
U
M-!•—
#•·.
_
_|
q-
‘°‘
¤-
¢‘T
4<
_
E0
,_„.>
4*ÜQ
_
-¤
.;
'_
·'
”V
OG8
.
·
N"
'
JZQ
Ä
4b
i„
r
Q
ÄI
3
qi
un
5SIi"
":1ca
u4QS
I-¢
4*
u-°"
3II
.1us
>:
anE
lg8
ZI
•-•E
"E
ang
m
50
EE
WIA2
2¤
2S
äfE
EE
Y?S
’_,
E3
7<
>§
2Ҥ
•-ää
.gg
•-°°
E<
E%
<C
Q?
Em
ag
euIE
-21ä'9'M
OS
_.—
0
aEE
Yh
l/
•-o
o/
ä2%
z¤22EE“‘;
22
22
2E32
—EE?
SNO
|.l.VOO
'|:|O
.|.N3O
H3d
51
7
2
$2
5L12
S
=;•z
3
·gS_
5
EZ5
_ll-:Ih
ä!"'
5·35°·‘8
2'2
E2
E
P0
E
ä'E
Ea
°°IE
E2 ät
252
Q
‘ä°·¤
2
;5*6
2S
22%
.
S
äé
2
ge!
SN
C.
2
ag
NE
OU
EC
52
W AIgJW
‘䤤
r
E5
II
E§?.a
..
5°g
E
:v—
_Ü
r-
ig?
2§§
tlg
s;'—
gas
•-<
gg
g”
Eéäi
6
gg
N
an
Igg;
a
ääl
.•
Uzv
,
<
EB
S
"
E
aßä
ég
g
1
__
2._
Na
·
Eä
Gag
5*2*
6
äga"u.
5:
VÜ
IIIIIÄ
ä2
;.
"E
6IIIIIIIII
.Ia
m
*
_
662
rD-
**0
/3*aggain;§gä
2Z
222
""8
2IIIIIIII
=2=~·
'JE
62—
VEag
i8
+
3%§-E
9*6%
|||||||l||||""
zn
ä•‘SE32
22
22
22
’SNO
|.LvO0‘I
A01.N3O
H3d
54
CHAPTER 2
Time and Energy Budgets
ABSTRACT: Scan sampling techniques were used to quantify behaviors of American black
ducks (Anas rubripes) wintering at Chincoteague National Wildlife Refuge, Virginia, during the
winters of 1985-86 and 1986-87. Diurnal time budgets were constructed by distributing scans
over a time-tide matrix within refuge pool, saltmarsh, and tidal water habitats. Black ducksl
fed least and rested most when in refuge pools during the day. Black ducks fed most and
rested least when in tidal waters during the day. Black ducks curtailed feeding and increased
time spent in alert and locomotion behaviors in response to disturbance. Time budgets were
converted to energy budgets. Diurnal energy expenditure (DEE) was derived by weighting
expenditure within habitat by the proponion of time spent in all three habitats. Comparison
with literature values suggested that black ducks wintering in Maine and Virginia have similar
DEE at a given temperature.
Time and Energy Budgets 56
Introduction
Declining populations of American black ducks (Anas rubripes) over the past three decades
(Steiner 1984) have prompted behavioral research of black ducks on their wintering grounds.
Albright et al. (1983) invesiigated the behavioral responses of wintering black ducks in Maine
to temperature, wind chill, and the availability of ice—free foraging habitat. Black ducks rested
more and fed less with decreasing temperature and increasing ice, even as total daily energy
expenditure increased due to the demands of thermoregulation. These authors suggested
that black ducks in northern wintering areas experience times of extreme food shortage and
that there was evidence of a physiological set-point below which it is more advantageous to
rely on energy reserves than to expend energy searching for food.
Hickey and Titman (1983) employed scan sampling to study black ducks wintering on Prince
Edward Island. Similar to the tindings of Albright et al. (1983), ducks fed less and rested more
with increased wind chill and tide level. These authors suggested that there is a need to de-
termine the amount of time black ducks spend in various habitats and to measure nocturnal
activity.
Brodsky and Weatherhead (1985a, 1985b) demonstrated that local food availability can deter-
mine black duck behavioral responses to low temperatures in Canada. Brodsky and
Weatherhead (1984) also studied the posturing of black ducks while resting and roosting as a
mechanism for reducing thermoregulatory costs. That study suggested that the management
of energy expenditure is as much a consideration as management of energy intake by black
ducks.
In this study, the time budget approach was used to quantify behavior and energy expenditure
of black ducks wintering on, and in the vicinity of, the Chincoteague National Wildlife Refuge,
Virginia. Objectives were to estimate time and energy expenditure within different habitats,
Time and Energy Budgets 57
identify environmental factors that influence behavioral response, and contrast black duck al-
location of time and energy resources in tidal Virginia with results of studies conducted at
higher Iatitudes.
Study area
The study area was located on Virginia's Eastern Shore of the Delmarva peninsula. lt was
bounded on the east by the Assateague National Seashore (Maryland-Virginia border to the
southern tip of Assateague Island) and on the west by County Highway 679, from Swan Gut
Creek to the Wallops island bridge. This area included all of the Chincoteague National
Wildlife Refuge (3600 ha), the south end of the Assateague National Seashore, the north end
of Wallops Island, the south end of Chincoteague Bay, and encompassed about 25,600
hectares. At least 3000 black ducks wintered on the study area.
The study area was composed of 25% upland, 21% open tidal (21m deep at mean low tide)
water, 21% subtidal (<1m deep at mean low tide) water, 18% saltmarsh, 5% tidal flat, 4%
brackish impoundment, 2% natural pool, 1% shrub wetland, 1% freshwater stream, and < 1%
other habitats. Telemetry and aerial survey data from the winter of 1985-86 indicated that use
of the saltmarsh and refuge impoundments by black ducks was significantly more than pro-
portional availability (Chapter 1). Tidal waters (i.e., subtidal water and tidal flats) were im-
portant during periods of freezing temperatures, when other habitats were not available for
foraging.
Time end Energy Budgets 58
Methods
Scan sampling techniques (Altmann 1974) were used to quantify behaviors of black duck flocks
wintering on the Chincoteague study area. During the 1985-86 winter, 138 flocks were ob-
served between 5 November and 27 February. During 1986-87, 41 flocks were observed be-
tween 10 November and 1 February. An efforl was made to distribute weekly observations
over habitat and time of day. Flock size ranged from 10-880; mean and median flock size was
70 and 43 birds, respectively. The term "flocks" is used Ioosely in this context; observed
'fIocks' were not necessarily discrete biological units. ln most cases, a group of easily visible
ducks (within a flock) was selected for observation. During active periods, ilock composition
often varied among scans as birds moved in and out of the observation 'window".
The sampling procedure began with the duck farthest to the left or right (side was randomly
chosen), and proceeded to the next individual until the entire group had been scanned. Sub-
sequent scans within a flock started on the same side that was initially chosen. Regardless
of flock size, a minimum of one full minute was allowed to Iapse between the end of one scan
and the beginning of the next to minimize dependence of scan data. A flock generally was
observed for an hour or until 20 scans were obtained (whichever came lirst). This procedure
was followed to minimize llock bias in the time budget estimate.
Each duck was observed through a 15 - 60x scope for tive seconds or less, and behaviors were
categorized as feed, rest, stand, walk, swim, fly, comfort, alert, courtship, or agonistic (Albright
et al. 1983). Feeding included dabbling, tipping-up, and foraging behaviors often observed in
Held-feedlng ducks (i.e., walking with head down). Resting included sleeping and loating.
Comfort behaviors included preening, wing tlapping, stretching, and scratching. Courtship
included all pre- and post-copulatory behaviors. Agonistic behaviors included both intraspe-
Time and Energy Budgets 59
citic and interspecific encounters. A 10-key mechanical laboratory counter was used in the
field to tally behaviors.
Date, time, wind speed and direction, temperature, cloud cover, precipitation, ice cover,
habitat type, and location were recorded for each scan. Cloud cover was recorded in 10%
increments. Precipitation was recorded as absent or present. Ice cover was categorized as
none, light/intermittent, or heavy (i.e., thick enough to support ducks). Habitats were cate-
gorized as saltmarsh, refuge pool, or tidal water. Tidal water included tidal tlats, streams, and
subtidal open water. Refuge pool included both artiticial impoundments and natural pools.
When fiocks were disturbed by a recognizable source, the source was categorized as natural
(e.g., racoon or raptor) or man-made (e.g., pedestrian or automobile). Scan sampling contin-
ued while the disturbance was present (or until the flock flew away) to obtain a random sam-
ple of the behavioral response of black duck flocks to disturbance. Nocturnal observations
of black duck flocks were obtained with the aid of a Smith and Wesson night-vision scope, lit-
ted with a 400 mm lens. lt was difficult to distinguish black ducks from other dabblers; ob-
servations could only be made on nights with a full moon and some ice or snow to enhance
light reflection.
Analysis
Tidal stage was categorized as ebb, flood, high, or low. Low and high tides were exactly three
hours, centered on the corrected (for Chincoteague Channel) low and high tide times pub-
lished by the National Oceanic and Atmospheric Administration (1985, 1986, 1987) for Sandy
Hook, New Jersey. Ebb and flood stages made up the remaining time, each approximating
three hours. Tide height varied 0.6m between high and low water. The time of scan was
converted to minutes from sunrise and minutes before sunset for correlation analysis (NOAA,
Time and Energy Budgets 60
38°N). For analysis of variance (ANOVA), time was categorized as <3Vz hours after sunrise,
<3% hours before sunset, and midday (i.e., the time in the remaining interval).
Spearman rank correlation procedures were used to assess behavioral responses to weather.
The overall effect of habitat, time, and tide on black duck behavioral response was assessed
with multivariate analysis of variance (MANOVA), in which all behaviors were modeled as
mutually-inclusive dependent variables. Three-way ANOVA procedures were used to assess
the inliuence of habitat, time, and tide on energy expenditure and each behavior. Proportions
were arcsine-square root transformed for both MANOVA and ANOVA procedures (Zar 1984).
Time budgets were calculated from least squares means of behavioral proportions. Energy
budgets were estimated from energy coeflicients used by Albright et al. (1983). Signiücance
for all statistical inferences was pS0.05, unless otherwise indicated.
Results
Independence
The independence of scans within llocks was investigated. Plots of behavioral proportions
and energy expenditures against time of day suggested that some behaviors were related to
time. Therefore, proportion feeding and energy expenditure (for each scan) were regressed
against time to remove serial correlation due to time, and the residuals of the model were
analyzed for statistical autocorrelation using an autoregressive integrated moving-average
model (PROC ARIMA, SAS-ETS 1984). The proportion feeding was selected for analysis be-
cause it was the most dynamic behavior.
Time and Energy Budgets 61
Only 12 flocks had >25 scans, the minimum number of observations recommended for esti-
mation of autocorrelation by PROC ARIMA. For energy expenditure, only 1 of the 12 flocks
showed significant first·order autocorrelation between scans. For proportion feeding, three
of the 12 flocks showed signiticant first-order autocorrelation and one showed significant
second-order autocorrelation. This procedure suggested that a lag of tive minutes between
scans sufficiently reduced problems of statistical dependence. Consequently, scans less than
five minutes apart were discarded from the data set; 1471 diurnal scans from 179 flocks and
47 nocturnal scans from 7 flocks were used in the following analyses.
Influence cf weather
The influences of cloud cover, wind, and temperature on behavior and energy expenditure
were assessed with Spearman rank correlation coefficients (Table 13). Swim, comfort, and
courtship behaviors were positively correlated with cloud cover; rest was negatively corre-
lated. Feeding was positively correlated with wind speed; stand, walk, comfort, courtship,
alert, and agonistic behaviors were negatively correlated. Rest, stand, and comfort behaviors
were positively correlated with temperature; feeding, swimming, flying, and energy expendi-
ture were negatively correlated with temperature. All correlations, except for that of energy
expenditure with temperature, were low (r<0.25).
influence of habitat, time and tide
Habitat, time, tide, and their interactions influenced the behavior of black ducks wintering at
Chincoteague (MANOVA, p=0.0001). However, individual behaviors within the MANOVA ma-
trix did not always respond in a similar manner (Table 14). For example, feed, rest, stand,
swim, maintenance, and alert behaviors were dependent on habitat whereas walking, flying,
courtship, and agonism were not.
Time and Energy Budgets 62
lnterpretation of behavioral responses to tide is confounded by habitat use considerations.
A positive relationship between low tide and foraging behavior has been found in tidal habitats
in maritime Canada (Hickey and Titman 1983) and coastal Maine (Hartman 1963, Albright et
al. 1981, Jorde 1986). In Massachusetts saltmarshes, however, Grandy (1972) found evidence
of a positive relationship between high tide and foraging behavior. Consequently, the effect
of tide stage on black duck behavior must be investigated by habitat type.
Black ducks clearly changed their diurnal feeding frequency in response to habitat and tide,
and less so to time of day. When in the saltmarsh (Figure 9), black ducks spent the most time
foraging during high and low tides. ln tidal waters (Figure 10), black ducks spent significantly
less time feeding at high tide; however, during other tide stages black ducks spent signif-
icantly more time feeding in tldal waters than in either refuge pools (Figure 11) or saltmarsh.
As expected, tide stage did not significantly affect foraging behavior in refuge pools (water
levels are not tidal).
Time budget estimation
MANOVA and ANOVA procedures suggested that time, tide, and habitat are important factors
to consider when constructing a time budget for black ducks wintering on the Chincoteague
study area. Albright et al. (1983) were able to equitably distribute observations of black ducks
on Maine tidal flats by sampling at fixed times during the day. However, at Chincoteague,
black ducks have several available habitats and move among the habitats (Chapter 1) to
accomodate foraging strategies; behaviors must be sampled as liocks are encountered.
Consequently, scan data were distributed ex post facto over time and tide, by habitat. Two-
way tables for time°tide (3x4) interactions, by habitat, were calculated for each behavior.
Least square estimators were used to calculate the overall mean and standard error for each
behavioral proportion. This procedure accounted for the unbalanced cell sample sizes and
the covariances among cells when calculating the standard error associated with the mean.
Time and Energy Budgets 63
The least squares estimates of mean and standard error for each behavior were used to
construct a diurnal time budget within each of the three habitats (Table 15).
Black ducks fed least and rested most when in refuge pools; conversely, they fed most and
rested least when in tidal waters. Black ducks were particularly active in tidal waters, ap-
parently curtailing rest to feed and swim more. Black ducks used tidal waters primarily when
ice limited the availability of saltmarsh and pool habitats (Chapter 1); their behavioral re-
sponse in this habitat was likely due to lower temperatures rather than some habitat charac-
teristic.
The time spent in flight was underestimated by scan sampling. Flights between roosting and
foraging sites were not accounted for because ducks quickly moved out of view. Telemetry
data, however, suggested that black ducks on the study area generally flew 2.8km between
foraging and roosting sites (Chapter 1); a conservative estimate of time required to fly this
distance, allowing time for milling, would be 10 minutes.
Energy budget estimation
Time budgets can be converted to energy budgets by weighting each behavioral category by
an appropriate multiple of basal metabolic rate (BMR). Additionally, the cost of
thermoregulation at 5 - 10°C, 0 - 4°C, and -10 - 0°C can be factored in as, respectively, 1.4, 2.0,
and 3.4 times the BMR. Temperatures 210°C were assumed to be in the thermoneutral zone
(Wooley 1976). Basal metabolic rate was assumed to be 3.204 kcal/bird/hr. All BMR multiples
used in this analysis were obtained from Albright et al. (1983).
The energy expenditure (kcal/bird/hour) of black ducks at 5°C was calculated for each habitat
(Table 16). Hourly energy expenditure=[(muItipIe)(BMR) + cost of thermoregulationl x pro-
portion of time spent in a given behavior. Total hourly energy expenditure was the summed
Time and Energy Budgets 64
energy cost of all behaviors within a habitat. Total hourly energy expenditure was then
weighted by the proportion of time that black ducks spent in each habitat (Table 17). This
weighted value (6.80 Kcal) represented the hourly rate of energy expenditure at 5°C by an
average black duck wintering on the Chincoteague area during the day.
This same approach was used to estimate energy expenditure for each scan and its corre-
sponding temperature. Not surprisingly, estimates of energy expenditure for scans were sig-
niticantly correlated with temperature (Table 13). Scan energy expenditures also were
correlated with time; as the day progressed, energy expenditure decreased.
Estimates of diurnal energy expenditure also may be extrapolated to 24 hours. Nocturnal
feeding has been reported in dabbling ducks in the summer (Swanson and Sargeant 1972) and
in the winter (Mendall 1949, Tamasier 1976, Albright et al. 1983, Jorde et al. 1984). Although
nocturnal data collected during this study were not adequate for the least squares means
procedure, the arithmetic means (Table 18) suggested that black ducks were indeed foraging
and swimming actively at night. Twenty·two of 62 carcasses collected on the study area dur-
ing the day had empty digestive tracts and aggregate dry weight of ingested food in the other
carcasses suggested that black ducks were not actively feeding during the day (Chapter 3).
Circumstantial evidence from radio telemetry (Chapter 1) also strongly indicated that black
ducks were active outside the Chincoteague NWR at night.
Day-night habitat use patterns of black ducks on the Chincoteague study area were very dif-
ferent (Table 17). lf nocturnal and diurnal behaviors within habitat are assumed to be similar,
as these data suggested (Tables 15, 18), the energy budget can be extrapolated over a 24hr
period by weighting the estimate of energy expenditure by proportional use of habitats at
night. At night, black ducks spent 5.2hrs foraging and expended 7.07 kcal/bird/hr at 5°C.
Tlme and Energy Budgets 65
Disturbance
Of the 179 flocks sampled during this study, 38 were disturbed at least once during the ob-
servation period (approx. 1hr). Of the 38 disturbances, 66% (25) were of human-origin and
24% (13) were natural. Human disturbances included pedestrians (5), automobiles (10), boats
(2), hunters and oystermen (4), and aircraft (4). Natural disturbances included flocks of snow
U.S. Fish and Wildlife Service, Newton Corner, Massachusetts. 300pp.
Swanson, G.A. and A.B. Sargeant. 1972. Observation of nighttime feeding behavior ol ducks.
J. Wildl. Manage. 36(3):959-961.
Tamasier, A. 1976. Diurnal activities of green-winged teal and pintail wintering in Louisiana.
Wildfowl 27:19-32.
Weathers, W.W., W.A. Buttemer, A.M. Hayworth, and K.A. Nagy. 1984. An evaluation of
time-budget estimates of daily energy expenditure in birds. Auk 101:459-472.
Wooley, J.B., Jr. 1976. Energy expenditure of the black duck under controlled and free-living
conditions. MS thesis, U. of Maine, Orono, ME. 106pp.
Time and Energy Budgets 74
6·¤E*6>.
EU!
=
6
5-C
gLU
ä
¤
8
E
=
2
‘”
2
2
‘°
Eca<
E
E
·~
E
gg
Q
3
2-c
EÜ7
U
•·2
S
‘
x:
t
'
¤
2
ca
83
<
8
¢-
Va
:
vr
°
au
-
°·8
B
o
Y
E
o
Nt
O
‘8
1**
••-
Zg
tb
F
.
°
lg
O
g
••g
g¤·
‘__
D
2
·2
E
uni
>_
N
„,
:
ää
E
°2
·
Q'E
°
°°
6:
'
26
E
2
—92
EZ
§
.
°
cu
"‘
';
co
°
·
=
.,.
Ei
‘“¤
E
5;
o
8
m
"'¤•
—
cn
•-
:
$.2
£
Q
ao
t~
v;
cu
.ö>
.-
rg
··:
g
3
$2*
„
·‘2
S
r:
GG
‘¤
g
Q
E
,*1
Sg
ä
Q
•
ln
·
{
•C
c
äo
6
2
$3
"
"
o
°
c
·
o
·¤
gs
··
·‘2
§
.1:
{B
N
·-
6
o
-
ea
cu
6·-
2
·2
==
Ä
·=·
"•T•'
cg
S
nv-
'”
é
".°é
r~
°°
U
E
;
g*
~¤
(D
V
0
Q
E
1-
N
S
3
¤..
**7
ca
°
o
¤¤
'
E
"*
„ä
·—
‘
·»
E8
2
E„
2
E2
N4!
r~
°·<r
M
E
¢*
85
°'3
‘*
·
„.
N
Mg
·
2
0
:
1:
·
>
¤
‘
,5:
"
o
E
„-o
·‘2*
¤
¤-
an
•¤
S
,%*6
·
=
T6
¤>
.
2
*77
P?8
··
EE
E
Z
¤.
8
„g
=
E
26
T6
‘°
v'
>
n.
'U
Q
E
A-
88
,_-3
__
3
‘;
26
22
28
2
2
I-
•¤O
ua
¢
an
cu
g
U
D
.¤
ö
0*)
'D
g
:s
c:Q
E
E
g
‘°E
g
9
E8
Ö
"’
„_
0
°
2
I-
0
N
cd
:
6
‘
'··¤
¤>
s=°°
***8
°ö
6
2,
2
:3
*°·"
o6"’
¤
ug
«»
EZ
m
¤><¤2
!'>-· ä9
76
232
2
SE
ä
2.
*6
<
§¢
¤
S12
dä
I
3
V"
S
Q
-§
3
U
E
ÖG
°6
5:
¢‘§
..
1:
3
·
N
•2
5;
eg
<
Ih
Ü
gg
<
'd6
dg
>
2
ß.
N
«-v-
2
§6
‘ö—
-dä
‘8;
6
u
3
ci
6_
„
E
'-
G
Q
G1
-
Ög
df}E
5
·ä.,d
§
°’§d
ä
‘
§„d
¤
·§..d
ä
-3
i
°'.
gq
eg
ß
q.8
6>
Ia
ä
1%
·6
..d§
·2
„d
¤
°’§
8
6·~
3
dd
“"”"
Q
ep
„
F
.8
Ö
E
°**
"§
gä
ää
°§
dg
°
2
a
2
«¤
6”
•¤
2.-
s
g
2
·2..d
"~‘F
·;..d
§
-3
2
-
3
dä
dä
dg
3
2
¤.-
:
Su
lg
w
$„,°8
«¤
S.
gg
g
.w
dg
.3
dä
9
2
W
V
°""
r~=
·>
"
m
¤.
-6...
-—
dd
6
63
6
6
ss
38
ö’d
°“°
*‘
=·=
'dä
2
-*6J;
¤•
6
ä
6<~·
dd
Q
:;“
2dg
ä'ä
§
ä·=
·”§
·=¤
.g•¤
;§··
Bw
'
3
„-'8
--
2:
ae
6
§
.3
6,,
.3
dä·
E2
35
-·§
dä
"'3
dä
Ԥ
2
~,=
Ev
12
.;
.=
Q.,
¢D
1-
*,9
E"
6
.«
6•¤
‘°ä
6
216
äv
un
"°"
*8
r~
·°
§
äz
.6
·2
-d
§.,·
2.,,d
-ä
6g
E5
dg
.;¤6
g,
C;
-¤.¤
=‘
==
Q
Oc
6.
··
-¤
~
6
*°=¤ci
°
••"'
cw
d
-v
6N
do
8
an
nn
,.
v~
6.,,
l|
gz
ga
.2
dg
dt!
6
2.-2
og
”"’
a
¢•·
0**
,..
E
g
ég
.w
d
B:
e:
*6
In
S
E
*3
5;
s-
Q
·
cE
¤-_¤
u
cu
«-Sg
5
gu
ga
ää
-2
ä
§
·ä
.„d
§,
2ä
E:
*2
21T
2
‘"
dä
·2
Ԥԡ6
Ep,
-¤-ng
;
"‘··
Eä
ä
ag
**3
;;
d§
03
2
-5
Bs:
||-·•--3
;
JL
r—
Ö
g<
gn
ug
g-E
d
.-In
E
N
mzä
z
.26
3
*;*22
.
3
g<
3<
2d.=,—
·l22
2-::
*6.6-E
gw
we
gg
-
·<
gS
!;"
·¤
$Q
°**~
«2
-E
•=
1?
,·5;6
22
;
Eiä
äg
lj
.·=‘¤
>'°‘•=
·—
3ä
E=
2
Ü
U.!
•'¤
<°°¤
**u
.n
¤>
·¤o
<¤
¤
Id.:-—
22
d2=
2
igä
eva
22,622
we
e;
éegeg
-IZ
<"
22
22
IÜS
E
äg
äg
ä
"’
ä=
·¤.S
'j
22
22
;
2:,2
;.dg
F22
E3
nl- B
.
V
76
uf
C•••°_
c
gä
§ä
„-§
><
'•
Q-
5
'·
88
Eo
5
,,,-
¤1:
c
N=
•-
s6
ä2
Q—
EQQ
2‘
·S
Q§§
Ei
E
°‘
aa
G-
"¤
bl
<8
3„-
Q
2·
·Q
8§
§E
E
'·
Y
6Ü
Q
.E_
2
„,
sE
8Q
•.3
2
Q3
Q8
2g
F3·~
¤
g
°·
QE
Q2
-¤h
oz~
•··
2Q
S2
äg
·~„
Q
g¤
o
Q-8
J·E
'”¤=
§Ä
2ä
E$2
„-,.
$$2
n°
Q"Z
GQ
NE
"
4:
‘·
Q0*5
Ex
E"'
„Q
Ss
Eg
Qw
s
2·
·~
Qä
EE
=
um
2E
gs
Ö
E‘“
§¤~
2Q
Q.
8Q
ä-
25
E
”‘
.U
m
E
3**
:17;
S';
gä
so
o
·Q
ng
„-$2
goU
gn,
Ea:
*5Q‘=
SS
Ev-
Q,5
c
bm
¤.2
za·-
22Q
.8Q
Üä
·°*Q
S3
gH
g
•¤'°'
‘$°3
Q3
SC
cm
uu-·-
o=
Sg
:IY
*·_O
m‘”
—¤·E‘
0Y
—·¤
mu
¤.O
1:·
U_C
,.,2Q
¤.0
::0
UI-¤
¤'ll.!
EQ.
NN
"
V)'·‘·'
Eaa
Qi!
Gm
ggth
_|l}-
am
¢\.
-2
äs
Ihn
-
"Eul
$.35
22Q
2=
93
ac
|·l-O
l"U
)-|I-Z
LuO
—|
(Z<
Ec
°‘°-
Ü:§
¤<
3F
77
Q¤S0
EE
E-96
§·-
.6
,,,*-2.2,;
caN
.6
5N
SS
lgM
?23
¤¤"
Ö6
-8
é'2
gi3
3
338%
..
N.
Qc_
_
%E
"N
·§„.;fg
::
6g
g!
~N
gg
gq
Ü
N@
Q-
g
,,,2
·6
8E
N-2
;%ӊ
0
IN
Q"
.·=
E
tg
G
NE
.:g
d
QW
Q-
Q
•-•}
.
za;-
cmQ
S
s.
88
Q°'
N
00
-·
9
'Ö
8Q
§8
sx
Oc;
°Ö
C1
-
UE
-Ö
02
_9¤‘>
8Ö
U)
•-•O
L
6·
<=S6
S..,
38
56
Y-°
'Ö
§Q
‘°9
0
Q,9
.Ö
cf
QE
EE
'-Ö
ai
QN
N
EX
.:"
6-
ÖQ
RQ
¤_g
5·
·6
w'Nv
66=¤
E
In
8 56<—·
N.'
°2
Q:
E9
Ö
‘·‘·~·8
N-eo
Ö
GJ><
:9.
‘Ö
8cu
N
"’
•'*;;
¤„g
.ca
0Ö
Sr-·
¢¤
*'—
a
_§2
‘Q
8g
Nsf;
6;
(AN
FQ
gn‘_
=
:J‘_
•-•,_
C
•gn
gp
-G
ig
'1-
,.va
1-
O5
.;:g
w-
2.6
.·
Nm
.¤,_
\n
g
F
N
1
=S=‘-.:.2
N,
°’S
882
25
>~;?·‘
83
s.·NN
E6”‘
28
E:
‘Ö
ÖQ
hlÖ
EE
V.1:;:
°“
-6
‘Ö
3Q
0N
.-"·'·¤
gw6
·6
=¤<>u
Q:
ÜN
Q]
(D
¤¤•,,
NN
—°’
••°
u-
mo
"'-
•-8
QN
1-
gg
¤L
n
ug
‘Ö
Ö
oS
mB
0)
32
•-·'
Öä
Ög
+'ö
"3‘
N-vr
.·
,9E
EII
'V
"
3M
Q-
g'
~N-
vew
g5
66"*
.8
_¤.
F:
¤E
I0
;
NE
Uv-
NÖ
¤-
•'
0¤
.•-•··
Ö"
_N
'¤
***2
NÖ
cneo
0—
Ecc;
0
.Ö
hl
Ö0
¤„_
5:1
Ä
“°’Q
“E
0¤."ö
B"
2
'"°
°';:,.:
xn.
8*3§
_ä
.82
2*6$2
S6
2·¤
8
¤‘
gé
vz.
¤>°
:¤.
U"Q
u.:O
_;·¤
0"?
:-9
¤•
Iu.:
°·
5:0
5*
°·‘.::
N
QE
LUÜ
Q—
•-•
uß
Izu
·¤ca
0
6
6.‘°
:
0
:"‘
°',-2
zää
„,
°·’·;8.‘3
lg:
NN
:
D_
'
8•.\0
N
Po
U-
I
5‘¤
__
,•-·0
Wo
50
_,M
26
::6.93
ex°
<°‘
<m
*6W
Q.?
·¤<¤
°-<
•->
„—-
0*-
U}E
Q
Q-¢
¤.g
..„
N-
(ä
ng
.,n
g
*"E
6g
x<
6w
u.1I
"*5
2,
•·.
78
Table 17. Pr¤portionaI’ day and night use of three habltats byblack ducks wlntering at Chlncoteague, Virginia, -15 December 1985 - 28 February 1986. ~
HABITAT DAY (n = 753) NIGHT (n =689)
Refuge pool .519 .110
Saltmarsh .396 .595l
Tidal water .085 .295
’Based on 1442 radio locations for 21 female black ducks.
79
Table 18. Noctumal tlme budgets for black ducks win-tering at Chincoteague, Virginia, November-March 1985and 1986.
Feed .442 _ .052
Rest .267 .048
Stand .002 .002
Walk .023 .009’
Swim .236 .040
Fly .002 .002‘
Comfort .022 .006
Alert .005 .003
Courtship .000 .000
Agonistic .000 .000
‘Arithmetic means based on 47 scans from 5 ilocks intidal water, 1 tlock in saltmarsh, and 1 tlock in ref-uge poolhabitats.so
0.9
B:
Q.
_
I·
E
-O
§§
§N
cn
2Q
--
.8
6.2
<’
„
E°
·
S¤
ä..
äé
‘°*'
1-2
S0
.3
88
E2
sa2
8
,._
G}-=
"3
S*1
8*5
82.
61:
‘¤
0O
-·
Q•—
cl
N
2E
68
22
2{
8·
-.
.2
2'U
2:
E_z~
3$
··¤¤
‘°
E¤·
·<Q
'EB
2.
·äE
CE
g
1:.-
·g
sE
E3E5
v8
cn1*
c.
--
28
2N
C
88
Qx
anJ;
EQ
§C>
r~E
•··E
Q.2
'•-
S*8
"8
.6C,
E
§6
QQ
8_
¤
"E
¤•·E2
OE
Qln
C)
Q...
E¤<
*<8
83
28
88
vi•
'D•
0gg2
g2
22
8C
Pu
‘·
QN
O2
g_·¤°
E
··ä8
EC
gL';
IhQ
·—.
··¤¤·—
.9=
EQ
!C
tzCh
o"
oO
5
‘äQ
¤·W
EU)
*6
Q?
:
•.d
l
dg
-¤‘°
•'Ez
<-=
.
gg
,<
,,¤¤
.9:
ggE
<¤E
2SS
·_zD
II<
IIG
"I
gZ
.
81
Table 20. Dlstrlbutlon‘ of lntraspeclllc and lnterspeciflc agonlstlc encounterswlth black duck: wlnterlng In three habltats at Chlncoteague, Vlrglnla,November-March 1985 and 1986.
SPECIES REFUGE POOL TIDAL WAT€R SALTMARSH
Black duck 114 9 13
Mallard 11 1 0
Canada goose 1 0 0
Gadwall 1 0 0
Hooded merganser 0 0 1
man _ E iö TZ
‘Based on 80,988, 6,710, and 14,135 observations of black ducks in refuge pool,tidal water, and saltmarsh habitats, respectlvely.
82
Table 21. Comparlson of dlumal tlme budgets (lnhours) for black ducks wlnterlng In Maine and Virglnla.
Feed 4.54’ 4.49
Rest 3.80 ' 4.54
Stand 1.07 0.08
Walk 0.03 0.13
_ Swim 2.66 1.83
Fly 0.01 0.07
Comfort 0.27 1.07
Alert 0.01 0.15l
Courtship 0.00 0.02
Agonlstlc 0.00 0.02
Total‘Data
from Albright et al. (1983) at 5°C.
'Behavioral data from Table 14; behaviors areweighted by dlurnal habitat use data from Table 17.
'Proportlons converted to hours spent ln each behav-lor out of a 12.4hr day.
83
II
•
Ij
I3
¤
:
3 §:
IL=
III
;5
J1
..
//
:§
.
-¤
„•°°
°
\
äuv:
f:
*1:
:
.
Q
°‘•··
/
¤
gs
/
_•'
-
IL-g
g
//
’G
gg
.=
S
1
·
‘é'ES
·‘
\
I:··E
-·
5..
•
ßa
\
•-G
2
;
äa
S
z
„é‘
2_
2;
SN
IQB
6QV
fg
3:}NO
6E
gg
Ua
°
:5
O
¤·-
dOg
EF
dN
••
Vgw
84
IEE
„,.2
I!I
.2
*2E
II
EI
\"
E
u.$
‘°
I\
Eß
O
2.
g22
\s
—§§
:"G
\ää
‘22
uaE
5
·E
3°
33
33
33
33
E)N
ICI33:I
NO
|.I.I:IOdO
Hd
NVBW
I
85
2E2‘
G.¢
II
Eun
S
1iI
12
22
2\
21
32°
>-"ö
„
I.
E==
2%„
\‘
_/=
Eäg8
6
\E
äg
\;.2%
AE?SI2;
/5
\Q
ga°
<Ü
%2E2I
22
2.2
AE)NIG33:I
NO|.LHOdOHdnvaw
86
CHAPTER 3
Carcass Composition
ABSTRACT: Sixty-four American black ducks (Anas rubripes) were collected during early,
mid, and late winter at Chincoteague, Virginia, in 1985-86. Whole carcass analysis indicated
that black ducks were at least as fat and heavy in the spring as they were in the fall. Com-
parisons with similar work in Maine suggested that black ducks experience a negative energy
balance after mid·winter, the extent of which may be determined by the severity ofthe winter.
Regression models were derived from body weight and external measurements to predict
physiological condition of live black ducks (R’=0.63).
Carcass Composition 88
Introduction
American black duck (Anas rubripes) populations wintering along the Atlantic Flyway, as de-
termined by annual Mid-Winter Waterfowl lnventories, have declined almost 50% since 1954
(Steiner 1984). This represents an annual rate of decline of almost 2% for the past three
decades. The black duck, which has historically ranked first in the Atlantic Flyway harvest, is
now third behind the mallard (Anas platyrhynchos) and the wood duck (Aix sponsa; Blandin
1982).
Excessive harvest (Geis et al. 1971, Grandy 1983), habitat loss (Spencer 1981), changes in food
availability (Perry and Obrecht 1983), pesticides (Heath l969, Longcore and Samson 1976), acid
precipitation (Hansen 1987), and hybridization with mallards (Johnsgard and DiSilvestro 1976)
have all been implicated as factors contributing to this decline. Recently, attention has been
directed towards the dynamics of waterfowl populations on their wintering grounds (see, for
instance, the 1982 Workshop on the Ecology of Wintering Waterfowl and the 1984 Symposium
on Wintering Waterfowl). Fretwell (1972) argued that environmental factors outside the
breeding season were crucial in regulating populations of migratory waterfowl species, and
recent studies have indicated that the condition of waterfowl leaving the wintering grounds
strongly influences reproductive success during the subsequent spring (Ankney and Maclnnes
1978, Krapu 1981).
Physiological condition of homeotherms is considered to be a direct function of total body fat
relative to body size. Body fat represents efficiently stored energy. It has twice the caloric
density of protein (Ricklefs 1974) and only 0.2-0.3 grams of fat per gram of nonfat tissue is
needed to maintain functional homeostasis in birds (Odum et al. 1964). Fat levels in birds can
vary from as little as 2% of the body weight of starving cockerels to more than 40% of the
body weight in premigratory passerines (Griminger 1976). In black ducks, mean fat levels vary
Carcass Composition 89
from 4% to 16% of wet body weights of postlaying females and premigratory females, re-
spectively (Reinecke et al. 1982).
Fat levels in waterfowl are generally assessed by ether extraction of plucked, dried,
homogenized, whole carcasses. Results are expressed as percent fat or as grams of fat per
bird. Although whole carcass analysis has been conducted in several waterfowl species,
black duck carcass composition has been investigated only once, in Maine (Reinecke et al.
1982). Clearly, more studies of endogenous energy reserves in black ducks are needed. The
Workshop on the Ecology of Wintering Waterfowl (1982) specitically addressed Iatitudinal var-
iation in fat reserves and maintenance of fat reserves over winter as important research
needs.
Several researchers have investigated indices for assessing the physiological condition of
waterfowl in the tield. Total body weight is generally expressed in some allometric relation-
ship with external physical measurements (to account for individual differences in body size)
and correlated with either total body fat or a fat index. Alternatively, weights of various fat
depots (e.g., subcutaneous, omental, visceral) can be correlated to body fat. Harris (1970)
used keel and culmen Iengths when correcting for body size variation in blue—winged teal
(Anas discors). Owen and Cook (1977) used the body weight to wing length ratio as a condition
index for mallards. Woodall (1978) used omental fat as an indicator of condition in red—billed
teal. Bailey (1979) evaluated the relationships of body weight, skin weight, several fat depots,
and bill, culmen, keel, and total Iengths to total body fat in the redhead duck (Aythya
americana). Chappel and Titman (1983) used body weight, whole skin, plucked skin, various
fat depots, and body length as condition indices for the greater (Aythya aftinis) and lesser
scaups (Aythya marila). Various condition indices also were used by Whyte and Bolen (1984)
and Ringelman and Szymczak (1985) to assess total body fat in mallards.
Other researchers have used blood characteristics as indicators of physiological stress.
Harris (1970) found that plasma free fatty acids, glucose, and nonprotein nitrogen were related
Carcass Composition 90
to weight loss in incubating blue-winged teal. Korschgen (1977) showed that hematocrit per-
centages and levels of total plasma protein and free fatty acids were indicative of degenera-
tive changes in breeding common eiders (Somateria mollissima). Blood glucose, uric acid,
and urea in green-winged teal (Anas crecca) were found by Bennet and Bolen (1978) to be
correlated to certain weather variables in winter. However, blood characteristics were not
correlated with total body fat or body protein.
In waterfowl, labile protein in the gizzard and flight muscles may constitute a source of
endogenous energy. Gizzards lose weight in waterfowl during nesting (Keith 1981, Korschgen
1977, Reinecke et al. 1982), and flight muscles lose weight during wing molt (Korschgen 1977,
Ankney 1979, Bailey 1985, Raveling 1979, Reinecke et al. 1982) and during the winter.
Korschgen (1977) attributed these weight Iosses to active protein mobilization but Ankney
(1977) believed atrophy due to disuse to be responsible. Work by Jones and Ward (1978) on
the red-billed quelea (Quelea quelea) and by Bailey (1985) on redhead ducks indicated that
at least some of the gizzard and pectoral muscle weight Iosses are due to active mobilization
of endogenous protein.
The purpose of this study was to investigate the body composition of black ducks wintering in
tidal Virginia. Objectives were to estimate changes in body fat and protein over the winter,
and to compare body composition of black ducks wintering in Virginia with that of black ducks
wintering in Maine. Indices for assessing the physiological condition of black ducks also were
investigated; these were based on weight, external structural measurements, and blood
characteristics.
Carcass Composition 91
Study area
In addition to investigations of body composition, habitat use and behavior of wintering black
ducks were concurrently studied on 25,600 ha on Virginia’s Eastern Shore of the Delmarva
peninsula. At least 3000 black ducks wintered on the study area. This area included the
Chincoteague National Wildlife Refuge and was composed of 25% upland, 21% open tidal
(21m deep at mean low tide) water, 21% subtidal (< 1m deep at mean low tide) water, 18%
‘Carcasses (n =64) collected during three periods in winter 1985·86; 12 October~11 November
(early), 16~30 December(mid), and 31 January-13 February (late).
*P|us or minus one standard error.
117
Table 26. Pearson correlation coefficlents of extemal measurements (mm) with selectedcarcass components‘ from black ducks wlnterlng at Chincoteague, Vlrglnia, October1985·February 1986. -
‘lncludes length of bill (LBILL), culmen, tarsus, wing, and keel, and width of bill (WBILL)and head.
*Signilicantly different than zero (p <0.05).
"Signiticantly different than zero (p <0.01).
118
Table 27. Partlal correlation coefllclents ol body weight and structural components re·gressed on physlologlcal condition ol black duck carcasses‘ collected at Chincoteague,Virginia, October 1985-February 1986. _
WEIGHT LBILL WBILL CULMEN HEAD TARSUS WING KEEL
Lipld Index 0.548 0.029 0.053 0.007 0.007 0.049 0.013 0.100
‘Sample size=62; 2 measurements of head width missing.
l
119
Table 28. Selected models of weight, water, and welghtzstructure ratlos regressedagainst the Ilpld Index (g fatlg nonlat dry carcass) ol black duck carcasses collectedat Chlncoteague, Vlrglnla, October 1985-February 1986.
The following equation is used for sites (south of Cape Cod) with estuarine vegetaled
wetlands:
Habitat Suitability Index Model 128
HS|[vw] = ((2 x SI,) + SI, + Sl,) /4.
An overall HSI value can be calculated by weighting each of the previous values by the rela-
tive areas involved (A[ow] = proportion of site that is subtidal open water; A[vw] = proportion
of site that is vegetated wetlands; A[ow] + A[vw] = 1):
HSI = (A[ow] x HSl[ow]) + (A[vw] x HSI[vw]).
A partial application of this model to 23 study sites along the Atlantic coast from Virginia to
Maine indicated that physical habitat characteristics alone may account for 22-29% of the
variation in the distribution of wintering black ducks (Lewis et al. 1984). The biological vari-
ables for this model were not measured; consequently, the model has been neither verilied
nor validated. In this study, we applied the model to a 25,614 ha study area on the Eastern
Shore of Virginia’s Delmarva peninsula. The area included the Chincoteague National Wildlife
Refuge, part of the Assateague National Seashore, and adjacent tidal habitats. Objectives
were to evaluate field measurement of the model variables and the overall model output for
the winters of 1985-86 and 1986-87.
Methods
Cartographic data were measured with a Tektronix 4051 electronic planimeter. The area of
subtidal water (V,) was estimated from bathymetric contours on 1:24000 USGS topographic
maps. Areas of tidal flats (V,) and streams, ponds, and impoundments (V,) were determined
from 1:24000 National Wetland Inventory (NWI) maps.
Cover of rooted vascular plants (V,) was assessed from approximately 100 aerial photographs,
representing 27 different locations, taken on 10 December 1985 from 1100-1200' AGL. These
Habltat Sultabillty Index Model 129
locatlons also were photographed in December 1986 but print quality was too poor to be
considered reliable; consequently, V, was assumed to be the same for both years. Photo lo-
cations were nonrandomly distributed over the study area. Locations were selected that could
be identified easily on USGS topographic maps. A 50 mm lens and Kodak Ektachrome (200
ASA) film were used; however, the slides were developed as 8x10 high-contrast black & white
prints. Cover was estimated with a dot grid (64 dots/in’).
Clam densities (V,) were estimated from ten 100 m transects perpendicular to the water’s
edge on selected tidal fiats at low tide. Transect starting points were randomly chosen for
each flat. Each transect was divided into five 20 m sections and two 0.1m‘ sample plots were
randomly allocated to each section within 10 m of the transect line; therefore, 100 0.1m’ plots
were tabulated each year. Sand and silt, to a depth of4 inches, were sifted through by hand.
Clams were tallied by species. Transects were completed during 19-26 November in 1985 and
28 November-14 December in 1986.
To assess the frequency of Ruppia and Pofamcgeton (V,) in impoundments, we completed the
fall vegetation survey which was normally conducted by Chincoteague NWR personnel. Ref-
uge impoundments constituted only 4% of the study area but represented 70% ofthe available
fresh to brackish standing water. The refuge survey had been conducted annually during the
past decade, but was not scheduled during 1985 and 1986 due to lack of funds. Seven
transects, in seven impoundments (A, B, C, WFN, WFS, Old Fields, F) were completed. Addi-
tionally, three more transects were completed within these pools (WFN, WFS, Old Fields) to
improve distribution and size of the sampling effort in 1985. ln 1986, however, only one addi-
tional transect was completed (Old Fields). A five-point sampler was placed at 10 m intervals
along the transect and vegetation at each point was recorded. Totals of 714 stations (3,570
points) and 497 stations (2,485 points) were sampled in 1985 and 1986, respectively. Pool
totals were weighted by the relative area of the pool. Transects were completed during 23
October-15 November in 1985. and 13-22 November in 1986.
Habitat sultabllity Index Model 130
Snail densities (V,) were estimated from twenty-six 100m transects nonrandomly distributed
over the study area. The sampling design was similar to that used for estimating clam den-
sities. Each transect was perpendicular to the water’s edge, divided into five 20 m sections,
and two 0.1 m' sample plots were randomly allocated to each section within 10 m of the
transect line; therefore, 260 0.1 m' plots were tabulated each year. All snails on the ground
(within the frame) or on vegetation that was rooted within the frame were counted. Snail
species, plant species, and average height of Spartina alternifolia within the plot were re-
corded. Transects were completed during 22 October-28 November in 1985 and 14
November·11 December in 1986.
Results
The study area was composed of 6562 ha upland, 5518 ha deep subtidal water (>1 m), 5386
ha shailow subtidal water (S1 m), 4743 ha saltmarsh, 1400 ha tidal fiat, 910 ha impoundment,
423 ha natural pool, 324 ha shrub wetland, 304 ha stream, and 44 ha other habitat. Other
habitat included areas designated as dunes under the NWI classification and were pooled with
upland for this analysis. variables and corresponding Sl values are estimated for both years
in Table 34.
Shallow subtidal water (V,) covered 49.4% of the open water area at mean low tide; 11.4%
ofthe total open water was exposed at mean low tide (V,). Ponds, creeks, and impoundments
(V,) represented 24.4% of vegetated wetlands. These physical variables were assumed to be
the same during both winters.
Approximately 17.4% of shailow subtidal water supported rooted vascular aquatic plants in
1985. On the Chincoteague study area, widgeon grass (Ruppia marilima) and eel grass
Habltat suizabimy index Model 131l
(Zostera marina) were dominant vascular plants in estuarine waters. In our opinion, there was
no change in aquatic plant cover between 1985 and 1986.
In 1985, impoundment water levels were high and averaged approximately 0.3-0.6 m in depth.
Ruppia and Pofamogeton occurred on 13.7% of transect points; after weighting this sampling
by the relative areas of the pools, a value of 20.7% was estimated for V,. ln 1986, however,
refuge impoundments did not üll with rainwater until mid-December; Ruppia and Potamogeton
were negligible at the time of sampling, representing only 0.2% of transect points. During
both years, Eleocharis parvula was the dominant waterfowl food in refuge impoundments.
Vegetation survey data are on tile with the Chincoteague NWR.
In both 1985 and 1986, no plots sampled on tidal flats contained 2 300 clams/m'. We had
planned to use sieves if clam counts were high; however, the highest plot count during two
years was four. ln 1986, in fact, a total of four clams were counted in 100 sample plots.
Mercenaria mercenaria was the common clam; Tellina sp. and Tagelus sp. were infrequently
found on transects.
Fifty-four plots (20.8%) contained 2 750 snails/m' in 1985; only 18 plots (6.9%) contained 2
750 snails/mz in 1986 (V,). A Wilcoxon two-sample comparison suggested that Melampus snail
densities varied significantly between years (Z = -5.414, p < 0.0001). Mean snail densities
were 37.8/0.1 m' (n=260, SE=3.27) and 16.0/0.1m’
(n=260, SE=2.28) in 1985 and 1986, re-
spectively. Snail counts were different between four height classes of Spartina alternifolia
(Kruskall-Wallis X’=155.9, df=3, p < 0.0001; Table 35). Pairwise comparisons, using the
Wilcoxon two-sample test to separate means, suggested that snail densities in 21-40 cm, 41-60
cm, and <21 or >60 cm cordgrass were different (pS0.05). Snail densities in >60 cm
cordgrass tended to be lower than those in <21 cm cordgrass (p=0.082).
Spartina height differed between years (X'=25.4, df=3, p<0.001). Plots in 1985 contained
significantly more cordgrass in the 41-60 cm height class than expected (cell ;g“=6.40, df=1)
Habltat suitebamy Index Model 132
and significantly less cordgrass in the 0-20 cm class than expected (cell X'=4.32, df=1); the
opposite was true in 1986. This difference in cordgrass height may explain the difference in
snail counts between years. Marsh periwinkles (Littorina irrorata) and ribbed mussels
(Geukensia demissa) also were common gastropods in the saltmarsh; the mud dog whelk
(Nassarius obsoletus) was commonly found on flats and channel banks of high sill composi-
tion.
Discussion
Measurement of variables
Cartographic variables (V,, V2, V,) were measured as Lewis and Garrison (1984) suggested.
NWI maps proved to be easier to use than USGS maps because wetland habitat types were
designated with discrete boundaries; consequently, measurements could be replicated. We
have no suggestions for improvement.
The method used in this study for estimating submerged vegetative cover in subtidal waters
(V2) was practical; shallow subtidal waters covered almost 5400 ha and obtaining a represen-
tative sample from more conventional methods would be prohibitively time-consuming.
However, we suggest use of infrared film, extensive ground—truthlng, and randomization of
photo locations.
Lewis and Garrison (1984) suggested using an Ekman dredge to sample for clams. We found
that an Ekman dredge did not penetrate compacted sand and silt, nor did it consistently hold
a uniform sample. The 0.1 m' plot used in this study was adequate, although time-consuming.
As mentioned earlier, it would have been necessary to screen samples had clam counts ap-
Habltat Suitablllty Index Model 133
proached 300 clams/m'. Each transect (i.e., 10 plots) required 1-1 V; h to complete; as clam
counting is constrained by low tide, we were able to complete 2-3 transects per day (two
persons).
The 0.1 m' plot was a good method for estimating V,. lt is time consuming (1-1 V2 h/transect)
but we believe that the method provides an accurate estimate of snail densities. Snail
counting in the saltmarsh also is constrained by low tide but not to the degree that transects
on tidal tlats are; consequently, 3-4 transects were completed per day (two persons).
The five-point sampler proved to be a good method for sampling vegetative frequencies in
shallow impoundments; it was simple and efficient, although random stations may be more
appropriate than transects. Lewis and Garrison (1984) suggested using a plant dredge, which
would be appropriate for deeper water (>1 m); however, there is little value in sampling
deeper than a tive—point sampler can reach. Although black ducks have been known to dive
(Kutz 1940), diving is not a common foraging strategy.
Model output
Habitat Sultability Index models index habitat quality with a value that ranges from 0 - 1.0.
Members of the Habitat Evaluation Procedures Group and the Coastal Habitat Evaluation
Procedures Project (U.S. Fish and Wildlife Service 1984) stated that HSI models do not directly
measure carrying capacity; rather, the degree to which a model correlates with some meas-
ure of carrying capacity is directly related to the degree to which factors limiting that measure
have been identified and integrated into the habitat model. Consequently, validation tests
should use an independent measure that substantiates and quantifies the relationship be-
tween an animal and its habitat. Those authors suggested using habitat use data, abundance
data, or measures of "well being" (i.e., physiological condition) as independent measures.
Habitat Sultability Index Model 134
Variables for this HSI model were measured in 1985 and 1986 concurrently with a more com-
prehensive study of the wintering ecoiogy black ducks at Chincoteague. Consequently, we
have access to habitat use data, time budget data, and carcass condition information, which
serve as independent measures of the accuracy of model output.
In 1985, the overall HSI value was estimated to be 0.66; values for HSl[ow] and HSI[vw] were
0.56 and 0.76, respectlvely. ln 1986, the overall HSI value was estimated to be 0.56; values for
HSl[ow] and HSI[vw] were 0.56 and 0.56, respectlvely. A[ow] and A[vw] were 0.50 and 0.50,
respectively, for both years. Although we believe that model variables were well chosen by
Lewis and Garrison (1984), we suggest that the model is underestimating habitat quality on the
Chincoteague study area.
Analyses of carcasses collected on the study area indicated that black ducks were leaving
these wintering grounds in the spring of 1986 at least as fat and heavy as they entered them
in the fall (Chapter 3), suggesting that wintering conditions at Chincoteague were relatively
benign. Furthermore, based partially on Mid-Winter Waterfowl lnventories, the area between
Assateague Island and Wallops Island (coinciding with the study area) was ranked ürst in the
state of Virginia for acquisition in the Concept Plan for Preservation of Black Duck Wintering
Habitat (U.S. Fish and Wildife Service 1986). Clearly, the model is not accurately assessing
the quality of Chincoteague habitats.
On the Chincoteague study area, Ruppia and Potamogeton were not common forage items for
wintering black ducks. Esophageal and proventriculi contents data from 40 black ducks col-
lected on the study area during 1985-86 showed little evidence of Potamogeton and Ruppia
ingestion (Chapter 3). Seeds accounted for 45.9% of total dry weight and were found in 42.5%
of the digestive tracts. Vegetative material represented only 10.7% of total dry weight al-
though fragmented vegetation was found in 60% of the carcasses. We suggest that V, be
generalized to reflect the abundance of common waterfowl forages in local ponds and
Habitat Suitabllity Index Model 135
impoundments; restricting this variable to Ruppia and Potamogeton tends to underestimate
the value of this habitat type.
This model estimates both area and food value for subtidal water (V., V,). intertidal zones
(V,. V.), and creeks, ponds, and impoundments (V,. V.); however, it falls to specitically esti-
mate estuarine emergent vegetatlon although snail numbers are evaluated (V,). We suggest
including a new variable, V,. which would be an estlmate of the percentage of vegetated
wetlands that is represented by Spartina saltmarsh. This variable would be included in the
suitability equation for estuarine vegetated wetlands (Lewis and Garrison 1984) and all vari—
ables would be equally weighted (i.e., unweight V,):
(Sl, + Sl, + Sl, + Sl,) /4.
ln general, the model variables appear to be good indicators of habitat quality. With the two
changes suggested here, the model may have more applicability to wintering areas south of
Cape Cod. However, the ultimate decision as to the utility and effectiveness of this model
must be made on the basis of assessment in planning situations (U.S. Fish and Wildlife Service
1984).
Literature Cited
Kutz. H.L. 1940. The diving ability of the black duck. J. Wlldl. Manage. 4(1):19-20.
Lewis, J.C. and R.L. Garrison. 1984. Habltat suitability index models: American black duck
(wintering). National Coastal Ecosystems Team. Div. Biological Services, Research and
Development, U.S. Fish and Wildlife Service. FWS/OBS-82/10.68. 16pp.
Habltat Suitabillty Index Mudel 136
Lewis, J.C., M. Nelson, and J.D. Clark. 1984. A test of variables and equations potentially
useful in an HSI model for black duck coastal (wintering) habitat. U.S. Fish and Wildlife
Service. Unpubl. rep. 50pp.
U.S. Fish and Wildlife Service. 1984. Habitat Suitability Index model validatlons. Habitat
Evaluation Procedures Group, Ft. Collins, CO, and Coastal Habitat Evaluation Procedures
Project, Slidell, LA. 22pp.
Habitat Sultabillty Index Model 137
R)
28
S¤~
36
°
6S;
g¤
G3
—
'Y<:>
N6
ä—
Q
cY
C•
"r~
m
YÖ
ga
Y
"'sa
Y•~
"
'¤•
V
¤’
•.
co
6;{I
"
P
ES
gY
g
...-
„,
0
..O
s.
S
22
2
.
:~
"
zuao
'"'
U
°·:
Yvz
ci°
·¤=
‘é··
·¤¤
·¤ci
·=
-é
LQ
QY
oN
g
3‘°
coW
Y'
YN
g
,¤>
Qca
N
°
=*'
°?Y
6ZI
..4
nß
uID
c,
Q,
~¢
“G
°°°
v
an
•-•
cn\
gu
-„.
¤
c
Ex;
"ä
'
ram
„E
¤>
N"
••E
II)°
E3
0,,
0E
c:
.:1.
EE
1,m
E
°"2
¤·cu
Gg
Ö
E
gg
~¤"
Ssn
ID
··*—
6°
o0
:~
°0
8E
°N
9
M;
s.n
··E
*—
=•'
¤-_:
A1*6
2·¤
.
MQ
U
...•_
QE
G
.¤•-
3
...z
.¤E
3
Q3
.6E3
E$
äg
·¤
-
•·*¢¤
.-
gg
E;°
E5
0:
§
'*%.Z
Y,-
28
45&
‘öE
Wr-
Q
—
Ucn
C3
E*
5;
+-
g_
g-*5
g¤:
,>;·
-669.-
5¤
6E
E
_,cz
.¤E
ua
.¤
gn
gä
*'.
E
ig
LU
•
(3
E°
Q
Y$
>
··
—g
••>
_S
)
“'f¤
E}>
<·°ä<
°°••E
ag
>{fu
138
Table 35. Mean saltmarsh snafl counts ln four heightclasses ol saltmarsh cordgrass at Chlncoteague,Vlrglnla, ln the fall ol 1985 and 1986. A
HEIGHT (cm) n SE SE
0-20 125 5.06 a' 2.24
21-40 261 44.30 b 3.38
41·60 85 16.21 c 3.47
> 60 39 0.87 a 0.49
‘NIeans with same Ietter are not signiticanfly different(p20.05) according to Wilcoxon two·sample test.Overall Kruskall-Wallis x_'= 155.9, df=3, p<0.0001.
139
SUMMARY
Wintering populations of black ducks (Anas rubripes) on the Atlantic Flyway have decllned
50% since 1954. To better understand their wintering ecology, we conducted a study at
Chincoteague, Virginia, during the winters of 1985-86 and 1986-87. Some recent research has
been conducted in Maine and Canada where wintering black ducks are restricted to open
rivers and coastal tidal zones; however, at Chincoteague, black ducks are not usually con-
strained by ice and have access to several habitat types. Objectives of this study were to
determine habitat use, quantify time and energy expenditure, and quantify changes in
endogenous energy reserves over winter.
Twenty-three female black ducks were radio·tracked between 15 December 1985-1 March 1986
on a 25,600 ha study area that included the Chincoteague NWR and adjacent tidal habitats
(Chapter 1). Juvenile black ducks used range and core areas 2-3 times larger than adults.
Adults used one core area while juveniles tended to use more than one. Refuge
impoundments were used during the day and the saltmarsh was used at night. Subtidal wa-
ters were used during perlods of icing. Log-linear modeling suggested that habitat use was
determined primarily by the day-night cycle and secondarily by the tide—ice interaction.
SUMMARY 140
Scan sampling techniques were used to quantify behaviors of flocks within refuge pools,
saltmarsh, and subtidal water habitats during both years (Chapter 2). Black ducks fed least
and rested most when in refuge pools during the day; conversely, they fed most and rested
least when in subtidal waters during the day. Nocturnal observations (with a night-vision
scope) indicated that black ducks were at least as active at night as they were during the day.
l suggested that black ducks were primarily feeding at night in tidal habitats and roosting
during the day in refuge pools.
Diurnal energy expenditure (DEE) within habitat was estimated by the conventional use of
energy coeflicents; DEE for the average duck at Chincoteague was derlved by weighting ex-
penditure within habitat by the proportion of time spent in all three habitats. Comparisons
with DEE estimates of black ducks wintering in Maine suggested that black ducks have similar
DEE at a given temperature whether in Maine or Virginia.
When flocks were disturbed, scan sampling continued (until birds moved out of sight or
llushed) to obtain a random sample of the response to disturbance. Disturbed tlocks spent
more time on alert and in modes of Iocomotion, and severely curtailed feeding. The mean rate
of energy expenditure for disturbed flocks approximated that of undisturbed llocks; however,
47% of disturbed flocks llushed, a behavior that expends 5-6 times more energy than other
behaviors.
Sixty-four black ducks were collected during early, mid, and late winter at Chincoteague in
1985-86 (Chapter 3). Whole carcass analysis indicated that black ducks were at least as fat
and heavy in the spring as they were in the fall. Comparisons with similar work in Maine
suggest that black ducks experience a negative energy balance after mid-winter, the extent
of which is determined by the severity of the winter. Regression models were derlved from
body weight and external measurements to predict physiological condition of live black ducks
(R’=0.63).
SUMMARY 141
The Habitat Suitability lndex (HSI) model for winterlng black ducks was evaluated during both
years (Chapter 4). Comparison of overall model output with food habits and carcass data
suggested that the model underestimated habitat quality at Chincoteague. l proposed that
V, be modified to include local waterfowl foods (rather than Ruppia and Potamogeton) and a
new variable, V,, be created that estimates the percentage of wetlands represented by
Spartina saltmarsh.
SUMMARY 142
Appendlx A. Summary of avallable macro-habltat categorles and assocl-
ated Natlonal Wetland Inventory types on the Chincoteague study area.