GRASSLAND BIRD RESPONSE TO DISKING/INTERSEEDING OF LEGUMES IN CONSERVATION RESERVE PROGRAM LANDS IN NORTHEAST NEBRASKA By LUCAS PAUL NEGUS Bachelor of Science University of Nebraska at Kearney Kearney, Nebraska 2002 Submitted to the Faculty of the Graduate College of the Oklahoma State University in partial fulfillment of the requirements for the Degree of MASTER OF SCIENCE May, 2006
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GRASSLAND BIRD RESPONSE TO
DISKING/INTERSEEDING OF LEGUMES IN
CONSERVATION RESERVE PROGRAM LANDS IN
NORTHEAST NEBRASKA
By
LUCAS PAUL NEGUS
Bachelor of Science
University of Nebraska at Kearney
Kearney, Nebraska
2002
Submitted to the Faculty of the Graduate College of the
Oklahoma State University in partial fulfillment of
the requirements for the Degree of
MASTER OF SCIENCE May, 2006
ii
GRASSLAND BIRD RESPONSE TO
DISKING/INTERSEEDING OF LEGUMES IN
CONSERVATION RESERVE PROGRAM LANDS IN
NORTHEAST NEBRASKA
Thesis Approved:
Craig Davis
Timothy O’Connell
Tim McCoy
A. Gordon Emslie Dean of the Graduate College
iii
ACKNOWLEDGEMENTS
I would like to thank the Nebraska Game and Parks Commission for funding this
project through a State Wildlife Grant. I would specifically like to thank Scott Wessel for
preparing the grant, as well as for providing guidance, advice, and all levels of support
for the project. I also thank Pheasants Forever for providing field equipment and funding
for the project. The Lower Elkhorn Natural Resources District also provided funding for
field technicians, for which I am very thankful. I am also thankful to the Oklahoma State
University Zoology Department for administering the funds for the project.
This project could not have been completed without the assistance and guidance
of many individuals. I sincerely thank my major advisor, Dr. Craig A. Davis, for
guidance, advice, and support through all aspects of this project. I truly appreciate the
assistance and advice my graduate committee members, Dr. Timothy O’Connell and Dr.
Tim McCoy, provided during the study. This project could not have been completed in
entirety without the help of my field technicians, Jamie Bachmann, Cassidy Goc, Jordan
Johnson, and Adam Schole. I am very thankful for their enthusiasm and tireless work
ethic, enduring early, wet mornings and hot afternoons with no complaints. I would also
like to thank the graduate students of the Zoology department for providing help and
support when needed, and especially for the friendship and many good memories. I
would particularly like to thank Sabrina Rust, who lovingly stuck by my side and
supported me in everything I did the last several years. I would like to thank my family
for all the support and visits, as well as my dog, Tyson, for putting up with city life for
iv
the last couple of years. Finally, I would like to thank my parents for not only letting me
stay at home once again during the summers, but also for instilling the love of the
outdoors in me at an early age and supporting me through everything I have done.
v
TABLE OF CONTENTS
Chapter Page ACKNOWLEDGEMENTS ...................................................................................... iii LIST OF TABLES .................................................................................................... vii LIST OF FIGURES ................................................................................................... ix
I. GRASSLAND BIRD RESPONSE TO DISKING/INTERSEEDING LEGUMES IN CONSERVATION RESERVE PROGRAM LANDS IN NORTHEAST NEBRASKA ...........................................................................................................1
Grassland Avifauna...............................................................................................1 Habitat Loss and Degredation..........................................................................1 Habitat Fragmentation .....................................................................................3 Conservation Reserve Program.............................................................................5 Justification ..............................................................................................................8 Objectives ..............................................................................................................12 Methods..................................................................................................................12 Study Area ..........................................................................................................12 Disking and Interseeding ....................................................................................13 Bird Abundance Surveys ....................................................................................15 Nest Searches and Monitoring ............................................................................15 Vegetation Sampling...........................................................................................16 Statistical Analysis..............................................................................................17 Results....................................................................................................................21 Grassland Bird Community ................................................................................21 Nesting Success ..................................................................................................23 Vegetation Characteristics ..................................................................................26 Vegetation Influences .........................................................................................27 Discussion ..............................................................................................................28 Conservation Implications and Management.........................................................41 Literature Cited ......................................................................................................46 APPENDICES ............................................................................................................85
vi
Appendix A............................................................................................................85 Appendix B ............................................................................................................87 Appendix C ............................................................................................................89
vii
LIST OF TABLES Table Page 1.1. Overall relative abundance, species richness, and species diversity of breeding
grassland birds in treatment and reference fields in Stanton County, Nebraska, 2004-2005. ....................................................................................................................61
1.2. Relative abundance (birds/transect) of breeding grassland birds that were observed
in >1% of surveys in treatment and reference fields in Stanton County, Nebraska, 2004-2005. ....................................................................................................................62
1.3. Relative abundance (birds/transect) of breeding grassland birds that were observed
in >1% of surveys in 3 portions of Conservation Reserve Program fields managed by disking/interseeding in Stanton County, Nebraska, 2004-2005...............................64
1.4. Number of nesting species, number of nests, and nest density (nests/ha) of grassland
birds in treatment and reference fields in Stanton County, Nebraska, 2004-2005 .......66 1.5. Nest success probabilities for incubation, nestling, and overall nesting period for all
bird species in treatment and reference fields in Stanton County, Nebraska, 2004-2005...............................................................................................................................67
1.6. Nest success probabilities for all bird species, dickcissels, and red-winged
blackbirds in Conservation Reserve Program fields in Stanton County, Nebraska, 2004 and 2005...............................................................................................................68
1.7. Vegetation characteristics of successful and unsuccessful nests of all grassland bird
species in Conservation Reserve Program fields in Stanton County, Nebraska, 2004-2005. ....................................................................................................................69
1.8. Vegetation characteristics of successful and unsuccessful dickcissel nests in
Conservation Reserve Program fields in Stanton County, Nebraska, 2004-2005 ........70 1.9. Vegetation characteristics of successful and unsuccessful red-winged blackbird
nests in Conservation Reserve Program fields in Stanton County, Nebraska, 2004-2005. .............................................................................................................................71
1.10. Vegetation characteristics of successful and unsuccessful grasshopper sparrow nests
in Conservation Reserve Program fields in Stanton County, Nebraska, 2004-2005....72
viii
1.11. Vegetation characteristics of successful and unsuccessful bobolink nests in
Conservation Reserve Program fields in Stanton County, Nebraska, 2004-2005 ........73 1.12. Vegetation characteristics of treatment and reference fields in Conservation Reserve
Program fields in Stanton County, Nebraska, 2004-2005 ............................................74 1.13. Vegetation characteristics of 3 portions of Conservation Reserve Program fields
managed by disking/interseeding in Stanton County, Nebraska, 2004-2005 ...............75 1.14. Logistic regression models for vegetation variables that best predicted grassland
bird presence in treatment sites in Stanton County, Nebraska, 2004-2005 ..................77 1.15. Logistic regression models for vegetation variables that best predicted grassland
bird presence in reference sites in Stanton County, Nebraska, 2004-2005 ..................78
ix
LIST OF FIGURES
Figure Page 1.1. Location of study area (represented by black box) in Stanton County, Nebraska........79 1.2. Distance frequency histograms for all species, dickcissels, grasshopper sparrows,
and bobolinks in treatment and reference fields in Stanton County, Nebraska, 2004 and 2005........................................................................................................................81
1.3. Mean (+ S.E.) nest density (nests/ha) for all species combined for 0- (n = 2), 1- (n =
4), and 2-year (n = 2) post treatment and no treatment (n = 11) nest search plots in Conservation Reserve Program fields in Stanton County, Nebraska, 2004 and 2005. Means with different letters are significantly different (P < 0.05) ...............................83
1
CHAPTER I: GRASSLAND BIRD RESPONSE TO DISKING/INTERSEEDING OF LEGUMES IN CONSERVATION RESERVE PROGRAM LANDS IN
NORTHEAST NEBRASKA
INTRODUCTION
Grassland Avifauna
Throughout the Midwest, grassland bird populations are declining faster than any
other group of birds (Samson and Knopf 1994). From 1969 to 1991, grassland bird
populations in Illinois, Minnesota, Wyoming, Nebraska and Missouri declined from 24 to
91% (Samson and Knopf 1994). These declines have been attributed mainly to the loss
of prairie habitat. Samson and Knopf (1994) estimated that as little as 1% of native
prairie habitat remains in the Midwest. Unfortunately, the prairie that remains often
exists in small fragments and receives insufficient management. Additionally, modern
agricultural practices that favor reduced crop diversity and increased field sizes may
contribute to declines in grassland bird numbers (Best et al. 1998).
Habitat loss and degradation—Habitat loss is the primary cause for declines in
grassland bird numbers. There were approximately 162 million ha of prairie in the Great
Plains prior to European settlement, with the Tallgrass Prairie Ecoregion constituting
approximately 60 million of these hectares (Samson and Knopf 1994, Steinauer and
Collins 1996). Today, most of the tallgrass prairie has been plowed and converted to
agricultural lands, with losses as high as 99.9% in some states (Steinauer and Collins
1996). Habitat loss is not the only factor contributing to the decline in grassland birds.
2
Improper or inadequate management of remaining grasslands may also play a role in
grassland bird declines. Fire historically played a major role in the maintenance of
prairies. Periodic fires (every 2-5 years) set by lightning or Native Americans restricted
woody vegetation from encroaching into the prairies and increased plant species diversity
(Steinauer and Collins 1996). Since European settlement, fires have been suppressed
allowing woody vegetation to encroach on and often dominate prairies. The importance
of fire is evident by the response of grassland birds to this disturbance factor. Dechant et
al. (2003) recommended burning every 2-4 years to improve habitat for grasshopper
sparrows (Ammodramus savannarum). Bobolinks (Dolichonyx oryzivorus) also respond
positively to properly timed burns (2-4 yrs) (Herkert 1994). Johnson and Temple (1990)
found lower rates of nest depredation on grasshopper sparrow nests in recently burned
areas in Minnesota.
Many grasslands are included in farming and ranching operations, often to the
detriment of the ecological attributes of those grasslands. Specifically, many agricultural
grasslands and forage crops are mowed or hayed annually, with entire fields being cut in
mid-summer during the peak of nesting season for many grassland birds. Annual
mowing during the breeding season results in high rates of nest failure for dickcissels
(Spiza americana; Frawley and Best 1991). In a study in New York, mowing during the
breeding season accounted for 51% of nest failures for bobolinks (Bollinger et al. 1990).
Annual mowing of entire fields provides habitat for only a select few grassland bird
species, limits changes in vegetation structure, and promotes grass succession (Horn and
Koford 2000, McCoy et al. 2001a). Improper grazing strategies also adversely affect
grassland birds (Zimmerman 1997). The primary impact of grazing is reduction or
3
elimination of above-ground vegetation. Season-long grazing or intensive grazing during
the nesting period reduces vegetation height and density at a critical period, resulting in
reduced avian abundance and productivity (Zimmerman 1997). For example, Swanson
(2003) reported that nesting success of savannah sparrows (Passerculus sandwichensis)
was significantly higher on ungrazed grasslands than on grasslands grazed continuously.
Temple et al. (1999) reported dickcissels were more abundant in ungrazed grasslands
than in continuously or rotationally grazed pastures in southwestern Wisconsin.
Habitat fragmentation—Habitat fragmentation may also be a contributing factor
to declining grassland bird numbers (Herkert 1994, Winter and Faaborg 1999). Johnson
and Igl (2001) defined habitat fragmentation in prairies as the division of large,
contiguous areas of prairie habitat into smaller patches isolated from one another. Three
effects of fragmentation are reduced patch-size, increased edge, and increased isolation
(Johnson and Igl 2001). Several studies have found decreasing patch size to have
negative effects on the presence and nest success of grassland birds (Herkert 1994, Helzer
and Jelinski 1999, Winter and Faaborg 1999, Johnson and Igl 2001). Johnson and Igl
(2001) found 6 of 15 grassland bird species consistently favored larger patches of habitat
over smaller pathces. Herkert et al. (2003) studied nest predation in relation to patch size
for 4 grassland bird species (dickcissel, grasshopper sparrow, Henslow’s sparrow
[Ammodramus henslowii], and eastern meadowlark [Sturnella magna]) and reported
predation rates of these species consistently declined with increasing patch size.
Moreover, predation rates were consistently lowest in prairies larger than 1,000 ha.
Increased edge caused by habitat fragmentation also increases brood parasitism by
brown-headed cowbirds (Molothrus ater). Brown-headed cowbirds, one of the most
4
common edge species in the Great Plains, seem to favor small grassland patches (Johnson
and Igl 2001). Nest productivity is reduced by cowbird parasitism because fewer host
young fledge from parasitized nests than non-parasitized nests (Johnson and Temple
1986). Johnson and Temple (1990) found brood parasitism increased with decreasing
distance to edge. It is speculated that brown-headed cowbirds are more effective near
edges because they use high perches in trees to locate the host’s nests (Johnson and
Temple 1990). Davis and Sealy (2000) observed that cowbird parasitism was highest in
small, irregularly shaped plots with high amounts of edge. Two proposed management
strategies that could reduce cowbird parasitism in grasslands are providing and creating
large tracts of grassland habitat and removing woody edges and woody vegetation from
grasslands (Johnson and Temple 1990, Davis and Sealy 2000, Koford et al. 2000).
The effects of habitat isolation are difficult to quantify. In the field of landscape
ecology, biologists attempt to label isolated habitats as source or sink habitats for animal
populations. A source population is a population in which fecundity is greater than that
required to maintain a stable population. Conversely, a sink population occurs if
fecundity is below the level that is required to maintain a stable population (Pulliam
1988). Although some grasslands have been identified as source or sink habitats for
grassland birds, critical size or specific characteristics of the grassland habitat that
influence source/sink status are not easily identified. Management recommendations
generally encourage large, diverse grasslands to benefit grassland birds, but exact sizes
and habitat conditions required by many species still remain unclear. Johnson and Igl
(2001) suggest that creating grassland habitat near existing grasslands, or establishing 1
large field rather than several small ones would benefit more grassland bird species than
5
creating small, isolated fields. Johnson and Igl (2001) also noted regional differences
may play a role in the development of management strategies (i.e., habitat requirements
in 1 region may not be applicable in another region). Identifying the regional differences
in habitat requirements and developing management strategies is an important component
in the conservation of grassland birds.
Conservation Reserve Program
With the tremendous losses of native prairie throughout the Midwest, surrogate
grasslands such as Conservation Reserve Program (CRP) fields have become increasingly
important to grassland wildlife. The CRP was established as a provision of the Food
Security Act of 1985 (1985 Farm Bill) and has been retained in both the 1996 and 2002
Farm Bills (U.S. Department of Agriculture 2003a). The original goals of CRP were to
reduce erosion and improve water quality of highly erodible cropland, with a co-equal
objective of creating and enhancing wildlife and fish habitat added in 1996 (Johnson and
Schwartz 1993a). CRP pays farmers annual rental payments to retire highly erodible
cropland from production and plant it to grasses, trees, or other perennial cover for 10-15
years (U.S. Department of Agriculture 2003a). CRP differs from previous farm set-aside
programs (e.g., the Payment in Kind Program) because it is a long-term program that
retires cropland for greater than 10 years by planting the cropland to permanent
vegetation providing substantial wildlife benefits (Hays et al. 1989).
In the Midwest, CRP lands have been found to be important to a variety of
grassland wildlife species. Game species such as ring-necked pheasants (Phasianus
colchicus; King and Savidge 1995), northern bobwhite (Colinus virginianus; King and
Savidge 1995), white-tailed deer (Odocoileus virginianus; Luttschwager and Higgins
6
1992) and ducks (Reynolds et al. 1994) all use CRP fields. A study by King and Savidge
(1995) revealed pheasant abundance was higher in areas with a high percentage of CRP
than areas with a low percentage of CRP, probably due to the increased nesting and
brood-rearing habitat. Reynolds et al. (1994) found duck nest success in CRP fields to be
as high or higher than that of cover planted specifically for duck nesting. Nest success
for ducks in CRP fields was 2-9% greater than nest success rates needed to maintain
stable populations.
Non-game grassland songbirds also benefit from CRP (Johnson and Schwartz
1993b, Patterson and Best 1996). Several studies have attributed increases or at least
stable trends in specific grassland bird species to CRP (Igl and Johnson 1995, Herkert
1998, Ryan et al. 1998). Herkert (1998) reported grasshopper sparrow population trends
that were negative in 13 mid-continental states prior to CRP were positive following CRP
enrollment in those states. Igl and Johnson (1995) attributed a rapid increase in Le
Conte’s sparrow (Ammodramus leconteii) in North Dakota to the increased nesting
habitat offered by CRP when favorable wet weather conditions occurred. In an analysis
of North American Breeding Bird Survey results before and after CRP, Reynolds et al.
(1994) concluded that 4 of 8 declining grassland bird species showed positive population
trends, with only 1 species continuing to decline. Not surprisingly, Ryan et al. (1998)
found relative abundance of birds in CRP fields was as much as 10 times higher than in
crop fields. In a similar study, Best et al. (1997) also found the abundance of birds to be
as much as 10.5 times higher in CRP than crop fields. Moreover, CRP fields supported 3
times more nesting species and 13.5 times the total number of nests than row crop fields.
7
Although CRP fields provide habitat for grassland birds, the size and connectivity
of fields influence their suitability for grassland birds. McCoy et al. (1999) determined
whether CRP lands in Missouri were source or sink habitats for grassland bird species.
They found that source-sink status differed among grassland bird species using CRP
fields. Among their results, they found that CRP fields were source habitats for
grasshopper sparrows, field sparrows (Spizella pusilla), eastern meadowlarks, and
American goldfinches (Carduelis tristis) and sink habitats for dickcissels and red-winged
blackbirds (Agelaius phoeniceus). McCoy et al. (1999) concluded that CRP created
“source” habitats for many species, especially where alternative-breeding habitat was in
poor condition or absent from the area. Other studies, however, have documented
declines in grassland bird populations associated with CRP, indicating these lands may
act as a sink habitat (Reynolds et al. 1994). Source/sink dynamics of CRP may be
important to the conservation of grassland birds and need to be investigated more
thoroughly.
Although CRP has benefited numerous wildlife species, the types of plantings
used in CRP fields can have a major effect on grassland bird species. Conservation
Reserve Program fields are planted to a variety of cover types, referred to as conservation
practices (CPs). Two of the most commonly implemented CPs are CP1, a cool-season
grass mix, and CP2, a warm-season grass mix. CP1’s are frequently dominated by
Taylor, S. 2002. Focus on pheasants- proposed activities. Nebraska Game and Parks
Commission. Unpublished report. Lincoln, Nebraska, USA.
Temple, S. A., B. M. Fevold, L. K. Paine, D. J. Undersander, and D. W. Sample.
1999. Nesting birds and grazing cattle: accommodating both on midwestern
pastures. Studies in Avian Biology 19:196-202.
__________. 2002. Dickcissel (Spiza americana). No. 703 in A. Poole and F. Gill,
editors, The birds of North America, The Birds of North America, Inc.,
Philadelphia, Pennsylvania, USA.
Thompson, F. R., III, W. Dijak, and D. E. Burhans. 1999. Video identification of
predators at songbird nests in old fields. Auk 116:259-264.
U.S. Department of Agriculture. 2003a. 2002 Farm Bill—Conservation Reserve
Program—long-term policy; interim rule. Federal Register, 7 CFR Part 1410.
_________. 2003b. The Conservation Reserve Program statistics.
http://www.fsa.usda.gov/dafp/cepd/crp.htm. Accessed 29 April 2004.
Vander Lee, B. A., R. S. Lutz, L. A. Hansen, and N. E. Mathews. 1999. Effects of
supplemental prey, vegetation, and time on success of artificial nests. Journal of
Wildlife Management 63:1299-1305.
59
Vickery, P. D. 1996. Grasshopper sparrow (Ammodramus savannarum). No. 239 in A.
Poole and F. Gill, editors, The birds of North America, The Academy of Natural
Sciences, Philadelphia, Pennsylvania, and The American Ornithologists’ Union,
Washington, D.C., USA.
Whitmore, R. C. 1981. Structural characteristics of grasshopper sparrow habitat.
Journal of Wildlife Management 45:811-814.
Whitmore, R. W., K. P. Pruess, and R. E. Gold. 1986. Insect food selection by 2-week-
old ring-necked pheasant chicks. Journal of Wildlife Management 50:223-228.
Wiens, J. A., and J. T. Rotenberry. 1981. Habitat associations and community structure
of birds in shrub steppe environments. Ecological Monographs 51:21-41.
__________. 1999. Nesting biology of dickcissels and Henslow’s sparrows in
southwestern Missouri prairie fragments. Wilson Bulletin 111:515-527.
__________, and J. Faaborg. 1999. Patterns of area sensitivity in grassland-nesting
birds. Conservation Biology 13:1424-1436.
__________, D. H. Johnson, and J. Faaborg. 2000. Evidence for edge effects on
multiple levels in tallgrass prairie. Condor 102:256-266.
__________, S. E. Hawks, J. A. Shaffer, and D. H. Johnson. 2003. Guidelines for
finding nests of passerine birds in tallgrass prairie. Prairie Naturalist 35:197-211.
__________, D. H. Johnson, and J. A. Shaffer. 2005. Variability in vegetation effects on
density and nesting success of grassland birds. Journal of Wildlife Management
69:185-198.
60
Yasukawa, K., and W. A. Searcy. 1995. Red-winged blackbird (Agelaius phoeniceus).
No. 184 in A. Poole and F. Gill, editors, The birds of North America, The
Academy of Natural Sciences, Philadelphia, Pennsylvania, and The American
Ornithologists’ Union, Washington, D.C., USA.
Zar, J. H. 1999. Biostatistical analysis, fourth edition. Prentice-Hall, Upper Saddle
River, New Jersey, USA.
Zimmerman, J. L. 1966. Polygyny in the dickcissel. Auk 83:534-546.
Zimmerman, J. L. 1982. Nesting success of dickcissels (Spiza americana) in preferred
and less preferred habitats. Auk 99:292-298.
__________. 1984. Nest predation and its relationship to habitat and nest density in
dickcissels. Condor 86:68-72.
__________. 1988. Breeding season habitat selection by the Henslow’s sparrow
(Ammodramus henslowii) in Kansas. Wilson Bulletin 100:17-24.
__________. 1992. Density-independent factors affecting the avian diversity of the
tallgrass prairie community. Wilson Bulletin 104:85-94.
__________. 1997. Avian community responses to fire, grazing, and drought in the
tallgrass prairie. Pages 167-180 in F. L. Knopf and F. B. Samson, editors.
Ecology and conservation of Great Plains vertebrates. Springer-Verlag, New
York, USA.
61
Table 1. Overall relative abundancea, species richnessb, and species diversityc of
breeding grassland birds in treatment and reference fields in Stanton County, Nebraska,
2004-2005.
a Mean abundance of all bird species from 3 sampling periods during each year. b Number of avian species observed in each field. c Shannon-Weiner species diversity index (Krebs 1999). d P = P-value for treatment (treatment vs. reference) and year (2004 vs. 2005) effects
from a 2-way analysis of variance. Interaction effects (treatment x year) were observed
for species richness (F1,28 = 4.47, P = 0.044). Means for species richness are reported
separately for each year.
Treatment (n = 8)
Reference (n = 8)
Pd
Year Mean S.E. Mean S.E. Treatment Year Overall abundance (no./transect)
2004-2005
4.49 0.25 2.93 0.21 <0.001 0.150
2004 10.13 0.48 6.00 0.53 <0.001 Species richness
2005 10.38 0.63 8.75 0.70 0.106 Species diversity
2004-2005
1.41 0.06 1.23 0.05 0.034 0.229
62
Table 2. Relative abundancea (birds/transect) of breeding grassland birds that were
observed in >1% of surveys in treatment and reference fields in Stanton County,
Nebraska, 2004-2005.
Treatment (n = 8)
Reference (n = 8)
Pc
Speciesb Year Mean S.E. Mean S.E. Treatment Year DICK 2004
2005
1.81
2.29
0.26
0.22
0.60
0.61
0.11
0.12
0.008
<0.001
GRSP 2004 2005
1.29
0.47
0.15
0.09
1.04
0.96
0.15
0.10
0.261
<0.001
BOBO 2004- 2005
0.57
0.09 1.44 0.16 <0.001 0.917
RWBL 2004-2005
0.52 0.10 0.03 0.01 <0.001 0.920
COYE 2004-2005
0.22 0.04 0.03 0.01 <0.001 0.170
SEWR 2004-2005
0.07 0.03 0.09 0.04 0.484 0.186
WEME 2004 2005
0.26
0.04
0.07
0.02
0.04
0.04
0.03
0.02
0.015
1.000
HESP 2004-2005
0.01 0.01 0.08 0.03 <0.006 0.349
a Mean abundance from 3 sampling periods each year. b DICK = dickcissel, RWBL = red-winged blackbird, BOBO = bobolink, GRSP =
western meadowlark, and HESP = Henslow’s sparrow. c P = P-value for treatment (treatment vs. reference) and year (2004 vs. 2005) effects
from a 2-way analysis of variance. Interaction (treatment x year) effects occurred for
63
dickcissels (F1,260 = 5.13, P = 0.024), grasshopper sparrows (F1,260 = 8.55, P = 0.004), and
western meadowlarks (F1,260 = 5.29, P = 0.022).
64
Table 3. Relative abundancea (birds/transect) of breeding grassland birds occurring in
>1% of surveys in 3 portions of Conservation Reserve Program fields managed by
disking/interseeding in Stanton County, Nebraska, 2004-2005.
Disked-2003 (n = 8)
Disked-2004 (n = 8)
Undisked (n = 8)
Speciesc Year Mean S.E. Mean S.E. Mean S.E. All Species
2004 2005
7.96ab
3.88b
0.69
0.45
3.33b
6.08a
0.21
0.52
3.00b
2.71b
0.43
0.43 DICK
2004 2005
4.25a
2.42b
0.40
0.31
0.33b
3.75a
0.16
0.31
0.83b
0.71c
0.24
0.19 RWBL 2004
2005
1.75a
0.38a
0.41
0.15
0.04b
0.59a
0.04
0.20
0.13b
0.25a
0.09
0.11 BOBO 2004-
2005 0.41b 0.14 0.22b 0.14 1.09a 0.16
GRSP 2004 2005
0.75b
0.17b
0.22
0.08
2.00a
0.42ab
0.23
0.15
1.13b
0.83a
0.26
0.20 COYE 2004
2005
0.42a
0.25b
0.12
0.09
0.00b
0.58a
0.00
0.15
0.04b
0.00c
0.04
0.00 a Mean abundance from 3 sampling periods each year. b Means in rows with different letters were different (P < 0.05). c DICK = dickcissel, RWBL = red-winged blackbird, BOBO = bobolink, GRSP =
grasshopper sparrow, and COYE = common yellowthroat. d P = P-value for treatment (disked 2003 vs. disked 2004 vs. undisked) effects from a 2-
way analysis of variance. Treatment x year interaction effects occurred in all species
combined (F2, 138 = 16.76, P < 0.001), dickcissels (F2,138 = 47.98, P < 0.001), red-winged
blackbirds (F2,138 = 10.41, P < 0.001), grasshopper sparrows (F2,138 = 5.77, P = 0.004),
65
and common yellowthroats (F2,138 = 10.12, P < 0.001). Means are reported separately for
each year.
66
Table 4. Number of nesting species, number of nests, and nest density (nests/ha) of
grassland birds in treatment and reference fields in Stanton County, Nebraska, 2004-
2005.
Treatment (n = 6)
Reference (n = 6)
Year Mean S.E. Mean S.E. Number of species
2004 2005
5
8
--
--
4 9
--
-- Number of nests
2004 2005
100
106
--
--
12
29
--
-- Nest density (nests/ha)
2004- 2005
2.79 1.10 0.91 0.28
67
Table 5. Nest success probabilitiesa for incubation, nestling, and overall nesting period
for all bird species in treatment and reference fields in Stanton County, Nebraska, 2004-
2005.
a Determined using Mayfield (1975) method. b P = P-value for chi-square analysis of overall nest success probability (Dow 1978).
Treatment (n = 159)
Reference (n = 30)
Pb
Incubation(%)
Nestling(%)
Overall(%)
Incubation(%)
Nestling(%)
Overall(%)
All bird species
47.64 43.29 20.62 52.55 38.57 20.27
0.971
68
Table 6. Nest success probabilitiesa for all bird species, dickcissels, and red-winged
blackbirds in Conservation Reserve Program fields in Stanton County, Nebraska, 2004-
2005.
a Determined using Mayfield (1975) method. b DICK = dickcissel and RWBL = red-winged blackbird. c P = P-value for chi-square analysis of overall nest success probability (Dow 1978).
2004 (n = 93)
2005 (n = 96)
Pc
Speciesb Incubation(%)
Nestling(%)
Overall(%)
Incubation(%)
Nestling(%)
Overall(%)
All bird species
57.77 46.43 26.82 41.32 37.98 15.28 0.053
DICK 64.19 40.36 25.91 31.77 44.64 14.18 0.232
RWBL 52.81 51.12 27.00 41.94 23.52 9.87 0.045
69
Table 7. Vegetation characteristics of successful and unsuccessful nests of all grassland
bird species in Conservation Reserve Program fields in Stanton County, Nebraska, 2004-
2005.
Successful (n = 60)
Unsuccessful (n = 180)
Pa
Vegetation characteristic
Year Mean S.E. Mean S.E. Fate Year
Nest height (cm) 2004 2005
36.06
16.00
4.68
3.96
37.71
34.22
2.76
2.14
0.749
<0.001
Visual obstruction (dm)
2004 2005
6.55
3.84
0.47
0.34
6.79
5.69
0.29
0.20
0.649
<0.001
Litter depth (cm) 2004-2005
1.95 0.24 1.64 0.13 0.036 <0.001
Maximum vegetation height (cm)
2004 2005
100.93
67.12
5.46
3.99
100.44
87.79
2.79
2.20
0.690
<0.001
Forb (%) 2004-2005
34.00 4.47 47.71 2.71 0.001 <0.001
Grass (%) 2004-2005
49.50 3.66 41.96 2.23 0.015 <0.001
Dead material (%) 2004-2005
12.83 2.52 9.21 1.15 0.057 0.010
Bare ground (%) 2004-2005
4.17 1.14 1.57 0.39 0.602 <0.001
a P = P-value for fate (successful vs. unsuccessful) and year (2004 vs. 2005) effects from
2-way analysis of variance. Interaction (fate x year) effects occurred in maximum
vegetation height (F1,236 = 8.19, P = 0.005), nest height (F1,234 = 5.55, P = 0.019), and
visual obstruction (F1,236 = 5.48, P = 0.020). Means are reported separately for each year
for these variables.
70
Table 8. Vegetation characteristics of successful and unsuccessful dickcissel nests in
Conservation Reserve Program fields in Stanton County, Nebraska, 2004-2005.
Successful (n = 20)
Unsuccessful (n = 62)
Pa
Vegetation characteristic
Year Mean S.E. Mean S.E. Fate Year
Nest height (cm) 2004-2005
31.25 3.64 33.31 1.73 0.171 0.002
Visual obstruction (dm)
2004-2005
6.80 0.50 6.46 0.24 0.560 <0.001
Litter depth (cm) 2004-2005
1.31 0.37 1.40 0.24 0.438 <0.001
Maximum vegetation height (cm)
2004 2005
112.62
72.86
6.27
7.23
102.27
89.80
4.12
3.03
0.148
0.043
Forb (%) 2004-2005
60.50 7.27 56.77 4.29 0.751 0.005
Grass (%) 2004-2005
31.00 5.75 37.10 3.77 0.928 0.006
Dead material (%) 2004 2005
0.00
12.86
0.00
7.14
2.31
6.11
1.28
1.34
0.213
0.123
Bare ground (%) 2004-2005
3.00 2.52 1.45 0.64 0.755 0.032
a P = P-value for fate (successful vs. unsuccessful) and year (2004 vs. 2005) effects from
2-way analysis of variance. Interaction (fate x year) effects occurred in maximum
vegetation height (F1,78 = 6.26, P = 0.014) and dead material cover (F1,78 = 4.09, P =
0.047). Means are reported separately for each year for these variables.
71
Table 9. Vegetation characteristics of successful and unsuccessful red-winged blackbird
nests in Conservation Reserve Program fields in Stanton County, Nebraska, 2004-2005.
Successful (n = 18)
Unsuccessful (n = 86)
Pa
Vegetation characteristic
Year Mean S.E. Mean S.E. Fate Year
Nest height (cm) 2004-2005
55.17 4.14 49.37 1.95 0.483 0.257
Visual obstruction (dm)
2004-2005
6.94 0.40 7.04 0.20 0.226 0.003
Litter depth (cm) 2004-2005
1.39 0.40 1.19 0.15 0.031 <0.001
Maximum vegetation height (cm)
2004-2005
111.61 4.21 103.88 1.70 0.903 <0.001
Forb (%) 2004-2005
41.11 6.36 56.98 3.39 0.013 0.041
Grass (%) 2004-2005
53.89 6.67 37.67 3.12 0.007 0.030
Dead material (%) 2004-2005
1.11 0.76 4.42 0.80 0.281 0.078
Bare ground (%) 2004-2005
4.44 2.46 1.41 0.44 0.912 0.005
a P= P-value for fate (successful vs. unsuccessful) and year (2004 vs. 2005) effects from
2-way analysis of variance. No interaction (fate x year) effects occurred.
72
Table 10. Vegetation characteristics of successful and unsuccessful grasshopper sparrow
nests in Conservation Reserve Program fields in Stanton County, Nebraska, 2004-2005.
Successful (n = 7)
Unsuccessful (n = 12)
Pa
Vegetation characteristic
Mean S.E. Mean S.E. Fate
Nest height (cm) 0.00 0.00 0.00 0.00 --
Visual obstruction (dm)
1.86 0.18 2.45 0.23 0.093
Litter depth (cm) 2.04 0.73 3.08 0.36 0.167
Maximum vegetation height (cm)
47.54 3.56 51.17 3.57 0.513
Forb (%) 0.00 0.00 0.83 0.83 0.461
Grass (%) 61.43 7.04 60.83 4.68 0.943
Dead material (%) 30.00 9.51 38.33 5.20 0.412
Bare ground (%) 11.43 5.95 0.83 0.83 0.055
a P = P-value for nest fate effects from 1-way analysis of variance.
73
Table 11. Vegetation characteristics of successful and unsuccessful bobolink nests in
Conservation Reserve Program fields in Stanton County, Nebraska, 2004-2005.
Grass (%) 70.00 5.77 65.00 5.67 0.549 Dead material (%) 32.86 7.14 36.25 7.30 0.747
Bare ground (%) 0.00 0.00 2.50 1.64 0.179
a P = P-value for nest fate effects from 1-way analysis of variance.
74
Table 12. Vegetation characteristics of treatment and reference fields in Conservation
Reserve Program fields in Stanton County, Nebraska, 2004-2005.
Treatement (n = 8)
Reference (n = 8)
Pa
Vegetation characteristic
Year Mean S.E. Mean S.E. Treatment Year
Visual obstruction (dm)
2004 2005
3.04
4.11
0.15
0.08
2.67
3.21
0.07
0.05
0.032
<0.001
Litter depth (cm) 2004 2005
1.51
1.98
0.11
0.10
3.34
2.82
0.09
0.09
<0.001
<0.001
Maximum vegetation height (cm)
2004 2005
57.60
73.78
1.91
1.16
57.46
54.30
1.03
0.56
0.966
<0.001
Forb (%) 2004-2005
23.80 1.29 1.43 0.32 <0.001 0.407
Grass (%) 2004-2005
41.81 1.16 63.93 0.85 <0.001 <0.001
Dead material (%) 2004 2005
27.36
23.06
1.46
1.10
48.13
30.51
1.69
1.03
<0.001
<0.001
Bare ground (%) 2004 2005
25.00
3.96
1.70
0.51
2.03
0.83
0.37
0.27
<0.001
<0.001
a P = P-value for treatment (treatment vs. reference) and year (2004 vs. 2005) effects
from 2-way analysis of variance. Interaction (treatment x year) effects occurred in
horizontal visual obstruction (F1,1040 = 8.65, P < 0.001), litter depth (F1,1040 = 30.17, P <
0.001), maximum vegetation height (F1,1040 = 61.70, P < 0.001), percent dead material
(F1,1040 = 25.20, P < 0.001), and percent bare ground (F1,1040 = 47.13, P < 0.001).
75
Table 13. Vegetation characteristics of 3 portions of Conservation Reserve Program
fields managed by disking/interseeding in Stanton County, Nebraska, 2004-2005.
Disked-2003 (n = 8)
Disked-2004 (n = 8)
Undisked (n = 8)
Vegetation characteristics
Year Mean S.E. Mean S.E. Mean S.E.
Visual obstruction (dm)
2004 2005
5.44aa
4.70a
0.26
0.13
0.50c
4.31b
0.08
0.17
3.17b
3.32c
0.10
0.09
Litter depth (cm)
2004 2005
0.34b
2.33b
0.05
0.19
0.39b
0.71c
0.06
0.10
3.80a
2.89a
0.12
0.15
Maximum vegetation height (cm)
2004 2005
90.31a
81.79a
2.38
1.98
23.96c
80.72a
1.49
1.85
58.54b
58.83b
1.42
1.17
Forb (%) 2004 2005
58.44a
17.29b
2.96
1.98
16.15b
49.27a
2.36
3.20
0.42c
1.25c
0.25
0.60 Grass (%) 2004
2005
21.88b
59.90a
2.11
2.39
14.90c
29.27b
2.01
2.09
62.50a
62.40a
1.40
1.64 Dead material (%)
2004 2005
11.04c
19.48b
1.47
1.61
22.92b
14.48c
2.24
1.77
48.13a
35.21a
2.17
1.68 Bare ground (%)
2004 2005
19.48b
3.33b
1.70
0.78
53.54a
7.40a
2.88
1.16
1.98c
1.15c
0.72
0.44 a Means in rows with different letters were different (P < 0.05). b P = P-value for treatment (disked 2003 vs. disked 2004 vs. undisked) effects from a 2-
way analysis of variance. Treatment x year interaction effects occurred in all analyses
(horizontal visual obstruction [F2,570 = 104.12, P < 0.001]; litter depth [F2,570 = 81.33, P <
0.001]; maximum vegetation height [F2,570 = 170.57, P < 0.001]; percent forb [F2,570 =
76
128.05, P < 0.001], grass [F2,570 = 46.53, P < 0.001], dead material [F2,570 = 18.59, P <
0.001], and bare ground [F2,570 = 56.38, P < 0.001] cover).
77
Table 14. Logistic regression models for vegetation variables that best predicted
grassland bird presence in treatment fields in Stanton County, Nebraska, 2004-2005.
Variables were selected from a set of vegetation variables using a backward-elimination
western meadowlark, HESP = Henslow’s sparrow. b P(presence) = 1/ (1 + exp{ - [bo + b1(x)]}) where P(presence) was the probability that a
bird species was present, bo and b1 were intercept and slope coefficients, and x was the
predictor variable (vegetation variable), and Absence(x) = 1 – Presence(x). c forb = forb cover, grass = grass cover, dead = dead material cover, bare = bare ground,
vo = horizontal visual obstruction, max ht = maximum vegetation height, and litter =
litter depth. d P = P-value for Hosmer and Lemeshow goodness-of-fit test of overall model.
78
Table 15. Logistic regression models for vegetation variables that best predicted
grassland bird presence in reference fields in Stanton County, Nebraska, 2004-2005.
Variables were selected from a set of vegetation variables using a backward-elimination
routine.
Speciesa Fitted logistic modelbc Pd
DICK No Significant Model
--
RWBL -7.59 + 1.06 (litter)
0.914
GRSP No Significant Model
--
BOBO -7.76 + 0.09 (grass) + 0.08 (dead)
0.305
COYE -21.71 + 0.27 (max ht)
0.999
WEME No Significant Model
--
SEWR No Significant Model
--
HESP No Significant Model
--
a DICK = dickcissel, RWBL = red-winged blackbird, BOBO = bobolink, GRSP =
western meadowlark, HESP = Henslow’s sparrow. b P(presence) = 1/ (1 + exp{ - [bo + b1(x)]}) where P(presence) was the probability that a
bird species was present, bo and b1 were intercept and slope coefficients, and x was the
predictor variable (vegetation variable), and Absence(x) = 1 – Presence(x). c forb = forb cover, grass = grass cover, dead = dead material cover, bare = bare ground,
vo = horizontal visual obstruction, max ht = maximum vegetation height, and litter =
litter depth. d P = P-value for Hosmer and Lemeshow goodness-of-fit test of overall model.
79
Figure 1. Location of study area (represented by the black box) in Stanton County,
Nebraska.
80
NEBRASKA
81
Figure 2. Distance frequency histograms for all species combined, dickcissels,
grasshopper sparrows, and bobolinks in treatment and reference fields in Stanton County,
Nebraska, 2005.
82
Freq
uenc
yofo
bserv
ation
s
All species
0
0.1
0.2
0.3
0 10 20 30 40 50
Distance interval (m)
Bobolink
0
0.1
0.2
0.3
0.4ReferenceTreatment
Grasshopper sparrow
0
0.1
0.2
0.3
Dickcissel
0
0.1
0.2
0.3
0.4
0.5
83
Figure 3. Mean (+ S.E.) nest density (nests/ha) for all species combined for 0- (n = 2), 1-
(n = 4), and 2-year (n = 2) post treatment and no treatment (n = 11) nest search plots in
Conservation Reserve Program fields in Stanton County, Nebraska, 2004 and 2005.
Means with different letters are significantly different (P < 0.05).
84
0123456789
10
0 1 2 No treatmentYears post treatment
Nest
s/ha
A
AB
BB
85
APPENDIX A
Bird species observed in Conservation Reserve Program fields in Stanton County,
Mallard (Anas platyrhychos) X XAmerican goldfinch (Carduelis tristis) X X
Field sparrow (Spizella pusilla) X X
Killdeer (Charadrius vociferous) X
House sparrow (Passer domesticus) X
86
Species
Treatment Reference
Blue-winged teal (Anus discors) X X
Brown-headed cowbird (Molothrus ater) X X
Ring-necked pheasant (Phasianus colchicus) X X
European starling (Sturnus vulgaris) X X
Northern flicker (Colaptes auratus) X X
Northern harrier (Circus cyaneus) X X
Orchard oriole (Icterus spurious) X
American robin (Turdus migratorius) X
Cedar waxwing (Bombycilla cedrorum) X
Eastern meadowlark (Sturnella magna) X
Baltimore oriole (Icterus galbula) X
87
APPENDIX B
Percentage of each plant species used as a primary vegetationa support for nest placement
by the 4 most common nesting grassland bird species in Conservation Reserve Program
fields in Stanton County, Nebraska, 2004-2005.
Plant Species Dickcissel (n = 89)
Red-winged blackbird (n = 106)
Grasshopper sparrow (n = 19)
Bobolink (n = 15)
Yellow sweetclover (Melilotus officinalis)
36 52
Alfalfa (Medicago sativa)
17 9
Red clover (Trifolium pratense)
11 4
Mustard spp. (Brassica spp.)
2 9
Smooth brome (Bromus inermis)
21 14 84 100
Thistle spp. (Carduus spp.) or (Cirsium spp.)
9 4
Curly doc (Rumex crispus)
5
Kentucky bluegrass (Poa pratensis)
5
Orchard grass (Dactylis glomerata)
1 11
Nettle spp. (Urtica spp.)
1
Sunflower spp. (Helianthus spp.)
1
Milkweed spp. (Asclepias spp.)
1
Wild plum (Prunus americana)
1
88
Plant Species Dickcissel
Red-winged blackbird
Grasshopper sparrow
Bobolink
Chinese elm (Ulmus parvifolia)
1
a In addition to the primary plant species used for nest placement, 36% of red-winged
blackbirds and 39% of dickcissels used a secondary plant species to help support the nest.
Secondary plant species were most commonly alfalfa (25%), smooth brome (23%),
yellow sweetclover (22%), and red clover (18%).
89
APPENDIX C
Relative abundance and biomass of invertebrates in disked/interseeded and undisked
portions of Conservation Reserve Program fields in Stanton County, Nebraska, 2004.
Disked-2003 (n = 8)
Disked-2004 (n = 8)
Undisked (n = 24)
Pa
Mean S.E. Mean S.E. Mean S.E. Period TreatmentAbundance 176.00ab 63.38 192.88a 50.94 79.58b 21.07 0.11 0.05 Biomass 1.29ab 0.38 1.53a 0.59 0.64b 0.09 0.02 0.03
a P = P-value for period (1 vs. 2) and treatment (disked-2003 vs. disked-2004 vs.
undisked) effects from 2-way analysis of variance. No interaction (period x treatment)
effects occurred. b Means in rows with different letters were different (P < 0.05).
VITA
Lucas Paul Negus
Candidate for the Degree of
Master of Science
Thesis: GRASSLAND BIRD RESPONSE TO DISKING/INTERSEEDING OF LEGUMES IN CONSERVATION RESERVE PROGRAM LANDS IN NORTHEAST NEBRASKA
Major Field: Wildlife and Fisheries Ecology Biographical:
Personal Data: Born in Tilden, Nebraska, 1980 Education: Elkhorn Valley High School, 1998; Bachelors of Science from
University of Nebraska-Kearney in May, 2002; Masters of Science candidate at Oklahoma State University in May, 2006.
Experience: Fish and Wildlife Biologist, Nebraska Game and Parks
Commission, 2002-2003; Conservation Technician, Nebraska Game and Parks Commission, 1999-2002; Work Study, Nebraska Game and Parks Commission, 1998-2002; Family farm employee.
Professional Memberships: Member of National chapter, Nebraska, and
Oklahoma state chapters of The Wildlife Society, Pheasants Forever, Oklahoma State University Zoology Graduate Student Society, Oklahoma State University student chapters of The Wildlife Society and American Fisheries Society.
Name: Lucas Paul Negus Date of Degree: May, 2006 Institution: Oklahoma State University Location: Stillwater, Oklahoma Title of Study: GRASSLAND BIRD RESPONSE TO DISKING/INTERSEEDING OF
LEGUMES IN CONSERVATION RESERVE PROGRAM LANDS IN NORTHEAST NEBRASKA
Pages in Study: 89 Candidate for the Degree of Master of Science
Major Field: Wildlife and Fisheries Ecology Scope and Method of Study: Throughout the Midwest, grassland birds have been
declining faster than any other group of birds, with the main cause for these declines being the extensive loss of native prairies. During the last 25 years, surrogate grasslands, such as Conservation Reserve Program (CRP) lands, have become increasingly important as an alternative habitat for grassland birds. However, many CRP grasslands that once provided excellent habitat are now dominated by monoculture stands of grass that have reduced wildlife benefits. In summer 2000, the Nebraska Game and Parks Commission and Pheasants Forever partnered with the United States Department of Agriculture’s Farm Service Agency and Natural Resource Conservation Service to initiate a program that promotes disking and interseeding legumes in CRP to improve nesting and brood-rearing habitat for ring-necked pheasants (Phasianus colchicus). Disking and interseeding will also likely affect grassland birds, yet there has been no research on their response to this practice. The objectives of this study were to determine grassland bird abundance and nest-productivity in disked and interseeded CRP, evaluate vegetative responses to disking and interseeding, and provide management recommendations that may influence future farm bill policy regarding CRP grasslands.
Findings and Conclusions: Findings indicate experimental fields had higher overall avian
species richness, abundance, and diversity than reference fields. Dickcissels, red-winged blackbirds, and common yellowthroats were more abundant in treatment fields while bobolinks and Henslow’s sparrows were more abundant in reference fields. Nest densities in experimental fields were nearly 3 times greater than nest densities in reference fields. To increase grassland bird diversity and abundance, I recommend establishing an annual rotation of disking/interseeding to create a mosaic of vegetation types, while leaving portions of CRP fields undisked to accommodate species that don’t respond positively to management.