Technical Report HCSU-021 POPULATION ESTIMATES AND MONITORING GUIDELINES FOR ENDANGERED LAYSAN TEAL, ANAS LAYSANENSIS, AT MIDWAY ATOLL: PILOT STUDY RESULTS 2008–2010 Michelle H. Reynolds¹, Kevin W. Brinck², and Leona Laniawe¹ ¹U.S. Geological Survey, Pacific Island Ecosystems Research Center, Kilauea Field Station, Hawaii National Park, HI 96718 ²Hawai‘i Cooperative Studies Unit, University of Hawai‘i at Hilo, Pacific Aquaculture and Coastal Resources Center, P.O. Box 44, Hawai‘i National Park, HI 96718 Hawai‘i Cooperative Studies Unit University of Hawai‘i at Hilo Pacific Aquaculture and Coastal Resources Center (PACRC) 200 W. Kawili St. Hilo, HI 96720 (808) 933-0706 January 2011
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Technical Report HCSU-021
POPULATION ESTIMATES AND MONITORING GUIDELINES FOR ENDANGERED LAYSAN TEAL,
ANAS LAYSANENSIS, AT MIDWAY ATOLL: PILOT STUDY RESULTS 2008–2010
Michelle H. Reynolds¹, Kevin W. Brinck², and Leona Laniawe¹
¹U.S. Geological Survey, Pacific Island Ecosystems Research Center, Kilauea Field Station, Hawaii National Park, HI 96718
²Hawai‘i Cooperative Studies Unit, University of Hawai‘i at Hilo, Pacific Aquaculture and Coastal Resources Center, P.O. Box 44, Hawai‘i National Park, HI 96718
Hawai‘i Cooperative Studies UnitUniversity of Hawai‘i at Hilo
Pacific Aquaculture and Coastal Resources Center (PACRC)200 W. Kawili St.
Hilo, HI 96720(808) 933-0706
January 2011
The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the opinions or policies of the U.S. Government. Mention of trade names or commercial products does not constitute their endorsement by the U.S. Government.
Technical Report HCSU-021
POPULATION ESTIMATES AND MONITORING GUIDELINES FOR
ENDANGERED LAYSAN TEAL, ANAS LAYSANENSIS, AT MIDWAY ATOLL:
PILOT STUDY RESULTS 2008–2010
Michelle H. Reynolds¹, Kevin W. Brinck², and Leona Laniawe¹
¹U.S. Geological Survey, Pacific Island Ecosystems Research Center, Kīlauea Field Station,
Hawai'i National Park, HI 96718
² Hawai'i Cooperative Studies Unit, University of Hawai'i at Hilo, Pacific Aquaculture and
Coastal Resources Center, P.O. Box 44, Hawai‗i National Park, HI 96718
KEY WORDS
mark-resight population estimators, Laysan Duck, Midway Atoll, closed populations, Lincoln-
STUDY SITE ............................................................................................................................................................... 7 FIELD METHODS ........................................................................................................................................................ 7
Population monitoring ......................................................................................................................................... 7 Capture and marking ........................................................................................................................................... 9
STATISTICAL ANALYSES ............................................................................................................................................ 9 Lincoln-Petersen style abundance estimates ........................................................................................................ 9 Simple count index of population ....................................................................................................................... 10 Power to detect a decline ................................................................................................................................... 11 Intrinsic growth rate .......................................................................................................................................... 11
Lincoln-Petersen style abundance estimates ...................................................................................................... 11 Summary of resight statistics ............................................................................................................................. 14 Simple count index of population ....................................................................................................................... 16 Power to detect a decline ................................................................................................................................... 17 Intrinsic growth rate and carrying capacity ...................................................................................................... 17
MANAGEMENT GOALS ............................................................................................................................................. 17 BEST ESTIMATES ...................................................................................................................................................... 18
Power analysis ................................................................................................................................................... 18 Mark-recapture likelihood models ..................................................................................................................... 19 Simple index tracking ......................................................................................................................................... 19 Hybrid methods .................................................................................................................................................. 19 Mark-recapture model data collection ............................................................................................................... 20 Lincoln-Petersen style estimates ........................................................................................................................ 20 Indices ................................................................................................................................................................ 21
MONITORING STANDARDS ....................................................................................................................................... 21 Power ................................................................................................................................................................. 21 Continuous resights ............................................................................................................................................ 21 All-wetland counts and incidental resights ........................................................................................................ 22
SUGGESTIONS FOR MONITORING .............................................................................................................................. 22
INCIDENTAL RESIGHTS ............................................................................................................................................ 30 Possible Band Numbers, Letters, and Symbols .................................................................................................. 31 Permanent Bands ............................................................................................................................................... 31 Temporary Bands ............................................................................................................................................... 32 Aluminum Only .................................................................................................................................................. 32 Band Discrepancy .............................................................................................................................................. 32
PROCEDURE FOR STANDARDIZED RESIGHT SURVEY OF ALL WETLANDS ................................................................ 34 Materials Needed: .............................................................................................................................................. 34 Procedure ......................................................................................................................................................... .34 Double Counts.................................................................................................................................................... 37 Temporary Bands ............................................................................................................................................... 38 Resight Survey Data Entry ................................................................................................................................. 38
PROCEDURE FOR PILOT ATOLL-WIDE ALL-WETLANDS COUNT .............................................................................. 43 Atoll-wide All-Wetlands Count Data Entry ........................................................................................................ 44
ATTACHMENT 1. REVISED DATA SHEETS: ............................................................................................................... 47 Resight data sheet .............................................................................................................................................. 48
ATTACHMENT 2. MIDWAY ATOLL LAYSAN TEAL SURVEY START LOCATIONS AND DIRECTION OF TRAVEL TABLES
Population monitoring of Laysan Teal at Midway Atoll
4
EXECUTIVE SUMMARY
Accurate estimates of population size are often crucial to determining status and planning
recovery of endangered species. The ability to detect trends in survival and population size over
time enables conservation managers to make effective decisions for species and refuge
management. During 2004–2007, the translocated population of endangered Laysan Teal (Anas laysanensis; also Laysan Duck) was fitted with radio transmitters providing known (―gold
standard‖) measures of survival and reproduction. However, as the population grew, statistically
rigorous monitoring protocols were needed that were less labor intensive than radio telemetry. A
population die-off and alarmingly high number of carcasses (181) were recorded during a
botulism epizootic in August–October 2008, which further reinforced the need for effective
monitoring protocols since this endangered species is vulnerable to catastrophic population
declines. In fall 2008, we initiated a pilot study using standardized surveys with uniquely
marked birds to monitor abundance and estimate the population growth rate of the reintroduced
Laysan Teal. Since few birds carried marks (leg bands) after the 2008 botulism die-off (only
about 15% of the population), and standardized surveys were not yet implemented, the
magnitude of the die-off on the population size was unknown.
To learn more about this endangered species' status and develop monitoring protocols
useful to refuge managers and recovery planners in the U.S. Fish and Wildlife Service (USFWS),
we marked (banded) 252 new Laysan Teal for this pilot project. With skilled refuge staff and
trained volunteers, we conducted counts of marked, unmarked, and unknown birds during bi-
monthly surveys from Oct 2008 to Jan 2010. We recorded the identities of marked birds
observed, recovered carcasses, and then used the last date a bird was detected alive and the
median resight frequency to conclude if a bird was likely to be alive on a given survey date.
Using mark-resight data and individual resight frequencies, we produced a series of abundance
estimates from surveys that met accuracy criteria and approached ―closed population‖
assumptions. Since only one year of standardized, atoll-wide surveys were conducted, we
analyzed data selected from multiple surveys using Lincoln-Petersen (LP) estimates instead of
multi-year likelihood estimators. We adjusted surveys to account for unknown birds (e.g.,
swimming birds), temporary band loss, and described the frequency of double counting. Double
counting is an important consideration in the population estimate because we found a maximum
of 13% of marked birds were counted multiple times during a survey.
These survey protocols allowed us to estimate the species' post-fledging population
(combined adults and juveniles), and the methods are comparable to those used on Laysan
Island. The Laysan Teal population increased 91% from 247 (95% CI, 233–260) in 2007 to
439–508 in early 2010. There was no change from 2009 to 2010 indicating that there was no
population growth, however, our 2010 estimate should be considered preliminary since only one
month of 2010 resight data was used. We compared a series of direct counts to their
corresponding population estimates during 2008–2009 to evaluate if counts could serve as an
unbiased ―index‖ of population abundance. There was a moderate correlation between
abundance estimates and total birds counted (r2
= 0.51) during resight surveys but a low
correlation with all-wetland counts (r2
= 0.02). This indicated that using direct all-wetland
counts to predict abundance would result in confidence intervals on the order of ± 200 birds,
which is equal to 50% of the estimate. With such large confidence intervals, it would be unlikely
to detect annual changes in abundance or determine the magnitude of a catastrophic decline.
Reynolds, Brinck, and Laniawe
Population monitoring of Laysan Teal at Midway Atoll
5
To improve the Laysan Teal population estimates, we recommend changes to the
monitoring protocol. Additional years of data are needed to quantify inter-annual seasonal
detection probabilities, which may allow the use of standardized direct counts as an unbiased
index of population size. Survey protocols should be enhanced through frequent resights, regular
survey intervals, and determining reliable standards to detect catastrophic declines and annual
changes in adult abundance. In late 2009 to early 2010, 68% of the population was marked with
unique color band combinations. This allowed for potentially accurate adult population
estimates and survival estimates without the need to mark new birds in 2010, 2011, and possibly
2012. However, efforts should be made to replace worn or illegible bands so birds can be
identified in future surveys. It would be valuable to develop more sophisticated population size
and survival models using Program MARK, a state-of-the-art software package which uses
likelihood models to analyze mark-recapture data. This would allow for more reliable adult
population and survival estimates to compare with the ―source‖ Laysan Teal population on
Laysan Island. These models will require additional years of resight data (> 1 year) and, in some
cases, an intensive annual effort of marking and recapture. Because data indicate standardized
all-wetland counts are a poor index of abundance, monitoring efforts could be improved by
expanding resight surveys to include all wetlands, discontinuing the all-wetland counts, and re-
allocating some of the wetland count effort to collect additional opportunistic resights.
Approximately two years of additional bimonthly surveys are needed to validate the direct count
as an appropriate index of population abundance. Additional years of individual resight data will
allow estimates of adult population size, as specified in recovery criteria, and to track species
We thank E. Dominio, J. Shore, G. Shuman, M. Vekasy, and field biologists for
assistance. Matt Brown (USFWS Midway Atoll NWR Manager), Marilet Zablan (USFWS,
Assistant Field Supervisor for Endangered Species), Gordon Tribble (USGS Pacific Island
Ecosystems Research Center, Director), Holly Freifeld (USFWS, Vertebrate Recovery
Coordinator), John Klavitter (USFWS Midway Atoll NWR Biologist/Assistant Refuge
Manager), and Loyal Mehrhoff (USFWS Pacific Islands Fish and Wildlife Office Field
Supervisor) made this study possible. We thank reviewers R. Camp, J. Hatfield, and A.
McClung for comments and feedback which improved this document. Sarah Nash edited and
formatted this report. This study was funded by U.S. Fish and Wildlife Service‘s Ecological
Service‘s Pacific Islands Ecoregion, Midway Atoll NWR, and U.S. Geological Survey, Pacific
Island Ecosystems Research Center. Any use of trade, product, or firm names in this publication
does not imply endorsement by the U.S. Government.
Reynolds, Brinck, and Laniawe
Population monitoring of Laysan Teal at Midway Atoll
6
INTRODUCTION
Accurate estimates of population size are often critical to understanding population
dynamics, planning conservation actions, and evaluating responses to management (e.g., Johnson
et al. 2006, King et al. 2006, McCartney et al. 2006). The Laysan Teal (Anas laysanensis) is an
endangered species restricted to approximately 10 km2 on Midway Atoll and Laysan Island, and
is one of the most difficult bird species to monitor effectively in the Papahānaumokuākea Marine
National Monument (Sincock & Kridler 1977). This difficulty is due to the Laysan Teal‘s
tendency to hide in dense vegetation, reluctance to flush, and seasonal changes in observability
(Marshall 1992, Reynolds 2002). Mark-recapture is a useful method for estimating population
abundance for animals such as the Laysan Teal, which are difficult to find, but which can be
individually marked (banded) and resighted in the future.
The U.S. Fish and Wildlife Service (USFWS) Recovery Branch requested marked
population studies in 2008 to determine how best to monitor the species‘ abundance and
population status at Midway Atoll National Wildlife Refuge (hereafter the Refuge). USFWS
Recovery Criteria specified abundance benchmarks and population trends to downlist the species
from endangered to threatened. Monitoring standards required that each population of breeding
adults must be stable or increasing, and monitoring data should demonstrate an average intrinsic
growth rate (λ) not less than 1.0 over a period of ≥ 10 consecutive years to account for
population fluctuations (U.S. Fish and Wildlife Service 2009). Two approaches to calculating λ
are to conduct counts of the population at regular intervals to estimate average annual change or
to quantify demographic parameters such as survival and fecundity. Additionally, the Recovery
Criteria specified that only adult populations be used. Fledglings and juveniles are excluded
because adding these groups tends to overestimate the number and size of breeding populations,
thereby underestimating the risk of extinction (U.S. Fish and Wildlife Service 2009).
Before the marked population studies could begin in 2008, botulism (Clostridium botulinum) type C caused an unusual mortality event for Laysan Teal at Midway (Work et al.
2010). The magnitude of the population decline and the risk to the species was unknown since
no population estimate was determined prior to the die-off. As a result, the Refuge was
interested in detecting emerging catastrophic declines plus annual increases and decreases in
abundance of Laysan Teal (J. Klavitter and M. Brown, USFWS, pers. comm.). The Refuge was
also interested in detecting population responses to management actions, but did not have
specific monitoring standards or adaptive management goals for population responses (Stankey
et al. 2005).
Standards for detecting changes in population abundance should incorporate the
magnitude of change, a time frame for detecting that change, and a measure of statistical
significance (Skalski et al. 2005). An example monitoring standard is "to be 90% likely to detect
a decline that would halve the population in five years." Detecting a change in population
abundance requires the ability to separate a real change in abundance from the uncertainty
inherent in the estimation technique. Collecting data in ways that minimize the sampling error
maximizes the ability to detect a real change in the population abundance (Zar 1996, Seavy &
Reynolds 2009).
Reynolds, Brinck, and Laniawe
Population monitoring of Laysan Teal at Midway Atoll
7
The unique behavior of Laysan Teal makes surveying the population on Midway Atoll
challenging. The Laysan Teal exhibits nocturnal and crepuscular activity and secretive nesting.
Simple counts would likely underestimate abundance, because the proportion of the total
population observed during any count is unknown and would vary from survey to survey.
Although mark-resight surveys are more complex than simple counts, they are a more
appropriate technique for monitoring this species. Mark-resight methods allow for estimates of
abundance, survival, population growth rate, and other demographic parameters. Likelihood
population models require three years of mark-resight data, but we were able to use this single
year of data from the pilot study to estimate abundance and assess monitoring protocols for the
population at Midway Atoll. We also summarized USGS translocation post-release population
data (Reynolds et al. 2008) for this report to analyze the six year population trend at Midway
Atoll.
METHODS
STUDY SITE
Midway Atoll (28 12‘N and 177 22‘W) is located 1,930 km from Honolulu, Hawaii,
comprised of three islands (Sand, 452 ha; Eastern, 136 ha; and Spit, 6 ha), and protected as a
National Wildlife Refuge (NWR) within the Papahānaumokuākea Marine National Monument.
There are 14 small diverse wetlands on the Refuge totaling about two hectares. In addition to
supporting the re-introduced population of Laysan Teal, Midway Atoll provides breeding habitat
for approximately three million Pacific seabirds.
FIELD METHODS
Population monitoring From November 2008–November 2009, monitoring consisted of weekly atoll-wide
counts of Laysan Teal using two survey methodologies. The first survey methodology was used
to estimate population abundances (resight survey), and the second provided an index count
(called all-wetland counts; Fig. 1a, b) to be validated using marked population methods. Skilled
observers searched wetlands using 10x binoculars or a spotting scope (40-60x) to detect or read
coded leg-bands of all Laysan Teal visible between, on, and around the wetlands (Appendix 3).
Surveys were initiated approximately two hours before sunset or at sunrise—times when the
greatest number of Laysan Teal are concentrated at interior wetlands. The starting location and
direction of surveys were randomly varied to reduce spatial-temporal bias. This protocol was
similar to methods used on Laysan Island as described in Marshall (1992) and Reynolds and
Citta (2007).
Reynolds, Brinck, and Laniawe
Population monitoring of Laysan Teal at Midway Atoll
8
a)
b)
Figure 1a, b. Survey routes on Sand (a) and Eastern (b) islands. (Full-page versions of these maps are provided in
the Appendix, Attachment 3.)
Sunset Rolando
Monument
Reynolds, Brinck, and Laniawe
Population monitoring of Laysan Teal at Midway Atoll
9
Prior to this study, the U.S. Geological Survey also assisted the Refuge with post-release
monitoring of translocated birds using radio telemetry, and conducted opportunistic pilot surveys
of Sand Island‘s wetlands in January, February, May, and July–September in 2007. A morning
or evening resight survey was conducted on both Sand and Eastern islands in October and
November in 2007. Simultaneous atoll-wide resight surveys were conducted 1–2 times per
month in January and March 2008. We used these early data and data from this pilot study to
construct a time series of abundance estimates and evaluate the sampling to improve survey
methods. For detailed field methodology refer to the survey protocols (Appendix 3). Survey
protocols were updated based on pilot study results, and may be updated in the future based on
future results.
Capture and marking Laysan Teal were trapped at wetlands, in a variety of terrestrial habitats, and on roads
around Midway Atoll in November 2008, March–May 2009, and September–October 2009.
Most birds were caught at night using a flexible handheld net and headlamps or at crepuscular
periods using noose carpets. A numbered aluminum band was placed on one leg and a plastic
color band with alpha or numeric codes on the other leg of each bird. Nasal or wing marks,
commonly used in waterfowl marking, were inappropriate for this endangered species due to a
high risk of entanglement. All birds were released near their capture site. Prior to this study, all
individuals were marked through 2006, 56 juveniles were marked with permanent bands in 2007,
and 33 birds (6 juveniles, 27 adults) had temporary bands replaced in 2008–2009. The marked
population ranged from 20 birds in 2004 to 300–345 birds by 2009.
STATISTICAL ANALYSES
Lincoln-Petersen style abundance estimates We used a Lincoln-Petersen (LP) framework (Seber 1982) in which a known number of
birds are marked and released to mix freely in the population, so that during a later survey the
known number of marked birds and the ratio of marked to unmarked birds can be used to
estimate the total population abundance. The LP estimators tend to overestimate population
sizes, especially if few birds are seen or less than 20% of the population is marked (Robson &
Regier 1964; as of January 2010, 50–60% of the Laysan Teal at Midway were marked). We
chose this method because there was only one year of pilot study data, the estimator was simple
to calculate, and the same method had also been used on Laysan Island, permitting comparisons
of population abundance (Marshall 1992, Reynolds & Citta 2007, USFWS 2009).
The accuracy and precision of LP estimates depends upon six assumptions about the
animal population and the efficiency of data collection (Skalski et al. 2005):
1. The number of marks in the population is known
2. The population is geographically and demographically closed (no births, deaths,
immigration or emigration)
3. All animals have the same probability of being caught or sighted
4. Marking does not affect future detection
5. Animals do not lose their marks
6. All marks are correctly reported
It is important to note that the methods used to estimate the Laysan Teal population from
this pilot survey violate these assumptions in important ways, but we have devised methods to
Reynolds, Brinck, and Laniawe
Population monitoring of Laysan Teal at Midway Atoll
10
compensate for violations. Appendices 1 and 2 provide details. Where there was important
uncertainty (i.e., assumption #1), we presented a range of estimates that can be refined with
additional resight data.
Chapman‘s (1951) bias-corrected hypergeometric modification to the LP estimator is:
1)1)(1(ˆ
t
ttt m
nMN
where tN̂ is the population estimate, Mt is the total marked population, nt is the number of
animals counted, and mt is the number of marked animals counted (i.e., resighted), all at a given
time t. A nearly unbiased variance estimator (Seber 1982) is
)2()1(
))()(1)(1()ˆ(
2
tt
ttttttt mm
MnmMnMNVar .
To explore the quality of the data, we determined the total count and marked population
needed for a LP point estimate with 10% or 25% accuracy (assuming a population of 200–500
birds, the approximate range of our estimates)
using standards by Robson and Regier (1964;
Figure 2). Again, mt is the number of birds
resighted during a survey, and Mt is the number of
birds marked in the population (marked estimated
alive, MEA) at the time of the survey, as
estimated from banding and resight data
(Appendix 2). All calculations were carried out
in a Microsoft Excel workbook (Microsoft Corp.
2003; available upon request).
Simple count index of population We assessed the validity of using the total
number of birds observed in the resight surveys
and the all-wetland counts as an index of a more
detailed LP-style population estimate (Appendix
2) with a simple regression model. An index is a
population assessment technique that uses a
relative difference in abundance (e.g., from an
incomplete direct count) to describe changes in a
population (Lancia et al. 1996). Ideally, an index
is a constant ratio that can be calibrated with the
population estimate. Indices are different from
abundance estimators due to their inability to be
converted to absolute animal abundance, typically
because the necessary auxiliary data to make the
conversion are not collected (Skalski et al. 2005).
We describe the uncertainty in using a count
index to predict total Laysan Teal abundance in
more detail later in this paper. Because the
individual surveys varied in meeting accuracy and
Figure 2. Numbers of birds that need to be
marked and examined for marks on
subsequent surveys to estimate population
size within 10% (bold numbers) or 25%
(regular font) accuracy. This figure is
modified from Robson and Regier (1964).
The bold line represents combinations of
numbers of birds marked and numbers of
birds examined for marks that produce
population estimates accurate within 10% of
a population of 500 (line used in this study).
For example, if the population size (N) is
thought to be about 500, then you would
need to mark ~400 birds if your surveys
detected only 50–60 total birds. If your
surveys typically detected ~100 birds, 300
would need to be marked for estimates to be
accurate within 10%.
Number marked Mt
Reynolds, Brinck, and Laniawe
Population monitoring of Laysan Teal at Midway Atoll
11
precision standards, we used only the higher-quality LP estimates, where accuracy guidelines
(total marks plus birds observed > N̂ ) and precision guidelines (coefficient of variation of N̂ <
0.05) were met.
Using the estimated number of marked birds in the population and the actual number of
marks counted during resight surveys, we estimated the monthly probability of detecting an
individual and derived Horvitz-Thompson estimators based on detection probability (Thompson
1992), both for each month and also for morning vs. evening surveys. We compared those
estimators to LP-style abundance estimators using linear regression to test the strength of the
relationship between the two methods.
Power to detect a decline There are two major sources of variation in the annual estimate of the Laysan Teal on
Midway: actual fluctuation in bird abundance (process variation) and sampling error resulting
from random noise and inaccuracies in field data collection. In order to detect changes in
abundance over time, we would like to calculate a threshold outside which we are confident that
an observed trajectory represents a real trend in the population, beyond the fluctuations
introduced by sampling error.
Intrinsic growth rate We used abundance estimates from post-release radio telemetry and LP estimates from
resight surveys for a non-linear regression using program R (R Development Team 2009) to
estimate the intrinsic growth rate (λ) and model the potential carrying capacity on Midway Atoll.
Using a logistic growth model of the form
where N is the abundance and dtdN is the rate of population growth over time (the derivative of
abundance with respect to time), r is the natural logarithm of the growth rate (λ), adjusted for
density dependent growth, and K is the carrying capacity, or maximum population the
environment can support. Carrying capacity is likely confounded by events such as the botulism
epizootics in 2008 and 2009, and thus carrying capacity estimates are considered preliminary.
RESULTS
Lincoln-Petersen style abundance estimates There were 38 atoll-wide resight surveys between October 2007 and January 2010.
Seventeen of these resight surveys were considered high quality surveys and had enough total
resight observations to produce potentially precise (small uncertainty) and accurate (little or no
bias) estimates (Table 1), including one (23 October 2007) with enough information on known
age birds to produce a separate estimate for the number of juveniles. However, three of these
high-quality surveys (5, 12, and 19 November 2008) were made during the botulism outbreak,
when the mortality rate was high, thus violating the closed population assumption of the
Chapman estimator (i.e., marked birds classified as available to be counted may have been dead)
leading to biased estimates. All surveys in December 2009 did not use the standardized survey
NKNrdt
dN 1
Reynolds, Brinck, and Laniawe
Population monitoring of Laysan Teal at Midway Atoll
12
protocols, although the observer collected useful resight data for detecting individuals and
calculating median resight intervals (observer on different islands on different days). Estimates
that come closest to meeting LP model assumptions, meet accuracy and precision standards, and
were collected by experienced observers using standardized protocol are highlighted and
considered ―best estimates.‖
Table 1. Mark-resight Lincoln-Petersen estimates of Laysan Teal abundance, meeting the Robson and Regier (1964) standards for accuracy and precision and a
coefficient of variation < 0.05. We also show the results of the 23 October 2007 survey, the only data for 2007, and inferred pre-breeding abundance for
2008. Birds whose banding status could not be determined (e.g., swimming in turbid water) were assumed to be marked or unmarked in the same
proportions as those whose status could be determined. Best estimates—those which come closest to meeting LP model assumptions, while also meeting
accuracy and precision standards, and were collected by experienced observers using standardized protocol (two observers survey Sand and Eastern
simultaneously) —are in bold. The 2010 estimates are considered ―best preliminary estimates.‖ Surveys marked with * were conducted using different
methods, influencing the MEA (estimated marks alive). The 90% quantile vs. median detection intervals increase the time allowed to elapse before an
individual is considered missing (dead) and not available to be surveyed. Additional resights will allow for an improved MEA and LP estimate at the
median detection interval (see Appendix 2).
Resight survey results Using the median detection interval Using the 90th
An Incidental Resight is any band combination identified from a Laysan Teal (this protocol also
uses ―Laysan Duck‖ or LADU interchangeably) other than during an official (timed) Resight
Survey. Incidental resight information is valuable data used to determine the identification and
number of marked birds available to be counted. Data can be transcribed into a Laysan Teal
Incidental Resight Data Book. This data book or resighting data should be accessible in the
USFWS office. Include the following data:
Date, Time
Observer
Color Band and Color Band Symbol Right Leg (RL) and Left Leg (LL)
FWS or metal band (Right Leg or Left Leg and number), if not read DNR or ―did not read.‖
Most birds can be identified by their color band, and it is not necessary to read the aluminum
(AL) band unless the color band is missing or too faded.
Age Class of bird, if known (Table 6; L—duckling, AHY—after hatch year, ASY—after
second year)
Sex of bird, if known1
Location of sighting
Comments on band condition (worn or faded), occurrence of ducklings, injuries
OPTIONAL Behavior (was it sleeping, feeding)
OPTIONAL Any associated ducks or mates and the band combination (ID) of the other
duck(s)
1 Female Laysan Teal have a paler bill, often with small ―freckles‖ at the base. The legs are dull orange, and the
plumage may be lighter brown than males. Males have a black saddle on the bill with the sides of the bill deep
green. The legs are often bright orange, and males may have an upturned curled tail feather. The plumage on the
head may be darker brown.
Reynolds, Brinck, and Laniawe 31 Population monitoring of Laysan Teal at Midway Atoll
Table 6. Laysan Teal age class characteristics for Midway Atoll (Note Stage Ia–Ib ducklings are
very susceptible to mortality related to human disturbance).
Days Old Plumage Class Description
1 - 6 I a Bright ball of fluff; down bright and new; rounded
body; neck and tail not prominent
7 - 12 I b Fading ball of fluff; down fading
13 – 18 I c Gawky downy; down color and pattern faded; neck
and tail prominent; body long and oval
19 – 25 II a First feathers; feather begins on sides of body
26 – 35 II b
Mostly feathered; side view shows one half side and
flank feathered; down remains on nape of neck, back
and/or rump
36 – 45 II c Last down; little down on rump, neck, or back;
sheaths visible on erupted primaries, no eye ring
46 - 60 III a Feathered flightless = no down visible; flight feather
out of sheath but not fully developed
Flying 52 -63 III b Flies; still with brood
Flying
> 63 – 73 III c
Flies and more independent; small amt. white
plumage over eye; no sexual dimorphism
Hatched that
year > 73 HY / Fledgling
Independent; > 73 days until Jan 1 of following year.
Small; eye ring; glossy plumage; some sexual
dimorphism evident
Hatched
Previous Year SY
Glossy plumage; small eye ring; plumage often
distinguishable from Jan 1 until about March
Generic Adult AHY Any mature adult of unknown age
> 360 days ASY At least 50% plumage on head is white (general
guide-line for adults of unknown age)
Possible Band Numbers, Letters, and Symbols Use the following codes to record band colors and combinations or write out the colors and the
color of symbols on the color band. Please examine the string of sample color bands in the
biology office before attempting to record band resights.
Numbers: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
Letters: A, C, E, F, H, J, K, M, N, P, R, S, T, U, W, X, Y
Letters with Numbers: C1–C9, X1–X10
Two Letters: WA-WY, XA-XY
Symbols: *, #, $, <, >, ?, \ , /, &, +, -
Grooves: single (e.g., R/WG) or double (e.g., GN/2WG)
Permanent Bands Current permanent color band codes on Midway (Apr 2009):
AL = Federal aluminum
BK = Black with or without white letters, numbers or symbols (BK temporary bands without
numbers or symbols also occur)
BKY = Black with yellow numbers, letters, or symbols
BR = Brown with white numbers, letters, or symbols
Reynolds, Brinck, and Laniawe 32 Population monitoring of Laysan Teal at Midway Atoll
B = Blue (royal blue) with white numbers, letters, or symbols (Light Blue (LB) bands or Dark
Blue (DB) bands without symbols are also deployed) – if unfamiliar with codes please
write out the word Blu or Blue to distinguish from Black, or Brown
BY = Blue (royal blue) with yellow numbers, letters, or symbols
GN = Green with white numbers, letters, or symbols (Dark Green (DGN) and Light Green
(LGN) temporary color bands without symbols are also deployed)
GY = Grey with black numbers, letters, or symbols—if unfamiliar with codes write out the word
of the color and do not use the code GR which is confused with green
O = Orange with or without black letters, numbers, or symbols
R = Red with or without white letters, numbers, or symbols (be aware of Purple (PU) and
Fuchsia (FU) temporary bands that can be confused with red)
W = White with or without black letters, numbers, or symbols
WM = White band with mint green letters, numbers, or symbols
Y = Yellow with black numbers, letters, or symbols (Y temporary bands without numbers or
symbols also occur)
Bands with colored grooves or stripes are recorded as the band color, and the number and color
of grooves (e.g., Yellow with 1 Black Groove is coded as Y/BKG; Green with 2 White grooves
is coded as GN/2WG).
Temporary Bands Temporary color bands were deployed on young Laysan Teal in 2007 and rehabilitated birds
during the botulism epizootic in 2009. These typically have no symbol and no AL band. Colors
include all listed above plus: hot pink (HP), fuchsia (FU), purple (PU), light green (LGN), dark
green (DGN), light blue (LB), dark blue (DB). Many have fallen off so you may see a color
band on only one leg. It is important to try and specify temporary bands versus permanent
bands, especially those on birds that may have lost one of their temporary bands. Temporary
bands are coded using lower-case letters followed by ―-temp‖ (e.g., hot pink temporary is coded
as hp-temp; dark green temporary is coded as dgn-temp). These birds should be given
permanent bands to be included in population estimators.
Aluminum Only There are birds that only have an AL band with no color band. Please try to identify the sex of
the birds and read the numbers on these bands for a positive ID. Use a spotting scope to reduce
disturbance to the birds, especially during duckling season. Do not approach the birds closer
than 30 m unless you are doing a resight survey or a botulism carcass search. Never approach a hen with ducklings. Leave the area quickly if a hen with young ducklings approaches you. It is
ok for birds without ducklings to approach observers closer than 30 m especially during the non-
breeding season. Due to possible color band loss or unrecorded removals, there may be more
birds with ―AL only‖ than noted in the Resight Reference (the reference file for all bird bands
used). Always attempt to read all AL only numbers.
Band Discrepancy If there is a band combination that has been resighted that is not in the Resight Reference (RR),
record the bird as observed, make a note of it and try to resight the bird again. Some band
combinations may be incorrect in the RR because they might have been transposed accidentally
Reynolds, Brinck, and Laniawe 33 Population monitoring of Laysan Teal at Midway Atoll
during banding. After several sightings of the same combination, the RR should be corrected
(notify [email protected], Leona Laniawe, or John Klavitter). List the date and
person that reported the observation from the field.
1 1–3 1–3 Light air Ripples without crests. Smoke drift indicates wind direction, still
wind vanes.
2 4–7 4–6 Light breeze Small wavelets. Crests of glassy
appearance, not breaking
Wind felt on exposed skin. Leaves rustle,
vanes begin to move.
3 8–12 7–10 Gentle breeze Large wavelets. Crests begin to
break; scattered whitecaps
Leaves and small twigs constantly moving,
light flags extended.
4 13–18 11–16 Moderate breeze Small waves w/ breaking crests.
Fairly frequent white horses.
Dust and loose paper raised. Small branches
begin to move.
5 19–24 17–21 Fresh breeze
Moderate waves of some length.
Many white horses. Small amounts
of spray.
Branches of a moderate size move. Small
trees in leaf begin to sway.
6 25–31 22–27 Strong breeze
Long waves begin to form. White
foam crests are very frequent. Some
airborne spray is present.
Large branches in motion. Whistling heard
in overhead wires. Umbrella use becomes
difficult. Empty plastic garbage cans tip
over.
7 32–38 28–33
High wind,
moderate gale,
near gale
Sea heaps up. Some foam from
breaking waves is blown into streaks
along wind direction. Moderate
amounts of airborne spray
Whole trees in motion. Effort needed to
walk against the wind.
8 39–46 34–40 Gale, fresh gale
Moderately high waves with
breaking crests forming spindrift.
Well-marked streaks of foam are
blown along wind direction.
Considerable airborne spray
Some twigs broken from trees. Cars veer on
road. Progress on foot is seriously impeded.
9 47–54 41–47 Strong gale
High waves whose crests sometimes
roll over. Dense foam is blown
along wind direction. Large amounts
of airborne spray may begin to
reduce visibility.
Some branches break off trees, and some
small trees blow over.
Construction/temporary signs and
barricades blow over.
10 55–63 48–55 Storm, whole
gale
Very high waves with overhanging
crests. Large patches of foam from
wave crests give the sea a white
appearance. Considerable tumbling
of waves with heavy impact. Large
amounts of airborne spray reduce
visibility.
Trees are broken off or uprooted, saplings
bent and deformed. Poorly attached asphalt
shingles and shingles in poor condition peel
off roofs.
11 64–72 56–63 Violent storm
Exceptionally high waves. Very
large paths of foam driven before
the wind, cover much of the sea
surface. Very large amounts of
airborne spray severely reduce
visibility.
Widespread damage to vegetation. Many
roofing surfaces are damaged; asphalt tiles
that have curled up and/or fractured due to
age may break away completely.
12 73–83 64–71 Hurricane-force
Huge waves. Sea is completely
white with foam and spray. Air is
filled with driving spray, greatly
reducing visibility.
Very widespread damage to vegetation.
Some windows may break; mobile homes
and poorly constructed sheds and barns are
damaged. Debris may be hurled about.
Reynolds, Brinck, and Laniawe 38 Population monitoring of Laysan Teal at Midway Atoll
during the survey, record the total number of double-counted unique banded birds identified
atoll-wide on the data sheet.
Temporary Bands On the data sheet, include the number of Laysan Teal with: unique temporary bands (birds that
can be connected to a Link #; temporary bands were seen on BOTH legs), not unique temporary
bands (without Link #, only one leg was seen with a temporary band or both legs were seen with
only one temporary band), and the total number of temporary bands. Correct totals for double
counts; e.g., if bk-temp/bk-temp was recorded at both Catchment and Brackish, include one of
the two detections in the total.
Resight Survey Data Entry All data sheets should be scanned and saved electronically as a backup copy in case the hard
copy goes missing. Data should be entered by the observer as soon as possible after completing
the survey. Timely data entry avoids data backlogs, misplacement of data sheets, and provides
an opportunity for the observer to add data to incomplete data fields and decipher illegible
writing.
There are four Excel files that will be used with Laysan Duck Resight Survey data.
They are:
Midway Resight Reference—for reference only, containing all the band combinations in
use in the Laysan Duck population and data on those individuals (Figs. 7 and 9). Data
entry in this file is not covered here.
Midway All Resights—where all the information on each resighted individual is recorded
during the Resight Survey or incidental resights (Figs. 8 and 10).
Midway LADU Band—used during bird banding. This file can be used as a back-up for
band information if the current Resight Reference file is unavailable. Data entry in this
file is not covered here.
Midway LADU Survey Summaries: Standard Resight Summary tab—overall numbers of
birds for each island and atoll-wide including times of surveys and weather conditions
(Fig. 11).
1. The first step is to enter a resight record for each banded bird that was uniquely identified
by bands during the survey. This will verify that the band was read correctly and the age
and gender were appropriately recorded. To make the entry, open both the ―Midway
Resight Reference‖ (Fig. 7) and ―Midway All Resights‖ files (Fig. 8). Check with the
Laysan Duck data manager to verify that the Resight Reference file is current with all the
latest Laysan Duck banding data updates (newly banded birds, lost bands, changed bands,
unreadable bands, and mortalities). If the Midway Resight Reference is not current, data
entry should be delayed or the data manager should enter the data using the ―Midway
LADU Band‖ file. If the Midway Resight Reference is current, use this file to search for
the identity of the bird observed. To most easily search the Midway Resight Reference,
click on the small arrow located in the lower right corner of the header row cell
containing the field you would like to search under (Fig. 9). This is typically the band
observed on either the right or left leg. If the band was read accurately on the correct leg,
the band will be found. Once found, click on the correct band and the record for the bird
Reynolds, Brinck, and Laniawe 39 Population monitoring of Laysan Teal at Midway Atoll
or birds wearing this band will pop up. Use your mouse and highlight the information
contained in cells A to F, copy and paste it into the next available line in the cells under
the columns H to M in the Midway All Resights file (Fig. 10). Next, in the Midway All
Resights file type in all of the other information (date, time, etc.) pertaining to the
observation. Continue this process for all bands that were recorded during the survey.
Once all bands have been entered, save the file with a new name including observer
initials and the current date (e.g., Midway_All_Resights_MHR_19Jul2010.xls).
Figure 7. Laysan Duck Midway Resight Reference Excel file showing the header line and the first nine Laysan
Ducks currently surviving in Midway‘s population. Column A is the Midway Link # which is a unique
identifying number for each Laysan Duck. Columns B through D include the band on the right leg, band on the
left leg, and sex of the bird. Column E is the bird‘s age in 2009. Column F is the most recent aluminum
USFWS band number. Column G gives the origin of the bird, for example whether the bird was a translocated,
or founder, bird. Column H provides notes on the condition of the band, etc. Columns I and J list the location
and date the bird was last seen.
Reynolds, Brinck, and Laniawe 40 Population monitoring of Laysan Teal at Midway Atoll
Figure 8. Laysan Duck Midway All Resights file showing the header line and resight entries for Midway‘s population. Column A and B are the date and time of the
observation. Column C lists the observer initials. Columns D and E are the zone and the location where the bird was observed. Column F is the habitat type. Column G
is the unique link # for the bird observed. Columns H and I are the bird‘s bands for the right and left legs. Columns J and K list the sex and age. Column L (USGS #, i.e.,
USFWS number) is the current aluminum band the bird was wearing. Column M is used for recording numbers on the aluminum band that are read by the observer.
Columns N to R are used for recording information about the observed bird‘s mate. Column S is used for comments (this is where any behaviors can be recorded as well).
Column T lists the method of surveying that was used when the bird was observed.
Reynolds, Brinck, and Laniawe 41 Population monitoring of Laysan Teal at Midway Atoll
Figure 9. Using the Midway Resight Reference file to verify that a band was read correctly and locating the record for the bird. The small arrow in the lower right corner of
the header row for RLEG was clicked, allowing a search of available bands.
Figure 10. Midway All Resights file with the information pasted in that was copied from the Midway Resight Reference file.
Reynolds, Brinck, and Laniawe 42 Population monitoring of Laysan Teal at Midway Atoll
2. After all of the resights have been entered and all the bird bands, ages, and
genders have been confirmed, the next step is to enter the summarized survey
data. Open the ―Midway LADU Survey Summaries‖ file. Click on the ―Standard
Resight Summary‖ tab (Fig. 11). Three separate data lines will be entered
(assuming an atoll-wide survey was completed): one for Sand Island, one for
Eastern Island, and a third Atoll Wide line, which sums the results from Sand and
Eastern. If only one island was surveyed, only one line of data is entered for that
island surveyed. For the island surveyed, the date and island are entered in
columns A and B. In columns C and D, Atoll Wide or One Island and AM or PM
are written. Observer(s) initials are typed in column E. Start and end times and
time of sunset or sunrise are entered in columns F, G, and H, using a 24-hour
clock. Weather variables are recorded in columns I to K. Starting point
(Attachment 2), starting location, and direction of survey (clockwise or counter-
clockwise, entered as Clock or Counter) are entered in columns L to N. Next,
follow the data sheet and enter all the information cell by cell as indicated by the
header row from columns O to BR. If there is only one island to enter, proceed
with saving the file with a new name which includes the observer initials and date
(e.g., Midway_LADU_Survey_Summaries_MHR_19Jul2010.xls). If both islands
were surveyed, continue the data entry for the second island. Once the entry is
complete, add a third row of data which will sum the information for Sand and
Eastern islands. The date will be the same as the Sand Island survey date. Record
Atoll Wide for both columns B and C. Record morning or evening survey
(column D) and observer(s) initials (column E). Sum the survey information from
the two surveys for columns AE to AZ using the computer calculator, not by
hand. Once this is finished, the file is saved as indicated previously.
Figure 11. The Midway LADU Survey Summaries file, Standard Resight Summary tab showing the
headings and cells from columns A to N. Headings and columns are not shown for O to BR.
Reynolds, Brinck, and Laniawe 43 Population monitoring of Laysan Teal at Midway Atoll
PROCEDURE FOR PILOT ATOLL-WIDE ALL-WETLANDS COUNT
This survey will be discontinued in 2010. Resight surveys will be modified to
include all wetlands.
1. Twice per month, an atoll-wide All-Wetlands Count index should be conducted at
sunset or sunrise. The count must go no more than 15 minutes past the allotted
time for the data to be usable—aim to be efficient and finish on time.
On Sand Island every permanent and ephemeral wetland known should be
completed in 1 hour 45 minutes. Begin survey at sunrise or 1 hour 45 minutes
before sunset. Wetlands counted include Rusty Bucket Seep, Aviary Seep,
Six starting points and orders for Eastern Island Resight (and All-Wetlands Count)
(use in the following order, then restart):
Start point
Middle point Finish point
Resight
Survey
Date
Wetland
Count
Date
1 Sunset
Monument Rolando
2 Rolando Monument Sunset
3 Monument Rolando Sunset
4 Sunset Rolando Monument
5 Rolando Sunset Monument
6 Monument Sunset Rolando
Attachment 3. Maps illustrating survey routes on Sand Island & Eastern Island. Original Pilot Study: Sand Island Laysan Teal Standard Resight Survey Route