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At least 667 records · Page 37Linked to original sources
USGS2024

Body mass changes of dabbling and diving ducks wintering in California

Bird body mass is often used as an index of body condition and fluctuates throughout the year in response to environmental conditions and avian life-history events. We examined the body mass of 59,572 ducks representing 13 species (7 dabbling duck species and 6 diving duck species) harvested within the 3 regions of the Central Valley in California, USA (Sacramento Valley, Suisun Marsh, San Joaquin Valley). Data collection occurred in winter during 5 hunting seasons (2014–2015, 2015–2016, 2017–2018, 2018–2019, 2019–2020). For all species, age, and sex classes, the body mass of dabbling ducks varied temporally and was lowest at the end of the hunting season in late January, declining from the beginning of the hunting season in mid-October (northern pintail [ Anas acuta ]: −11.4% to −20.4%; northern shoveler [ Spatula clypeata ]: −3.5% to −17.3%; cinnamon teal [ Anas cyanoptera ]: −5.0% to −17.1%; American wigeon [ Mareca americana ]: −6.9% to −12.2%; American green-winged teal [ Anas carolinensis ]: −5.9% to −11.9%; mallard [ Anas platyrhynchos ]: −1.8% to −9.6%; gadwall [ Mareca strepera ]: −2.2% to −8.4%). As expected, adults (after hatch-year) were heavier than immature (hatch-year) birds (within males: 0.6–8.6%; within females: 0.1–6.6%) and males were heavier than females (within adults: 3.1–38.6%; within immatures: 5.4–33.5%) at the end of the hunting season in all species. Within dabbling duck species, body masses did not differ among regions at the beginning of the hunting season but were heavier in the Sacramento Valley (0.5–14.4%) than other areas by the end of the hunting season. In contrast, body masses of diving ducks did not vary substantially during the hunting season or among regions. Diving ducks demonstrated inconsistent changes in mass from the beginning to the end of the season (lesser scaup [ Aythya affinis ]: 3.4% to 12.3%; canvasback [ Aythya valisineria ]: 5.1% to 6.1%; bufflehead [ Bucephala albeola ]: −3.2% to 1.6%; ring-necked duck [ Aythya collaris ]: −4.9% to 2.6%; common goldeneye [ Bucephala clangula ]: −3.2% to −2.4%; ruddy duck [ Oxyura jamaicensis ]: −16.5% to 5.5%). The substantial temporal and spatial differences in dabbling duck body masses suggest that habitat quality (as measured by caloric value of the available food) or quantity may decline during winter and varies regionally within California's Central Valley.

California↗
USGS2024

Effects of release strategy, source population, and age on reintroduced scaled quail reproduction

Translocation is one strategy to reestablish populations of scaled quail ( Callipepla squamata ). Initial reproductive success post-translocation is important for establishing short-lived species such as quail, but factors influencing reproductive success are poorly understood. We evaluated the effect of source population and variation in delayed release strategy (1−9 weeks) on nest initiation and nest survival of wild-caught, translocated scaled quail. We trapped and translocated scaled quail in 2016–2017 from source populations in the Edwards Plateau and Rolling Plains ecoregions of Texas, USA, to a large contiguous (>40,000 ha) release site in Knox County, Texas. We used a multi-state mark-recapture model with state uncertainty to test for effects of release treatment, source population, age, release location, and year on nest initiation and survival. Increased length of holding time decreased re-nesting effort. Yearlings were more likely to initiate nests than adults and the probability of re-nesting was lower during the year with drought conditions. There was no effect of source population on any of the parameters we evaluated. Future scaled quail reintroduction efforts may benefit from prioritizing translocation of yearlings and conducting translocations when drought conditions are not forecasted.

Texas↗
USGS2024

Density estimation using spatial capture-recapture analyses: Application to vaccination of prairie dogs against sylvatic plague

Prairie dogs are notoriously difficult to enumerate, with previously methods including visual counts, mark-resight, burrow counts, and catch per unit effort. Unlike those methods, spatial capture-recapture (SCR) analyses allow for formal estimation of density along with associated estimates of uncertainty, detection probability, and the size of the average area over which an individual was detected during the study period (referred to as an activity center). Using SCR analyses, we compared density estimates as part of a field trial evaluating the effectiveness of an oral sylvatic plague vaccine in black-tailed prairie dogs ( Cynomys ludovicianus ), Gunnison's prairie dogs ( C. gunnisoni ), white-tailed prairie dogs ( C. leucurus ), and Utah prairie dogs ( C. parvidens ) at 11 study areas in the western United States. The study was designed as a matched pairs analysis that included 27 individual paired plots (54 plots), each consisting of a plot treated with vaccine baits and a plot treated with placebo baits. Overall, we captured >3,000 individuals each year on these plots, and recapture rates ranged from 5–87%. For black-tailed prairie dogs, density estimates ranged from 2.7 individuals/ha (95% CI = 2.2–3.3/ha) to 77.3/ha (63.2–94.4/ha), and for Gunnison's prairie dogs, estimates ranged from 11.7/ha (10.6–12.8/ha) to 15.4/ha (14.4–16.7/ha). White-tailed prairie dogs were at their lowest density (3.3/ha, 95% CI = 2.9–3.8/ha) during the first year of the study and their highest density (14.5/ha; 13.5–15.6/ha) during the last year of the study. Utah prairie dog density estimates ranged from a low of 4.0/ha (95% CI = 3.55–4.6/ha) to a high of 20.8/ha (16.8–25.8/ha). Best-fitting models of prairie dog density indicated increasing patterns of density over time on most study plots, negative effects of plague, and positive effects of vaccination. Finally, we found low correlations between catch per unit effort estimates from previous published literature at these sites and our densities estimates. Spatial capture-recapture estimates allowed us to consistently compare treatment effects across space and time, although some exceptions are noted where we observed significant movement between plots within a pair (3 pairs) and when trapping effort between plots or years was not consistent.

Arizona, Colorado, Montana, South Dakota, Utah, Wy↗
USGS2024

Sampling for disease surveillance: Assessing effects on blue-winged teal survival and recovery

Outbreaks of highly pathogenic avian influenza virus in wild animals highlight the need for disease surveillance in wild birds to improve our understanding of their role as reservoirs and dispersers, and potential threats to domestic poultry and wild bird populations. Surveillance for avian influenza varies in its approach, objectives, and coordination with other monitoring efforts. For waterfowl, a common host to avian influenza viruses, banding represents a concerted effort of capturing and marking thousands of individuals annually to estimate survival and harvest rates, but users of these data have generally taken a conservative approach to remove any banded birds from analyses that had a sample taken for disease surveillance during capture. We tested for differences in survival and encounter probabilities of blue-winged teal ( Spatula discors ) marked ( n = 21,702 teal) and sampled for disease surveillance ( n = 4,216) during the nonbreeding season in Louisiana, USA, from 2016 to 2023. Although we found no consistent effect of collecting biological samples on survival probability, including an additional test showing no detectable effects of sampling for disease surveillance with oropharyngeal and cloacal swabs versus sampling with swabs and a syringe-drawn blood sample, wide 95% credible intervals on the posterior survival estimates (mean 0.36 difference between upper and lower values across all year-sex-sampling groups; 0.44 for sampling type groups) indicated low statistical power to detect an effect. Seber recovery probability during the first interval following sampling was lower among birds sampled using swabs only, but we assume this stems from low sample sizes rather than an effect of collecting biological samples. Because recovery probabilities can vary as a function of individual covariates, we also examined direct recovery probabilities and observed no meaningful effect of disease surveillance sampling type but strong effects of capture date, suggesting the effect on Seber recovery probability may have been due to heterogeneity in exposure to natural and harvest mortality risks. Although we suggest that aligning disease surveillance sample collection efforts with landscape-scale waterfowl banding efforts may have little effect on observed demographic rates, additional studies with larger sample sizes are likely needed to provide the statistical power necessary to formally conclude no effect of biological sampling on survival probabilities.

Louisiana↗
USGS2025

Factors influencing daily nest survival rates of Aleutian terns in the Kodiak Archipelago, Alaska

The Aleutian tern ( Onychoprion aleuticus ) is a species of high conservation concern in Alaska, USA, owing to large declines at known breeding locations since the 1960s. The small population size and ephemeral behavior of this species have limited the collection of basic biological information and hindered the identification of potential drivers of this decline. Significant unknowns include the factors, and their relative importance, influencing nest survival. To investigate these questions, we estimated daily nest survival (DNS) for 148 nests from 5 breeding colonies during 2017 to 2020 in the Kodiak Archipelago, Alaska with 105 monitored using remote cameras. We used the nest survival model in program MARK to estimate DNS rates as a function of colony location, year, within-season time trends, vegetation cover and height, and 6 daily weather covariates. Our top model suggested that DNS rates increased with vegetation height, decreased as the season progressed, and included a significant interaction between year and colony. Average nest success (i.e., percent chance that a nest survived to hatch) over the 22-day incubation period varied by colony but was generally very low, averaging 1.2% (95% CI = 0–11%) in 2017–2018 to 14% (95% CI = 0.1–38%) in 2019–2020 across all colonies. The importance of year in the model suggests that a large-scale annual driver, like food availability, may have played an important role in this species' breeding success. A severe marine heatwave was present in the Gulf of Alaska during 2014–2016 and our results suggest that some effects of this anomalous event, such as reduced prey availability, lingered even after temperatures returned to normal. Additionally, the variation in DNS across colony locations indicated that local factors, such as predation pressure, may also drive significant variation in Aleutian tern productivity. These findings suggest that a combination of local factors and climate change may be important drivers of the >90% decline in Alaska's breeding population of Aleutian terns.

Alaska↗
USGS2025

Spatially explicit capture-recapture using fecal DNA to estimate elk population abundance and growth in western North Carolina, USA

In an effort to restore extirpated elk to their historical range, 52 elk were reintroduced to Great Smoky Mountains National Park (GRSM) in North Carolina, USA, during 2001 and 2002. Since their reintroduction, elk numbers have increased, and elk have extended their range beyond GRSM boundaries. We used spatially explicit capture-recapture (SCR) methods based on fecal DNA to identify individual elk and estimate population abundance ( N ), apparent survival ( φ ), per capita recruitment ( f ), and population growth rate ( λ ) in western North Carolina. We walked a series of transects during 3 winter field seasons (2020–2022) and collected elk pellets encountered along those transects. We created spatially explicit capture histories and incorporated those data into both closed and open population SCR models. The top performing closed SCR models for males and females estimated density by year and as a function of the scaled distance to the nearest field, with densities decreasing as the distance increased. Combined male and female N were 179 elk (95% CI = 149–215) in 2020, 220 elk (95% CI = 188–256) in 2021, and 240 elk (95% CI = 207–279) in 2022. The top open population model estimated both φ and λ as functions of sex and year. The estimate of φ for males was 0.682 (95% CI = 0.317–0.908) during 2020–2021 and 0.339 (95% CI = 0.152–0.596) during 2021–2022 and for females was 0.953 (95% CI = 0.830–1.000) during 2020–2021 and 0.829 (95% CI = 0.601–1.000) during 2021–2022. The annual population growth rate ( λ ) for males was 1.127 (95% CI = 0.806–1.575) during 2020–2021 and 0.811 (95% CI = 0.566–1.163) during 2021–2022 and for females was 1.559 (95% CI = 1.162–2.091) during 2020–2021 and 1.122 (95% CI = 0.876–1.437) during 2021–2022. Our elk abundance estimates in areas >300 m from fields were negligible, and we suggest that sampling only the areas in and adjacent to fields in the future will result in reliable but more cost-efficient population estimates. Confidence intervals for vital rate parameters were wide for our 3-year dataset, but continued annual pellet sampling will increase sample sizes for vital rate estimation and thus improve precision. If elk herd expansion on public lands is desired, we suggest habitat modification to establish open grasslands adjacent to forests.

North Carolina↗
USGS2011

Grizzly bear population vital rates and trend in the Northern Continental Divide Ecosystem, Montana

We estimated grizzly bear ( Ursus arctos ) population vital rates and trend for the Northern Continental Divide Ecosystem (NCDE), Montana, between 2004 and 2009 by following radio-collared females and observing their fate and reproductive performance. Our estimates of dependent cub and yearling survival were 0.612 (95% CI = 0.300–0.818) and 0.682 (95% CI = 0.258–0.898). Our estimates of subadult and adult female survival were 0.852 (95% CI = 0.628–0.951) and 0.952 (95% CI = 0.892–0.980). From visual observations, we estimated a mean litter size of 2.00 cubs/litter. Accounting for cub mortality prior to the first observations of litters in spring, our adjusted mean litter size was 2.27 cubs/litter. We estimated the probabilities of females transitioning from one reproductive state to another between years. Using the stable state probability of 0.322 (95% CI = 0.262–0.382) for females with cub litters, our adjusted fecundity estimate ( m x ) was 0.367 (95% CI = 0.273–0.461). Using our derived rates, we estimated that the population grew at a mean annual rate of approximately 3% (λ = 1.0306, 95% CI = 0.928–1.102), and 71.5% of 10,000 Monte Carlo simulations produced estimates of λ > 1.0. Our results indicate an increasing population trend of grizzly bears in the NCDE. Coupled with concurrent studies of population size, we estimate that over 1,000 grizzly bears reside in and adjacent to this recovery area. We suggest that monitoring of population trend and other vital rates using radioed females be continued.

Montana↗
USGS2011

Modifications of traps to reduce bycatch of freshwater turtles

Mortality of freshwater turtles varies among types and deployments of traps. There are few or no losses in hoop or fyke traps set where turtles may reach air, including placement in shallows, addition of floats on traps, and tying traps securely to a stake or to shore. Turtle mortality occurs when traps are set deep, traps are checked at intervals >1 day, and when turtles are captured as bycatch. Devices are available that exclude turtles from traps set for crab or game fish harvest. Slotted gates in front of the trap mouth reduce turtle entry, but small individuals still may be trapped. Incidental take of turtles is preventable by integrating several designs into aquatic traps, such as adding floats to the top of traps so turtles may reach air or an extension tube (chimney, ramp) that creates an escape route.

Journal of Wildlife Management↗
USGS2012

Effects of low-density feeding on elk–fetus contact rates on Wyoming feedgrounds

High seroprevalance for Brucella abortus among elk on Wyoming feedgrounds suggests that supplemental feeding may influence parasite transmission and disease dynamics by altering the rate at which elk contact infectious materials in their environment. We used proximity loggers and video cameras to estimate rates of elk-to-fetus contact (the primary source of brucellosis transmission) during winter supplemental feeding. We compared contact rates during high-density and low-density (LD) feeding treatments that provided the same total amount of food distributed over different areas. Low-density feeding led to >70% reductions in total number of contacts and number of individuals contacting a fetus. Proximity loggers and video cameras provided similar estimates of elk–fetus contact rates. Elk contacted fetuses and random control points equally, suggesting that elk were not attracted to fetuses but encountered them incidentally while feeding. The modeled relationship between contact rate and disease prevalence is nonlinear and LD feeding may result in large reductions in brucellosis prevalence, but this depends on the amount of transmission that occurs on and off feedgrounds.

Journal of Wildlife Management↗
USGS2012

Interseasonal movements of greater sage-grouse, migratory behavior, and an assessment of the core regions concept in Wyoming

Animals can require different habitat types throughout their annual cycles. When considering habitat prioritization, we need to explicitly consider habitat requirements throughout the annual cycle, particularly for species of conservation concern. Understanding annual habitat requirements begins with quantifying how far individuals move across landscapes between key life stages to access required habitats. We quantified individual interseasonal movements for greater sage-grouse (Centrocercus urophasianus; hereafter sage-grouse) using radio-telemetry spanning the majority of the species distribution in Wyoming. Sage-grouse are currently a candidate for listing under the United States Endangered Species Act and Wyoming is predicted to remain a stronghold for the species. Sage-grouse use distinct seasonal habitats throughout their annual cycle for breeding, brood rearing, and wintering. Average movement distances in Wyoming from nest sites to summer-late brood-rearing locations were 8.1 km (SE = 0.3 km; n = 828 individuals) and the average subsequent distances moved from summer sites to winter locations were 17.3 km (SE = 0.5 km; n = 607 individuals). Average nest-to-winter movements were 14.4 km (SE = 0.6 km; n = 434 individuals). We documented remarkable variation in the extent of movement distances both within and among sites across Wyoming, with some individuals remaining year-round in the same vicinity and others moving over 50 km between life stages. Our results suggest defining any of our populations as migratory or non-migratory is innappropriate as individual strategies vary widely. We compared movement distances of birds marked using Global Positioning System (GPS) and very high frequency (VHF) radio marking techniques and found no evidence that the heavier GPS radios limited movement. Furthermore, we examined the capacity of the sage-grouse core regions concept to capture seasonal locations. As expected, we found the core regions approach, which was developed based on lek data, was generally better at capturing the nesting locations than summer or winter locations. However, across Wyoming the sage-grouse breeding core regions still contained a relatively high percentage of summer and winter locations and seem to be a reasonable surrogate for non-breeding habitat when no other information exists. We suggest that conservation efforts for greater sage-grouse implicitly incorporate seasonal habitat needs because of high variation in the amount of overlap among breeding core regions and non-breeding habitat.

Wyoming↗
USGS2012

Spring snow goose hunting influences body composition of waterfowl staging in Nebraska

A spring hunt was instituted in North America to reduce abundance of snow geese ( Chen caerulescens ) by increasing mortality of adults directly, yet disturbance from hunting activities can indirectly influence body condition and ultimately, reproductive success. We estimated effects of hunting disturbance by comparing body composition of snow geese and non-target species, greater white-fronted geese ( Anser albifrons ) and northern pintails ( Anas acuta ) collected in portions of south-central Nebraska that were open (eastern Rainwater Basin, ERB) and closed (western Rainwater Basin, WRB; and central Platte River Valley, CPRV) to snow goose hunting during springs 1998 and 1999. Lipid content of 170 snow geese was 25% (57 g) less in areas open to hunting compared to areas closed during hunting season but similar in all areas after hunting was concluded in the ERB. Protein content of snow geese was 3% (14 g) less in the region open to hunting. Greater white-fronted geese had 24% (76 g; n = 129) less lipids in the hunted portion of the study area during hunting season, and this difference persisted after conclusion of hunting season. We found little difference in lipid or protein content of northern pintails in relation to spring hunting. Indirect effects of spring hunting may be considered a collateral benefit regarding efforts to reduce overabundant snow goose populations. Disrupted nutrient storage observed in greater white-fronted geese represents an unintended consequence of spring hunting that has potential to adversely affect reproduction for this and other species of waterbirds staging in the region.

Nebraska↗
USGS2012

Using persuasive messages to encourage hunters to support regulation of lead shot

Lead shot from hunting adds the toxic metal to environments worldwide. The United States banned lead shot for hunting waterfowl in 1991 and 26 states have lead shot restrictions beyond those mandated for waterfowl hunting. The Minnesota Department of Natural Resources (MDNR) was interested in studying hunter attitudes about expanded restrictions on the use of lead shot for hunting small game to understand what communication strategies might increase public support for potential restrictions on lead shot. We mailed messages about lead shot, including 1,200 control messages and 400 of each of 9 treatment messages, and surveys to 4,800 resident small game hunters. We compared attitudes and intentions related to a possible ban among control and treatment groups. Compared to the control message, all treatment messages elicited more positive attitudes and intentions to support a ban. A basic factual message, messages with references to Ducks Unlimited, and a first-person narrative message generated the strongest support for a ban. Results also demonstrated a substantial relationship between the use of lead shot and response to persuasive messages supporting a ban.

Journal of Wildlife Management↗
USGS2013

A comment on "Novel scavenger removal trials increase wind turbine-caused avian fatality estimates"

In a recent paper, Smallwood et al. (2010) conducted a study to compare their “novel” approach to conducting carcass removal trials with what they term the “conventional” approach and to evaluate the effects of the different methods on estimated avian fatality at a wind power facility in California. A quick glance at Table 3 that succinctly summarizes their results and provides estimated fatality rates and 80% confidence intervals calculated using the 2 methods reveals a surprising result. The confidence intervals of all of their estimates and most of the conventional estimates extend below 0. These results imply that wind turbines may have the capacity to create live birds. But a more likely interpretation is that a serious error occurred in the calculation of either the average fatality rate or its standard error or both. Further evaluation of their methods reveals that the scientific basis for concluding that “many estimates of scavenger removal rates prior to [their] study were likely biased low due to scavenger swamping” and “previously reported estimates of avian fatality rates … should be adjusted upwards” was not evident in their analysis and results. Their comparison to conventional approaches was not applicable, their statistical models were questionable, and the conclusions they drew were unsupported.

Journal of Wildlife Management↗
USGS2013

Power to detect trends in abundance of secretive marsh birds: effects of species traits and sampling effort

Standardized protocols for surveying secretive marsh birds have been implemented across North America, but the efficacy of surveys to detect population trends has not been evaluated. We used survey data collected from populations of marsh birds across North America and simulations to explore how characteristics of bird populations (proportion of survey stations occupied, abundance at occupied stations, and detection probability) and aspects of sampling effort (numbers of survey routes, stations/route, and surveys/station/year) affect statistical power to detect trends in abundance of marsh bird populations. In general, the proportion of survey stations along a route occupied by a species had a greater relative effect on power to detect trends than did the number of birds detected per survey at occupied stations. Uncertainty introduced by imperfect detection during surveys reduced power to detect trends considerably, but across the range of detection probabilities for most species of marsh birds, variation in detection probability had only a minor influence on power. For species that occupy a relatively high proportion of survey stations (0.20), have relatively high abundances at occupied stations (2.0 birds/station), and have high detection probability (0.50), ≥40 routes with 10 survey stations per route surveyed 3 times per year would provide an 80% chance of detecting a 3% annual decrease in abundance after 20 years of surveys. Under the same assumptions but for species that are less common, ≥100 routes would be needed to achieve the same power. Our results can help inform the design of programs to monitor trends in abundance of marsh bird populations, especially with regards to the amount of sampling effort necessary to meet programmatic goals.

Journal of Wildlife Management↗
USGS2013

Pregnancy rates in central Yellowstone bison

Plains bison ( Bison b. bison ) centered on Yellowstone National Park are chronically infected with brucellosis ( Brucella abortus ) and culled along the park boundaries to reduce the probability of disease transmission to domestic livestock. We evaluated the relationship between pregnancy rates and age, dressed carcass weight, and serological status for brucellosis among bison culled from the central Yellowstone subpopulation during the winters of 1996&ndash;1997, 2001&ndash;2002, and 2002&ndash;2003. A model with only dressed carcass weight was the best predictor of pregnancy status for all ages with the odds of pregnancy increasing by 1.03 (95% CI&thinsp;=&thinsp;1.02&ndash;1.04) for every 1-kg increase in weight. We found no effect of age or the serological status for brucellosis on pregnancy rates across age classes; however, we did find a positive association between age and pregnancy rates for bison &ge;2 years old. Bison &ge;2 years old had an overall pregnancy rate of 65% with markedly different rates in alternate ages for animals between 3 and 7 years old. Pregnancy rates were 0.50 (95% CI&thinsp;=&thinsp;0.31&ndash;0.69) for brucellosis positive and 0.57 (95% CI&thinsp;=&thinsp;0.34&ndash;0.78) for brucellosis negative 2- and 3-year-olds and 0.74 (95% CI&thinsp;=&thinsp;0.60&ndash;0.85) in brucellosis positive and 0.69 (95% CI&thinsp;=&thinsp;0.49&ndash;0.85) in brucellosis negative bison &ge;4 years old. Only 1 of 21 bison <2 years old was pregnant. Our findings are important to accurately predict the effects of brucellosis on Yellowstone bison population dynamics. We review our results relative to other studies of Yellowstone bison that concluded serological status for brucellosis influences pregnancy rates.

Wyoming↗
USGS2013

Estimating raptor nesting success: old and new approaches

Studies of nesting success can be valuable in assessing the status of raptor populations, but differing monitoring protocols can present unique challenges when comparing populations of different species across time or geographic areas. We used large datasets from long-term studies of 3 raptor species to compare estimates of apparent nest success (ANS, the ratio of successful to total number of nesting attempts), Mayfield nesting success, and the logistic-exposure model of nest survival. Golden eagles (Aquila chrysaetos), prairie falcons (Falco mexicanus), and American kestrels (F. sparverius) differ in their breeding biology and the methods often used to monitor their reproduction. Mayfield and logistic-exposure models generated similar estimates of nesting success with similar levels of precision. Apparent nest success overestimated nesting success and was particularly sensitive to inclusion of nesting attempts discovered late in the nesting season. Thus, the ANS estimator is inappropriate when exact point estimates are required, especially when most raptor pairs cannot be located before or soon after laying eggs. However, ANS may be sufficient to assess long-term trends of species in which nesting attempts are highly detectable.

Journal of Wildlife Management↗
USGS2013

Demographic variation, reintroduction, and persistence of an island duck ( Anas laysanensis )

Population variation in life history can be important for predicting successful establishment and persistence of reintroduced populations of endangered species. The Laysan duck (Anas laysanensis) is an endangered bird native to the Hawaiian Archipelago that was extirpated from most islands after the introduction of mammalian predators. Laysan ducks were restricted to a single remote island, Laysan Island (4.1 km 2 ), for nearly 150 years. Since the species is not known to disperse between distant Hawaiian Islands today, 42 wild birds from Laysan Island were translocated to another mammalian predator-free low-lying atoll (Midway Atoll; 6.0 km 2 ) to reduce extinction risk. We explored how variation in demography influences establishment and longer-term retention of genetic diversity (rare alleles) for reintroductions of this species. We observed dramatic differences in population growth between the source (λ = 1.18) and reintroduced (λ = 3.28) population. The number of eggs hatched at Midway Atoll was greater than at Laysan Island, however, we found no difference in hatching success (proportion of clutch hatched) between populations. Adult females produced 3 times as many fledglings per breeding year on Midway Atoll compared to Laysan Island. We estimated population abundance of both populations until 2010 and applied a Gompertz model with a Bayesian approach to infer density dependence, process variation, observation error, and carrying capacity for the Laysan Island and Midway Atoll populations. The carrying capacity from the Gompertz model for Midway Atoll (K = 883 ± 210 SD) was estimated to be greater than that of Laysan Island (K = 598 ± 76 SD). Translocations with small numbers of founders and no immigration can create population bottlenecks, leading to loss of genetic variation over time, and potentially reducing the reintroduced population's viability or its potential to serve as a source for future translocations. Therefore, we also assessed the probability of retaining rare alleles in an isolated reintroduced Laysan duck population using life history parameters observed from the Laysan Island and Midway Atoll populations; we concluded that additional founders are needed under scenarios using demographic estimates from both Laysan Island and Midway Atoll to retain either 90% or 95% of source population genetic diversity.

Laysan Island;Midway Atoll↗