Postcatastrophe Population Dynamics and Density Dependence of an Endemic Island Duck

ABSTRACT Laysan ducks (Anas laysanensis) are restricted to approximately 9 km² in the Northwestern Hawaiian Islands, USA. To evaluate the importance of density dependence for Laysan ducks, we conducted a Bayesian analysis to estimate the parameters of a Gompertz model and the magnitude of process variation and observation error based on the fluctuations in Laysan duck abundance on Laysan Island from 1994 to 2007. This model described a stationary distribution for the population at carrying capacity that fluctuates around a long-term mean of 456 ducks and is between 316 to 636 ducks 95% of the time. This range of expected variability can be used to identify changes in population size that warn of catastrophic events. Density-dependent population dynamics may explain the recovery of Laysan duck from catastrophic declines and allow managers to identify population monitoring thresholds.     

Mortality in Laysan ducks (Anas laysanensis) by emaciation complicated by Echinuria uncinata on Laysan Island, Hawaii, 1993

In November 1993, unusual mortality occurred among endangered Laysan ducks on Laysan Island, one of the remote refugia of the Northwestern Hawaiian Islands National Wildlife Refuge (USA). Ten live ducks were emaciated, and blood samples documented anemia, heterophilia, and eosinophilia. Pathology in 13 duck carcasses revealed emaciation, marked thickening of the proventricular wall, abundant mucus, and nodules in the gastrointestinal tract. Histology revealed granulomata associated with nematodes in the proventriculus, small intestines, and body walls of nine of 10 ducks examined on histology. We suspect that low rainfall and low food abundance that year contributed to enhanced pathogenicity of parasite infection, either through increased exposure or decreased host resistance. Because the Laysan duck is found only on Laysan island and is critically endangered, translocation of this species to other islands is being considered. Given that we have not seen pathology associated with Echinuria spp. in native waterfowl on other Hawaiian Islands and given the parasite's potential to cause significant lesions in Laysan ducks, it will be important to prevent the translocation of Echinuria spp.     

Survival of Wood Duck Ducklings and Broods in Mississippi and Alabama

ABSTRACT Although North American wood ducks (Aix sponsa) are well-studied throughout their range, researchers know little about demographic and environmental factors influencing survival of ducklings and broods, which is necessary information for population management. We studied radiomarked female and duckling wood ducks that used nest boxes and palustrine wetlands at Noxubee National Wildlife Refuge (NNWR) in Mississippi, USA, in 1996–1999, and riverine wetlands of the Tennessee-Tombigbee Rivers and Waterway (TTRW) system in Alabama in 1998–1999. We estimated survival of ducklings and broods and evaluated potentially important predictors of duckling survival, including age and body mass of brood-rearing females, hatch date of ducklings, duckling mass, brood size at nest departure, inter-day travel distance by ducklings, site and habitat use, and daily minimum air temperature and precipitation. At NNWR, survival of 300 radiomarked ducklings ranged from 0.15 (95% CI = 0.04-0.27) to 0.24 (95% CI = 0.13-0.38) and was 0.21 (95% CI = 0.15-0.28) for 1996–1999. Our overall estimate of brood survival was 0.64 (n = 91; 95% CI = 0.54-0.73). At TTRW, survival of 129 radiomarked ducklings was 0.29 in 1998 (95% CI = 0.20-0.41) and 1999 (95% CI = 0.13-0.45) and was 0.29 (95% CI = 0.20-0.40) for 1998–1999. Our overall estimate of brood survival was 0.71 (n = 38; 95% CI = 0.56-0.85). At NNWR, models that included all predictor variables best explained variation in duckling survival. Akaike weight (w_i) for the best model was 0.81, suggesting it was superior to other models (<0.01 < w_i < 0.18). We detected 4 competing models for duckling survival at TTRW. Inter-day distance traveled by ducklings was important as this variable appeared in all 4 models; duckling survival was positively related to this variable. Patterns of habitat-related survival were similar at both study areas. Ducklings in broods that used scrub-shrub habitats disjunct from wetlands containing aggregations of nest boxes had greater survival probabilities than birds remaining in wetlands with such nest structures. Managers may increase local wood duck recruitment by promoting availability of suitable brood habitats (e.g., scrub-shrub wetlands) without aggregations of nest boxes that may attract predators and by dispersing nest boxes amid or adjacent to these habitats. We did not determine an optimal density of nest boxes relative to local or regional population goals, which remains important research and conservation needs.     

Food Resources for Wintering and Spring Staging Black Ducks

Abstract: A bioenergetic approach has been adopted as a planning tool to set habitat management objectives by several United States Fish and Wildlife Service North American Waterfowl Management Plan Joint Ventures. A bioenergetics model can be simplified into 2 major components, energetic demand and energetic supply. Our goal was to estimate habitat-specific food availability, information necessary for estimating energy supply for black ducks (Anas rubripes) wintering on Long Island, New York, USA. We collected both nektonic and benthic samples from 85 wetland sites dispersed among 5 habitat types (salt marsh, mud flat, submersed aquatic vegetation, brackish bay, and freshwater) commonly used by black ducks in proportion to expected use. Biomass varied among habitats (F_4,5 > 7.46, P < 0.03) in 2004–2005, but there was only marginal variation in 2005–2006 (F_3,4 = 5.75, P = 0.06). Mud flats had the greatest biomass (1,204 kg/ha, SE = 532), followed by submersed aquatic vegetation (61 kg/ha, SE = 18), and salt marsh (34 kg/ha, SE = 6). In the second year of the study, freshwater had the greatest biomass (306 kg/ha, SE = 286), followed by mud flats (85 kg/ha, SE = 63), and salt marsh (35 kg/ha, SE = 4). Our results suggest food density on wintering grounds of black ducks on coastal Long Island is considerably lower than for dabbling ducks using inland freshwater habitats, indicating black duck populations are more likely than other species of dabbling ducks to be limited by winter habitat. We recommend targeting preservation, restoration, and enhancement efforts on salt marsh habitat.     

Microsatellite markers for two stifftail ducks: the white‐headed duck,Oxyura leucocephala,and the ruddy duck,O. jamaicensis

Hybridization with a close relative, the North American ruddy duck (Oxyura jamaicensis), is a major problem for the conservation of the endangered white‐headed duck (Oxyura leucocephala). We report the development of 11 microsatellite markers that can facilitate the identification of hybrids as well as the study of the population structure of both species across their distributions. These markers were tested in 63 white‐headed ducks and 50 ruddy ducks and show a larger diversity in the latter species.     

Geographic variation in the Laysan Finch (Telespyza cantans)

Summary Significant differences in bill shape exist between the endemic Laysan population and introduced populations of the Laysan Finch (Drepanidinae:Telespyza cantans) at Pearl and Hermes Reef. Furthermore, there are significant differences in bill shape between two of four finch populations on the islands of Pearl and Hermes Reef. The variation in finch bill shape is paralleled by geographic variation in the large, hard mericarps ofTribulus cistoides, an important food item at Pearl and Hermes Reef. There are three possible explanations for the observed variation. Environmental influence may be a non-evolutionary cause of the variation, or genetic drift and natural selection may have caused the differences in morphology. Preliminary results suggest that both genetic drift and natural selection have been acting on the populations. Continuing studies, including investigation of genetic variation and cross-fostering experiments to determine heritability of morphological traits and effects of environment on morphological traits, are planned to test the various hypotheses.     

Genetic admixture supports an ancient hybrid origin of the endangered Hawaiian duck

Speciation is regarded primarily as a bifurcation from an ancestral species into two distinct taxonomic units, but gene flow can create complex signals of phylogenetic relationships, especially among different loci. We evaluated several hypotheses that could account for phylogenetic discord between mitochondrial DNA (mtDNA) and nuclear DNA (nuDNA) within Hawaiian duck (Anas wyvilliana), including stochastic lineage sorting, mtDNA capture and widespread genomic introgression. Our results best support the hypothesis that the contemporary Hawaiian duck is descended from an ancient hybridization event between the mallard (Anas platyrhynchos) and Laysan duck (Anas laysanensis). Whereas mtDNA clearly shows a sister relationship between Hawaiian duck and mallard, nuDNA is consistent with a genetic mosaic with nearly equal contributions from Laysan duck and mallard. In addition, coalescent analyses suggest that gene flow from either mallard or Laysan duck, depending on the predefined tree topology, is necessary to explain contemporary genetic diversity in Hawaiian ducks, and these estimates are more consistent with ancient, rather than contemporary, hybridization. Time since divergence estimates suggest that the genetic admixture event occurred around the Pleistocene–Holocene boundary, which is further supported by circumstantial evidence from the Hawaiian subfossil record. Although the extent of reproductive isolation from either putative parental taxon is not currently known, these species are phenotypically, genetically and ecologically different, and they meet primary criteria used in avian taxonomy for species designation. Thus, the available data are consistent with an admixed origin and support the hypothesis that the Hawaiian duck may represent a young hybrid species.     

Winter Survival of Female Ring-Necked Ducks in the Southern Atlantic Flyway

North American waterfowl harvest regulations are largely guided by the status of breeding populations. Nonetheless, understanding the demographics of wintering waterfowl populations can elucidate the effects of hunting pressure on population dynamics. The ring-necked duck (Aythya collaris) breeds and winters in all North American administrative flyways and is one of the most abundant and most harvested diving ducks in the Atlantic Flyway. But few studies have investigated the winter ecology of ring-necked ducks. We used a known-fate analysis to estimate period survival probability using data from 87 female ring-necked ducks marked with satellite transmitters in 2 regions of the southern Atlantic Flyway during winters of 2017–2018 and 2018–2019. Winter (128-day) survival probability was higher for individuals in the Red Hills region of southern Georgia and northern Florida (0.875, 95% CI = 0.691–0.952) than individuals in central South Carolina (0.288, 95% CI = 0.082–0.514). We attribute the regional disparity in winter survival probabilities to differences in hunting pressure, which are reflected in the number of harvests we observed in each region. Our findings warrant further investigation into regional variation in winter survival of southern Atlantic Flyway ring-necked ducks, and, specifically, the relationship between variable harvest pressure and winter survival and its influence on ring-necked duck population dynamics and adaptive harvest management decisions. © 2020 The Wildlife Society.     

Lessons from the Tōhoku tsunami: A model for island avifauna conservation prioritization

Earthquake‐generated tsunamis threaten coastal areas and low‐lying islands with sudden flooding. Although human hazards and infrastructure damage have been well documented for tsunamis in recent decades, the effects on wildlife communities rarely have been quantified. We describe a tsunami that hit the world's largest remaining tropical seabird rookery and estimate the effects of sudden flooding on 23 bird species nesting on Pacific islands more than 3,800 km from the epicenter. We used global positioning systems, tide gauge data, and satellite imagery to quantify characteristics of the Tōhoku earthquake‐generated tsunami (11 March 2011) and its inundation extent across four Hawaiian Islands. We estimated short‐term effects of sudden flooding to bird communities using spatially explicit data from Midway Atoll and Laysan Island, Hawai'i. We describe variation in species vulnerability based on breeding phenology, nesting habitat, and life history traits. The tsunami inundated 21%–100% of each island's area at Midway Atoll and Laysan Island. Procellariformes (albatrosses and petrels) chick and egg losses exceeded 258,500 at Midway Atoll while albatross chick losses at Laysan Island exceeded 21,400. The tsunami struck at night and during the peak of nesting for 14 colonial seabird species. Strongly philopatric Procellariformes were vulnerable to the tsunami. Nonmigratory, endemic, endangered Laysan Teal (Anas laysanensis) were sensitive to ecosystem effects such as habitat changes and carcass‐initiated epizootics of avian botulism, and its populations declined approximately 40% on both atolls post‐tsunami. Catastrophic flooding of Pacific islands occurs periodically not only from tsunamis, but also from storm surge and rainfall; with sea‐level rise, the frequency of sudden flooding events will likely increase. As invasive predators occupy habitat on higher elevation Hawaiian Islands and globally important avian populations are concentrated on low‐lying islands, additional conservation strategies may be warranted to increase resilience of island biodiversity encountering tsunamis and rising sea levels.     

Breeding Ecology of Mottled Ducks: A Review

Mottled ducks (Anas fulvigula) are endemic to the Gulf Coast of North America, and their range stretches from Alabama to the Laguna Madre of Mexico, with a distinct population in peninsular Florida and an introduced population in South Carolina. As one of the few non-migratory ducks in North America, mottled ducks depend on a variety of locally available habitat throughout the annual cycle, and threats to these landscapes may affect mottled ducks more acutely than migratory species. Annual population monitoring has revealed declines in mottled duck populations in Texas and Louisiana since 2008, and the genetic integrity of the Florida population has been muddled by the presence of large numbers of feral mallards (Anas platyrhynchos) resulting in hybridization. Similar to other closely related dabbling ducks, mottled duck populations are influenced by recruitment and breeding season survival, so changes in these factors may contribute to population decline. Accordingly, researchers have attempted to address various aspects of mottled duck breeding season ecology and population dynamics since the 1950s. We conducted a literature review on this topic by searching a combination of key terms using Google Scholar, including mottled duck, nesting ecology, habitat use, breeding incidence, nest success, brood, and breeding season survival, and followed citation trees to eventually aggregate information from nearly 50 publications on mottled duck breeding ecology. Our review concluded that mottled ducks use brackish and intermediate coastal marsh, including managed impoundments, and agricultural land during the breeding season. Their nests can be found in pastures, levees, dry cordgrass marsh, cutgrass marsh, spoil banks, and small islands. Nesting propensity and nest success estimates are often lower than other waterfowl species that are characterized by stable or increasing populations. Broods use wetlands composed of a mix of open water with submerged and emergent vegetation. Breeding season survival is higher for the Florida population than the western Gulf Coast population, but adult survival in both geographies is comparable to (or higher than) that of other dabbling duck species. Breeding habitat use, breeding season survival, and nest-site selection and success have been studied extensively in mottled ducks, whereas information on nesting propensity, renesting intensity, and post-hatch ecology is lacking. © 2021 The Wildlife Society.     

Differential Effects of an Intense Wildfire on Survival of Sympatric Snakes

Abstract: We analyzed 16 years of mark-recapture data to investigate whether a wildfire influenced survival of an arboreal ambush-forager (broad-headed snake [Hoplocephalus bungaroides]) and a terrestrial active forager (small-eyed snake Cryptophis nigrescens). We predicted that wildfire would cause direct mortality and reduce subsequent survival of both snake species. Contrary to this prediction, wildfire did not affect abundance of broad-headed snakes, but abundance of small-eyed snakes decreased by 48% after the wildfire. Estimated annual survival of small-eyed snakes was 37% lower after fire (s=0.47, SE=0.07) than before fire (s=0.74, SE=0.05). Prescribed burning may be a suitable tool for creating open habitat mosaics for the endangered broad-headed snake.     

Pintail and Mallard Survival in California Relative to Habitat,Abundance, and Hunting

ABSTRACT The influence of habitat, waterfowl abundance, and hunting on winter survival of waterfowl is not well understood. We studied late August-March survival of 163 after-hatch-year (AHY) and 128 hatch-year (HY) female mallards (Anas platyrhynchos) radiotagged in Sacramento Valley (SACV) and 885 AHY female northern pintails (A. acuta) radiotagged throughout the Central Valley of California, USA, relative to flooded habitat (HAB), January abundance of each species (JMAL or JPIN), hunter-days (HDY), and a hunting pressure index (HPI) that combined these variables. From EARLY (1987–1994) to LATE (1998–2000), HAB increased 39%, JPIN increased 45%, JMAL increased 53%, HDY increased 21%, duck-hunting season increased from 59 days to 100 days, and the female daily bag limit doubled to 2 for mallards but remained 1 for pintails. Survival (± SE) was greater during LATE versus EARLY for pintails radiotagged in each region (SACV: 93.2 ± 2.1% vs. 87.6 ± 3.0%; Suisun Marsh: 86.6 ± 3.2% vs. 77.0 ± 3.7%; San Joaquin Valley: 86.6 ± 3.1% vs. 76.9 ± 4.1%) but not for SACV mallards (AHY: 70.6 ± 7.2% to 74.4 ± 7.7% vs. 80.1 ± 7.2% to 82.8 ± 5.6%; HY: 48.7 ± 9.1% [1999–2000 only] vs. 63.5 ± 8.8% to 67.6 ± 8.0%). Most pintail (72%) and mallard (91%) deaths were from hunting, and lower HPI and higher JPIN or JMAL were associated with reduced mortality. Increased HAB was associated with reduced winter mortality for pintails but not for SACV mallards. Pintail survival rates that we measured were within the range reported for other North American wintering areas, and during LATE were higher than most, even though our study duration was 68–110 days longer. Winter survival rates of SACV mallards were also within the reported range. However, with higher bag limits and longer seasons, mallard survival during LATE was lower than in most other wintering areas, especially during 1999–2000, when high winds on opening weekend resulted in high hunting mortality. Habitat conservation and favorable agriculture practices helped create a Central Valley wintering environment where natural mortality of mallards and pintails was low and survival varied with hunting mortality. We recommend regulations and habitat management that continue to minimize natural mortality while allowing sustainable harvest at a level that helps maintain strong incentive for management of Central Valley waterfowl habitats, including the large portion that is privately owned.     

Relative Importance of Vital Rates to Population Dynamics of Wood Ducks

The wood duck (Aix sponsa) is a common and important cavity-nesting duck in North America; however, we know very little about how changes in vital rates influence population growth rate (λ). We used estimates of fertility and survival of female wood ducks from our nest-box studies in South Carolina, Alabama, and Georgia, USA, to create a stage-based matrix population model. We conducted perturbation analyses and ranked elasticity values to examine the relative importance of 17 component vital rates to λ. Female survival is influenced by nest success, so we recognized this female heterogeneity in our analyses. Four vital rates showed the greatest importance to λ. Analytic elasticities were greatest for breeding season and nonbreeding season survival of females that nested successfully, followed by nest success and female recruitment to the breeding population. Differences in female quality were important to λ. Next, we used process variation of vital rates and conducted life-stage simulation analyses (LSA) followed by variance decomposition to determine the amount of variation in λ explained by each vital rate. Female recruitment to the breeding population explained 57.7% of the variation in λ followed by nest success (11.4%), and breeding and nonbreeding season survival of females that nested successfully (9.3% and 9.4%, respectively). Together these 4 vital rates explained 88% of the variation in λ. Mean asymptotic population growth rate (λ = 0.80 ± 0.08 [SD]) from LSA revealed a declining population. Recruitment of females hatched from nest boxes was insufficient to sustain the nest-box population. However, including yearling (SY) females that were produced outside of nest boxes (i.e., immigrants) increased recruitment rates 1.5 to 2 times more than when only SY females recruited from nest boxes were included. Future research that examines how emigration and immigration interact with survival and reproduction to influence local population dynamics of wood ducks will be important for identifying the value of nest-box programs to wood duck conservation and management. © 2019 The Wildlife Society.     

A Double-Observer Method to Estimate Detection Rate During Aerial Waterfowl Surveys

Abstract We evaluated double-observer methods for aerial surveys as a means to adjust counts of waterfowl for incomplete detection. We conducted our study in eastern Canada and the northeast United States utilizing 3 aerial-survey crews flying 3 different types of fixed-wing aircraft. We reconciled counts of front- and rear-seat observers immediately following an observation by the rear-seat observer (i.e., on-the-fly reconciliation). We evaluated 6 a priori models containing a combination of several factors thought to influence detection probability including observer, seat position, aircraft type, and group size. We analyzed data for American black ducks (Anas rubripes) and mallards (A. platyrhynchos), which are among the most abundant duck species in this region. The best-supported model for both black ducks and mallards included observer effects. Sample sizes of black ducks were sufficient to estimate observer-specific detection rates for each crew. Estimated detection rates for black ducks were 0.62 (SE = 0.10), 0.63 (SE = 0.06), and 0.74 (SE = 0.07) for pilot-observers, 0.61 (SE = 0.08), 0.62 (SE = 0.06), and 0.81 (SE = 0.07) for other front-seat observers, and 0.43 (SE = 0.05), 0.58 (SE = 0.06), and 0.73 (SE = 0.04) for rear-seat observers. For mallards, sample sizes were adequate to generate stable maximum-likelihood estimates of observer-specific detection rates for only one aerial crew. Estimated observer-specific detection rates for that crew were 0.84 (SE = 0.04) for the pilot-observer, 0.74 (SE = 0.05) for the other front-seat observer, and 0.47 (SE = 0.03) for the rear-seat observer. Estimated observer detection rates were confounded by the position of the seat occupied by an observer, because observers did not switch seats, and by land-cover because vegetation and landform varied among crew areas. Double-observer methods with on-the-fly reconciliation, although not without challenges, offer one viable option to account for detection bias in aerial waterfowl surveys where birds are distributed at low density in remote areas that are inaccessible by ground crews. Double-observer methods, however, estimate only detection rate of animals that are potentially observable given the survey method applied. Auxiliary data and methods must be considered to estimate overall detection rate.     

Age-Specific Survival and Probable Causes of Mortality in Female Lesser Prairie-Chickens

ABSTRACT Long-term population declines and habitat reductions have increased concern over the status of the lesser prairie-chicken (Tympanuchus pallidicinctus). Robust estimates of demographic parameters are essential for identifying population declines and planning effective management. We evaluated the effects of age and season on the survival of female lesser prairie-chickens at 2 sites in southwestern Kansas, USA. Using telemetry data from a 7-year field study (from 1997 to 2003), we estimated seasonal (Apr—Sep) and annual (Apr—Mar) survival. We also examined daily survival rates of females attending nests during the 26-day incubation period and young during the 14-day early brood-rearing period. We evaluated the probable mortality causes of radiomarked birds by examining evidence at recovery sites. We captured 227 female lesser prairie-chickens (87 yearlings, 117 ad, and 23 age undetermined) and fitted them with radiotransmitters. Estimates of 12-month survival were lower among yearlings (Ŝ₁₂ = 0.429, SE = 0.117) and adults at site I (Ŝ₁₂ > = 0.302, SE = 0.080) than among yearlings (Ŝ₁₂ = 0.588, SE = 0.100) and adults at site II (Ŝ₁₂ > = 0.438, SE = 0.083). The patterns in timing of mortality and age-specific 6-month survival were consistent with those of 12-month estimates at site I from 1998 to 2002, with a peak in mortality during May and June. Females tending to nests or to prefledged chicks had lower daily survival (DŜR_tend = 0.993, SE = 0.001) than females not involved in these activities (DŜR_{failedbreeder} = 0.997, SE = 0.002). We recorded 92 mortalities from April 1997 to March 2003, and 59% and 11% were attributed to predation by mammals and raptors, respectively. Our research suggests that predation during the nesting season can have a major impact on lesser prairie-chicken demography, and conservation efforts should focus on enhancing female survival during the nesting and brood-rearing seasons.     

Occupancy Patterns of Breeding American Black Ducks

Occupancy patterns can assist with the determination of habitat limitation during breeding or wintering periods and can help guide population and habitat management efforts. American black ducks (Anas rubripes; black ducks) are thought to be limited by habitat and food availability during the winter, but breeding sites may also limit the size or growth potential of the population. The Canadian Wildlife Service conducts an annual breeding waterfowl survey that we used to explore the hypothesis that black duck carrying capacity is limited by wetlands available for breeding in Québec, Canada. We applied single-visit, multi-species occupancy models to the 1990–2015 population survey data to determine if there was evidence the black duck population was limited by breeding habitat. Using a dynamic (multi-season) occupancy modeling approach, we estimated latent occupancy (occupancy accounting for imperfect detection) of black ducks and then used latent occupancy estimates to derive occupancy, colonization, and extirpation rates. We jointly modeled the occupancy dynamics of black ducks and other duck species in wetlands where both species were present. Throughout the duration of the survey, 44% of wetlands were never observed to be occupied by black ducks. Occupancy models showed wetland size was positively associated with occupancy at the first time step (initial occupancy) and colonization. All 2-species models indicated initial black duck occupancy, persistence (continued occupancy), and colonization were positively associated with the presence of a second species. Colonization rate over the 26-year period ranged from 7% to 27% across all models. Extirpation rates were similar and were constant through time within each model. Low occupancy rates, combined with approximately equal colonization and extirpation rates, suggest there are available wetlands for breeding black ducks in their core breeding area. If breeding habitats are not saturated, this suggests migration or wintering areas may be more limiting to black duck population abundance. © 2019 The Wildlife Society.     

Variation in Breeding Season Survival of Female Harlequin Ducks

ABSTRACT Quantifying sources of variation in demographic rates can provide insight into processes underlying population dynamics and subsequently direct wildlife conservation. In the context of avian life history, understanding patterns of variation in survival rates of breeding females is particularly relevant because this cohort often has a disproportionately large effect on population dynamics. We estimated survival probability for 144 adult female harlequin ducks (Histrionicus histrionicus) that we marked with radiotransmitters and tracked at 4 breeding areas in western North America. Model selection results indicated both regional and temporal variation in survival rates, with most mortality attributed to predation. Cumulative survival probability (±SE) during the 100-day study period was lower at 2 sites in the Rocky Mountains of Alberta, Canada (AB1 and AB2: 0.75 ± 0.11) than in the Coast Mountains of British Columbia, Canada (BC: 0.88 ± 0.08) or the Cascade Mountains of Oregon, USA (OR: 0.89 ± 0.08). Survival also was lower during incubation than nest-initiation or brood-rearing stages at all 4 study areas. In comparison to other annual cycle stages and locations, harlequin duck mortality rates were highest on the breeding grounds, suggesting that management actions designed to reduce mortality during breeding would achieve meaningful population-level benefits.     

Translocation and early post-release demography of endangered Laysan teal

In an attempt to reduce the high extinction risk inherent to small island populations, we translocated wild Laysan teal Anas laysanensis to a portion of its presumed prehistoric range. Most avian translocations lack the strategic post-release monitoring needed to assess early population establishment or failure. Therefore, we monitored the survival and reproduction of all founders, and their first-generation offspring using radio telemetry for 2 years after the first release. Forty-two Laysan teal were sourced directly from the only extant population on Laysan Island and transported 2 days by ship to Midway Atoll. All birds survived the translocation with nutritional and veterinary support, and spent between 4 and 14 days in captivity. Post-release survival of 42 founders was 0.857 (95% CI 0.86–0.99) during 2004–2006 or annualized 0.92 (95% CI 0.83–0.98). Seventeen of 18 founding hens attempted nesting in the first two breeding seasons. Fledgling success was 0.57 (95% CI 0.55–0.60) in 2005 and 0.63 (95% CI 0.62–0.64) in 2006. The effective founding female population ( N _e) was 13. We applied these initial demographic rates to model population growth. The nascent population size increased to >100 after only 2 years post-release ( λ =1.73). If this growth rate continues, the size of the Midway population could surpass the source population before 2010.     

Waterfowl Use of Dense Nesting Cover in the Canadian Parklands

ABSTRACT Dense nesting cover (DNC) has been a conspicuous component of habitat management for upland-nesting ducks for >30 years, but its benefits for nesting ducks have been contentious. During 1994–1999 we monitored 3,058 dabbling duck (Anas spp.) nests in 84 DNC fields located throughout the Canadian Parklands to examine sources of among-field variation in nest density and nesting success. Nest density averaged 1.51 (SE=0.15) nests/ha and overall nesting success was 20.4%, but there was pronounced annual variation in both estimates. Nesting success increased with increasing field size (range = 6–111 ha), but nest density remained constant. Nest density increased with percent wetland habitat within DNC fields and declined with percent perennial cover in the surrounding 2.4 × 2.4-km landscape, but these variables were not important for predicting nesting success. Nest abundance and nesting success roughly doubled in fields seeded with alfalfa (Medicago sativa) or sweet clovers (Melilotus spp.), but there was no benefit from using native as opposed to tame grasses. We recommend that waterfowl managers in the Canadian Parklands establish DNC with alfalfa in large fields in landscapes with abundant wetlands but minimal competing cover.