Courtney L. Amundson

A hierarchical model combining distance sampling and time removal to estimate detection probability during avian point counts

ABSTRACT Imperfect detection during animal surveys biases estimates of abundance and can lead to improper conclusions regarding distribution and population trends. Farnsworth et al. (2005) developed a combined distance-sampling and time-removal model for point-transect surveys that addresses both availability (the probability that an animal is available for detection; e.g., that a bird sings) and perceptibility (the probability that an observer detects an animal, given that it is available for detection). We developed a hierarchical extension of the combined model that provides an integrated analysis framework for a collection of survey points at which both distance from the observer and time of initial detection are recorded. Implemented in a Bayesian framework, this extension facilitates evaluating covariates on abundance and detection probability, incorporating excess zero counts (i.e. zero-inflation), accounting for spatial autocorrelation, and estimating population density. Species-specific characteristics, such as behavioral displays and territorial dispersion, may lead to different patterns of availability and perceptibility, which may, in turn, influence the performance of such hierarchical models. Therefore, we first test our proposed model using simulated data under different scenarios of availability and perceptibility. We then illustrate its performance with empirical point-transect data for a songbird that consistently produces loud, frequent, primarily auditory signals, the Golden-crowned Sparrow (Zonotrichia atricapilla); and for 2 ptarmigan species (Lagopus spp.) that produce more intermittent, subtle, and primarily visual cues. Data were collected by multiple observers along point transects across a broad landscape in southwest Alaska, so we evaluated point-level covariates on perceptibility (observer and habitat), availability (date within season and time of day), and abundance (habitat, elevation, and slope), and included a nested point-within-transect and park-level effect. Our results suggest that this model can provide insight into the detection process during avian surveys and reduce bias in estimates of relative abundance but is best applied to surveys of species with greater availability (e.g., breeding songbirds).

The Role of Predator Removal, Density- Dependence, and Environmental Factors on Mallard Duckling Survival in North Dakota

ABSTRACT Duckling survival is an important component of mallard (Anas platyrhynchos) recruitment and population growth, yet many factors regulating duckling survival are poorly understood. We investigated factors affecting mallard duckling survival in the drift prairie of northeastern North Dakota, 2006–2007. Mammalian meso-predators were removed by trapping on 4 92.3 km2 study sites and another 4 study sites served as controls. We monitored 169 broods using telemetry and periodic resighting, and we modeled cumulative survival to 30 days of age (Ŝ30d) using the nest survival module in Program MARK. Duckling survival was not affected by predator removal (Ŝ30d-Control = 0.208, 85% CI: 0.182–0.234; Ŝ30d-Trapped = 0.183, 85% CI: 0.155–0.211) and was only weakly negatively correlated with duckling density. Duckling survival was higher in 2007 (Ŝ30d-2007 = 0.264, 85% CI: 0.193–0.355) than 2006 (Ŝ30d-2006 = 0.157, 85% CI: 0.084–0.252) and increased with total seasonal and semipermanent wetland area and declined with perennial cover in the surrounding landscape. Broods that hatched earlier in the season (especially in 2006) and ducklings that were heavier at hatch also had higher survival. Our estimates of duckling survival are among the lowest reported for mallards and contradict previous research in Saskatchewan that found predator removal increased duckling survival. However, our results are consistent with other studies suggesting that earlier hatch date, increased wetland availability, and better duckling condition lead to increased survival. Management actions that increase wetland density, improve nest success early in the season, and potentially target brood-specific predators such as mink (Neovison vison) would likely lead to higher duckling survival.

A multiscale assessment of tree avoidance by prairie birds

ABSTRACT In North America, grassland bird abundances have declined, likely as a result of loss and degradation of prairie habitat. Given the expense and limited opportunity to procure new grasslands, managers are increasingly focusing on ways to improve existing habitat for grassland birds, using techniques such as tree removal. To examine the potential for tree removal to benefit grassland birds, we conducted 446 point counts on 35 grassland habitat patches in the highly fragmented landscape of west-central Minnesota during 2009–2011. We modeled density of four grassland bird species in relation to habitat composition at multiple scales, focusing on covariates that described grass, woody vegetation (trees and large shrubs), or combinations of grass and woody vegetation. The best-supported models for all four grassland bird species incorporated variables measured at multiple scales, including local features such as grass height, litter depth, and local tree abundance, as well as landscape-level measures of grass and tree cover. Savannah Sparrows (Passerculus sandwichensis), Sedge Wrens (Cistothorus platensis), and Bobolinks (Dolichonyx oryzivorus) responded consistently and negatively to woody vegetation, but response to litter depth, grass height, and grassland extent were mixed among species. Our results suggest that reducing shrub and tree cover is more likely to increase the density of grassland birds than are attempts to improve grass quality or quantity. In particular, tree removal is more likely to increase density of Savannah Sparrows and Sedge Wrens than any reasonable changes in grass quality or quantity. Yet tree removal may not result in increased abundance of grassland birds if habitat composition is not considered at multiple scales. Managers will need to either manage at large scales (80–300 ha) or focus their efforts on removing trees in landscapes that contain some grasslands but few nearby wooded areas.

Anthelmintics Increase Survival of American Coot (Fulica americana) Chicks

ABSTRACT. Helminthic parasites occur at high frequencies in waterbirds, but little is known about their effects on host population dynamics. In 2004–2005, we examined the effect of helminthic parasites on fledging success of semiprecocial American Coot (Fulica americana) chicks by experimentally dosing day-old chicks with the anthelmintic drug fenbendazole (treatments) or sterile water (controls) and measuring their survival to 40 days of age using mark—resighting analyses. In 2005, we also provided anthelmintic (treatment) or plain (control) supplemental food to incubating adults to determine whether chick survival was further influenced by parasite burdens of parents. Treated offspring had approximately half as many helminthic parasites as untreated offspring, but we could not demonstrate a reduction in parasite burdens among treated adults. Chicks that received fenbendazole in 2004 had 0.510 (85% confidence interval [CI]: 0.447–0.588) cumulative survival to 40 days of age, versus 0.387 (85% CI: 0.305–0.462) survival in untreated chicks. In 2005, offspring survival to 40 days posthatch was an additive function of both offspring and parental treatment, with survival averaging 0.578 (85% CI: 0.502–0.654) when both parents and chicks were treated, 0.461 (85% CI: 0.381–0.544) when only chicks were treated, 0.452 (85% CI: 0.375–0.533) when only adults were treated, and 0.334 (85% CI: 0.254–0.424) when neither was treated with fenbendazole. Our results provide compelling evidence that treatment with anthelmintic drugs increased fledging success and suggest that parasite burdens have important consequences for offspring survival in American Coots.

Use of Nape Tags for Marking Offspring of Precocial Waterbirds

Abstract. Individualized markers that allow organisms to be identified without recapture are invaluable for studies of survival, movement, and behavior. Nape tags consisting of brass safety pins with unique combinations of two or three colored plastic beads were used to mark 5,868 American Coot (Fulica americana) chicks and 331 Ruddy Duck (Oxyura jamaicensis), 157 King Eider (Somateria spectabilis) and 664 White-winged Scoter (Melanitta fusca deglandi) ducklings. These markers allowed for documentation of parent-offspring interactions, post-hatching survival, brood movements and brood-mixing behaviors. Nape tags were inexpensive, easy to make, easy to observe with binoculars or spotting scopes and provided over 100 two-bead or 1,000 three-bead color combinations for individual identification. For coots, there was no evidence of color biases affecting parental care or offspring survival, although some colors (white, yellow) were easier to detect than others (brown). The only observed problem was marker loss, with tag loss rates reaching 20% near fledging age. Nape tags worked effectively on coots and ducklings and may be useful for other precocial waterbirds.

Montane-breeding Bird Distribution and Abundance Across National Parks of Southwestern Alaska

Abstract Between 2004 and 2008, biologists conducted an inventory of breeding birds during May–June primarily in montane areas (>100 m above sea level) of Aniakchak National Monument and Preserve (...

Helminth community structure in two species of arctic-breeding waterfowl.

Climate change is occurring rapidly at high latitudes, and subsequent changes in parasite communities may have implications for hosts including wildlife and humans. Waterfowl, in particular, harbor numerous parasites and may facilitate parasite movement across broad geographic areas due to migratory movements. However, little is known about helminth community structure of waterfowl at northern latitudes. We investigated the helminth communities of two avian herbivores that breed at high latitudes, Pacific black brant (Branta bernicla nigricans), and greater white-fronted geese (Anser albifrons), to examine effects of species, geographic area, age, and sex on helminth species richness, aggregation, prevalence, and intensity. We collected 83 and 58 black brant and white-fronted geese, respectively, from Arctic and Subarctic Alaska July–August 2014. We identified 10 known helminth species (Amidostomum anseris, Amidostomum spatulatum, Drepanidotaenia lanceolata, Epomidiostomum crami, Heterakis dispar, Notocotylus attenuatus, Tetrameres striata, Trichostrongylus tenuis, Tschertkovilepis setigera, and Wardoides nyrocae) and 1 previously undescribed trematode. All geese sampled were infected with at least one helminth species. All helminth species identified were present in both age classes and species, providing evidence of transmission at high latitudes and suggesting broad host susceptibility. Also, all but one helminth species were present at both sites, suggesting conditions are suitable for transmission across a large latitudinal/environmental gradient. Our study provides important baseline information on avian parasites that can be used to evaluate the effects of a changing climate on host-parasite distributions.