Site fidelity and the demographic implications of winter movements by a migratory bird, the harlequin duckHistrionicus histrionicus

Abstract

Understanding the degree of demographic connectivity among population segments is increasingly recognized as central to the fields of population ecology and conservation biology. However, delineating discrete population units has proven challenging, particularly for migratory birds as they move through their annual cycle. In this study, radio telemetry was used to assess movement rates among habitats by harlequin ducks Histrionicus histrionicus during the non‐breeding season in Prince William Sound, Alaska. A total of 434 females were outfitted with radio transmitters over six years of data collection, and their signals tracked by aircraft. Using a spatially nested design, it was determined that 75% of radioed females remained in the bay or coastline area where they were originally trapped, 94% remained on the same island or mainland region of Prince William Sound where they began the winter period, and 98% remained within the 4500 km2 study area as a whole. Home range analyses corroborated these findings, indicating that the scale of individual movements was small, with 95% kernel home range estimates averaging only 11.5±2.2 km2. A simple demographic model, which incorporated estimates for population size, survival, and movement rates, was used to infer the degree of independence among population segments. Immigrant females were found to contribute little to population numbers in most areas, accounting for only 4% of the adult female population at a scale of approximately 100 km2. These results have important implications for the scale of conservation action for the species and demonstrate that winter movements can have a strong influence local population dynamics.

Dual-foraging of Cory’s shearwaters in the Azores: feeding locations, behaviour at sea and implications for food provisioning of chicks

“…Following previous authors (e.g. Iversen & Esler 2006, Hamer et al 2007 we considered the 95% and 50% FKD estimates to represent the area of active use and the core area of foraging activity, respectively. To examine individual foraging trips in more detail, we used the furthest recorded location from the colony during each trip to provide information on trip destinations and we also calculated total distance travelled as the sum of distances between consecutive locations at sea.…”

Cytochrome P4501A biomarker indication of oil exposure in harlequin ducks up to 20 years after the Exxon Valdez oil spill

“…We captured wintering harlequin ducks using a floating mist net during four [22]. We assume that this level of movement had little influence on our ability to draw inferences about differences in EROD activity between areas.…”

Cytochrome P4501A biomarker indication of the timeline of chronic exposure of Barrow’s goldeneyes to residual Exxon Valdez oil

“…Because of the evidence of exposure to oil nearly a decade after the spill (Trust et al, 2000) and their potential vulnerability for exposure as long as oil remains in intertidal sediments, we compared EROD activity in Barrow's goldeneyes captured in oiled and (Iverson and Esler, 2006) and thus we assumed that movements of birds between oiled and unoiled areas were unlikely and therefore would not influence our inferences about differences in EROD activity in birds from different areas. Satellite telemetry data from adult male Barrow's goldeneye marked in Prince William Sound confirm high winter site fidelity (W.S.…”