Site fidelity and the demographic implications of winter movements by a Migratory Bird the Harlequin Duck (Histrionicus)

Iverson, Samuel
Esler, Daniel
Centre for Wildlife Ecology, Simon Fraser University Delta BC
Publication Date: 

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 km 2 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 11.59 / 2.2 km 2 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

Citation Information: 
J. Avian Biol. 37: 219-228