Differential use of similar habitat by Harlequin Ducks: trade-offs and implications for identifying critical habitat

Abstract

Interactions between ecological processes operating at different scales are critical aspects of habitat suitability requiring careful consideration in conservation planning. Our previous research indicated that local abundance and demographics of subpopulations of Harlequin Ducks ( Histrionicus histrionicus (L., 1758)), structured in 11 river canyons in northern Labrador, were influenced by predation risk from nest-site-limited raptors. At demographic extremes, where raptors were absent, Harlequin Ducks were stable at high densities, with positive-projected growth, suggesting that they were at carrying capacity and a source of emigrants. In contrast, where raptors were abundant, low density, highly variable populations of ducks approached local extinction in some years, with subsequent increases suggestive of immigration rescue effects. A comparison of resources for Harlequin Ducks indicated no differences in habitat availability among these putative “source” and “sink” subpopulations. In the present study, we used multivariate analysis to identify habitat characteristics important for home-range use within these river canyons and to develop habitat suitability indices (HSI). Despite similar habitat availability, different characteristics were locally important. In a sink where predation risk was high, only danger-reducing habitat characteristics (i.e., overhang vegetation) were identified as important, whereas invertebrates was a predominant characteristic of the source HSI. Despite similar habitat availability, HSI developed in source and sink habitats would, respectively, over- and under-estimate regional habitat availability. Informed conservation and management strategies will therefore require integrating individual trade-offs about predation risk and resources into a multiscale context.