Conservative and opportunistic settlement strategies in Arctic-breeding shorebirds

Abstract

Shorebirds seem to have evolved a number of strategies for adapting to and exploiting the unpredictable and inhospitable Arctic environment. Two such strategies put forth by Holmes and Pitelka suggest that species either conservatively or opportunistically select breeding locations based on local environmental conditions. “Conservative” species were characterized by strong site fidelity and territoriality, consistent population densities, relatively even spacing of individuals, and monogamous mating systems, while “opportunistic” species exhibited opposite traits and were polygamous. Here, we assessed whether 10 shorebird species consistently exhibited these settlement strategies over a 10-year period (2003–2012) near Barrow, Alaska, by comparing annual estimates of site fidelity, territoriality, and population density. Additionally, we determined the relative importance of past and current environmental and social conditions in predicting annual breeding densities of these same species. Data from 1,413 captured adults and 1,946 shorebird nests indicated that most species conformed to 1 of the 2 settlement strategies, while others exhibited traits of both strategies, and a few had settlement patterns inconsistent with that predicted for their mating system. We suggest that deviations from these strategies may occur depending on a species' location within its breeding range. For some species, however, described settlement patterns may be too simplistic. Species with the same settlement strategy seem to respond similarly to environmental cues but differently than species with the alternative strategy. However, we were unable to determine a common environmental cue for species with the same settlement strategy, although lemming abundance, overall nest survival rate, and presence of conspecifics or heterospecifics did seem to influence settlement decisions in some species. Results from this study indicate that understanding how species settle may have important consequences for implementing monitoring or conservation actions.