|Abstract or Summary
- Studies of avian movement ecology afford essential insights regarding species' life histories, population dynamics, habitat and resource requirements, and other ecological relationships. While it is widely recognized that events in different stages of the annual cycle have important implications for processes in avian ecology, evolution, and conservation, challenges associated with quantifying migratory connectivity frequently constrain annual-cycle approaches to the study of avian movement. The majority of cross-seasonal movement studies have been conducted to either (1) establish linkages between geographically distinct wintering, breeding and migratory stopover locations; or (2) assess site fidelity and movement within fractions of the annual cycle (i.e. individual seasons). Far fewer studies employ annual-cycle approaches to investigate how local and regional movement patterns of individuals change seasonally within an area of breeding and wintering-range overlap.
Within western Oregon’s Willamette Valley in 2007, I quantified the intra- and inter-seasonal movement patterns, fidelity (regional/local), and migratory strategies of 37 radio-marked Wilson’s Snipe (Gallinago delicata) to elucidate residency status in a region of breeding and wintering-range overlap. Available evidence indicated the potential for a variety of possible migratory behaviors for this relatively understudied migratory species; results revealed that the group monitored constituted winter residents (74%), winter transients (14%), summer residents (9%), and one year-round resident breeder (3%). Findings indicated a lack of connectivity between populations captured during winter and summer, scant evidence of partial migration (one year-round resident), as well as the first documentation of between-season fidelity of snipe to the region (return of winter resident in subsequent fall). Spring migration chronology of radio-marked winter residents indicated a strong sex differential in timing of migration, with males departing an average of 9.68 days earlier than females (20.11 days including winter transients). In contrast, fall migration patterns were suggestive of inverse chronology (females departing before males). Male-biased winter sex ratios were consistent with observed latitudinal clines for other nonbreeding shorebird populations. The protracted spring migration periods resulted in gradual dispersal consistent with energy minimization migration strategies.
Across seasons, the extent of movements and use of multiple wetland sites suggested that snipe were capable of exploratory movements, but more regularly perceived local and fine-scale segments of the landscape as connected. There were no differences in the areal extent of individual home-ranges, number of sites visited, individual mobility, or distances detected from capture sites by individual sex (or interaction of sex × season). However, movements differed significantly by season and residency, with individuals exhibiting contracted movements during late winter, and most expansive movements during precipitation-limited periods (late spring, summer, fall 2007). Mean home-range size was 3.52 ± 0.93 km2 (100% MCP) and 1.57 ± 0.42 km2 (95% fixed kernel), and did not vary by sex; however, home-range varied markedly by season (range 100% MCP = 1.04 – 7.56 km2). Overall results indicated variable fidelity patterns (e.g., prolonged periods of within-season residency, transient behavior, between-season fidelity, partial migration), which were indicative of a complex regional population structure.
Wilson’s Snipe demonstrated striking differences in movement patterns, vagility and local site fidelity across seasons in the Willamette Valley, while previous studies of shorebird movement and habitat use in the region focused solely on winter and precipitation-copious periods. Furthermore, by highlighting the seasonal changes in snipe movement metrics, this study provides the first cross-seasonal profile of a shorebird species’ space-use in a region of breeding and wintering-range overlap. Results provide insight on the regional and local fidelity and movement patterns of shorebirds in a spatiotemporally dynamic wetland landscape, across multiple seasons. Furthermore, findings indicate that single-season approaches to wetland management in the region present the risk of mischaracterizing species’ spatial requirements, and highlight the need to consider: (1) cross-seasonal effects, and (2) inter-specific differences in shorebird life histories when developing regional wetland conservation plans.