State uncertainty models and mark‐resight models for understanding non‐breeding site use by Piping Plovers

Abstract

Conservation of beach‐nesting medium‐distance migrants has focused on breeding areas because protection of nests is more tractable than protection of non‐breeding habitat. As breeding ground management has encountered diminishing returns, interest in understanding threats in non‐breeding areas has increased. However, robust estimates of non‐breeding demographic rates and abundance are generally lacking, hindering the study of limiting factors. Estimating such rates is made more difficult by complex population dynamics at non‐breeding sites. In South Carolina, endangered Piping Plovers Charadrius melodus start arriving in July and some depart prior to December (the autumn‐only population) while others remain through at least March (the wintering population). State uncertainty capture‐mark‐recapture models provide a means for estimating vital rates for such co‐occurring populations. We estimated the proportion of the population entering the study area per survey (entry probability) and proportion remaining per survey (persistence rate) for both populations during autumn, and abundance of the wintering population, at four sites in South Carolina in 2006/7 and 2007/8, taking advantage of birds previously colour‐ringed on the breeding grounds. We made fairly precise estimates of entry and persistence rates with small sample sizes. Cumulative entry probability was ~50% by the end of July and reached 95% for both populations by October. Estimated stopover duration for birds in the autumn‐only population was 35 days in year 1 and 42 days in year 2. We estimated a wintering super‐population size of 71 ± 16 se birds in the first year and 75 ± 16 in the second. If ringing programmes on the breeding grounds continue, standardized resighting surveys in the non‐breeding period and mark‐recapture models can provide robust estimates of entry and persistence rates and abundance. Habitat protection intended to benefit non‐breeding Piping Plovers at our coastal sites should be in effect by late summer, as many birds are resident from July to the end of winter.

Making use of multiple surveys: Estimating breeding probability using a multievent‐robust design capture–recapture model

“…Because these secondary occasions provide a second source of information on capture probabilities, robust design often yields more identifiable parameters with less bias and better precision compared to traditional capture–recapture approaches (Kendall & Nichols, ). As with multievent models, state uncertainty can be incorporated in both the closed (Kendall, Hines, & Nichols, ) and open robust design (Cohen et al., ; Ruiz‐Gutierrez, Kendall, Saracco, & White, ) parameterizations. One of the generalizations of the classic robust design, the Barker/robust design (Kendall et al., ), combines recapture data collected under a robust design framework with auxiliary resightings or dead recoveries made at any time and place.…”

Quantifying phenology and migratory behaviours of hummingbirds using single-site dynamics and mark-detection analyses

“…We used a novel multi-state model with state uncertainty to examine migratory strategies of coexisting Anna’s and Allen’s hummingbirds, and compared with obligate migratory black-chinned hummingbirds. Because the models probabilistically assign individuals to unobservable states, these multi-state models are powerful tools for quantifying population structures among animals adopting diverse seasonal movement strategies [ 31 , 34 ]. We analysed data from two sites, in northern and southern California, USA, to determine if proportional composition of migrants and residents was species- or population-specific.…”