Behavioural adjustments in the social associations of a precocial shorebird mediate the costs and benefits of grouping decisions

Abstract

Animals weigh multiple costs and benefits when making grouping decisions. The cost‐avoidance grouping framework proposes that group density, information quality and risk affect an individual’s preference for con or heterospecific groups. However, this assumes the cost–benefit balance of a particular grouping is constant spatiotemporally, which may not always be true. Investigating how spatiotemporal context influences grouping choices is therefore key to understanding how animals contend with changing conditions. Changes in body size during development lead to variable conditions for individuals over short time‐scales that can influence their ecological interactions. Hudsonian godwits Limosa haemastica, for instance, form a protective nesting association with a major predator of young godwit chicks, colonial short‐billed gulls Larus brachyrhynchus. Godwit broods may avoid areas of higher gull densities when chicks are susceptible to gull predation but likely experience higher risk from alternative predators as a result. Associating with conspecifics could allow godwits to buffer these costs but requires enough other broods with whom to group. To determine how age‐dependent predation risk and conspecific density influence godwit grouping behaviours, we first quantified the time‐dependent effects of con‐ and heterospecific interactions on the mortality risk for godwit chicks throughout development. We then determined how godwit density and chick age affected their associations with con‐ and heterospecific. We found that younger godwit chicks' survival improved with closer association with conspecifics, earlier hatch dates and lower gull densities, whereas older chicks survived better with earlier hatch dates, though this effect was less clear. Concomitantly, godwit broods avoided gulls early in development and when godwit densities were high but maintained loose associations with conspecifics throughout development. We identified how individuals can optimally shift with whom they group according to risks that vary spatially and temporally. Investigating the effects of a species' ecological interactions across spatiotemporal contexts in this way can shed light on how animals adjust their associations according to the costs and benefits of each association.

Dynamic sensitivity to resource availability influences population responses to mismatches in a shorebird

“…We relocated radio‐tagged chicks an average of 4.3 times (SD = 2.71, range = 1–19; n = 778) and recaptured them 1.5 times (SD = 0.83; n = 103). In most cases of chick death ( n = 89), we located a carcass (37%) or found a detached radio (20%) in habitats clearly suggestive of predators (e.g., on a gull nesting island) within an average of 2 days (range = 0–4 days) of the first failed relocation attempt (Wilde, Swift, & Senner, 2022).…”

“…We constructed a logit-linear mixed model to estimate the additive effects of (1) daily invertebrate biomass, (2) daily invertebrate body mass, (3) hatch date, and (4) age along with random intercepts for (5) brood ID, (6) year, and (7) study plot. We included age, rather than a measure of metabolic rate, to account for both increasing energy demands (Williams et al, 2007) and other age-related foraging behaviors (e.g., functional responses), as well as the fact that different predators prey on godwit chicks of different ages (Wilde, Swift, & Senner, 2022). We averaged our continuous parameters across 3-day periods (i.e., our relocation interval) and standardized all variables by subtracting the mean and dividing by two SDs (Gelman, 2008).…”

“…Despite mismatches affecting the survival of individual godwit chicks in Hudson Bay, there have been few apparent population level consequences (Senner et al, 2017). Furthermore, much of the interannual variation in the fledging rates of Alaskan godwits is not explained by predation or density-dependent processes (Senner et al, 2017;Swift et al, 2017aSwift et al, , 2019Wilde, Swift, & Senner, 2022). The observed variation in the fledging rates of Alaskan godwits may instead result from a potential correlation between early snowmelt and low annual fledging rates, suggesting that heretofore undocumented mismatches may be affecting godwits' annual reproductive output (Saalfeld et al, 2019).…”

Consistent apparent adult survival and nest‐site fidelity of whimbrel Numenius phaeopus near Churchill, Manitoba, Canada over a 40 year period

“…Arctic and subarctic breeding species are also rarely able to raise more than one brood during the brief summer (Jamieson 2011, Saalfeld et al 2021). Additionally, shorebirds have relatively low hatching (Ricklefs 1969, Smith et al 2007) and fledging success rates (Loonstra et al 2019, Wilde et al 2022), largely due to predation (Smith et al 2012, Wilde et al 2022).…”