Survival during the pre-fledging period rather than during post-fledging drives variation in local recruitment of an endangered migratory shorebird, the Southern Dunlin Calidris alpina schinzii

Veli-Matti Pakanen,Angela Pauliny,Donald Blomqvist,Robin Hagstedt

doi:10.1007/s10336-020-01814-4

Veli-Matti Pakanen, Angela Pauliny + Show 2 more

Open Access

https://doi.org/10.1007/s10336-020-01814-4

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Abstract

The declines in wet-grassland breeding shorebird populations are considered to mainly result from changes in reproduction. While there is plenty of information on nest survival, little reliable information exists on local recruitment due to confounding effects of permanent emigration. Furthermore, few studies have been able to study the roles of pre- and post-fledging survival on local recruitment. Therefore, it is unclear whether local recruitment of young reflects conditions at the breeding sites or at non-breeding sites. We studied an isolated population of the endangered Southern Dunlin (Calidris alpina schinzii) breeding on the west coast of Sweden to examine (1) brood survival (probability of at least one chick fledging) by following broods fates and (2) local recruitment (survival from hatching to 1 year old) using capture-recapture data. We then examined how much of the annual variation in juvenile survival was explained by variation in brood survival. Brood survival was on average 0.58 (annual range 0.08–1.00) and explained 64% of variation in annual local recruitment. Still local recruitment was rather high for a shorebird (0.17, SE = 0.023), which reflects the isolated nature of the study population. Our results suggest that local recruitment seems to be mainly constrained by chick survival during the pre-fledging period. Therefore, management of breeding sites leading to increased brood survival, e.g., reducing predation on chicks, should have strong impacts on local recruitment and local population growth.

Highlights

Successful conservation of endangered populations requires detailed information on factors affecting the life history traits that determine the population growth rate
This constitutes an important lack in our understanding of population dynamics and potential management options in species such as shorebirds, as local recruitment, i.e., juvenile survival, can have a strong contribution to population growth rate (Saether and Bakke 2000)
The best model (∆QAIC = 8.7) for juvenile survival was the covariate model showing a positive linear effect of brood survival on juvenile survival (Table 1; Fig. 3; βbrood survival = 2.290, CI 0.952–3.629 on the logit scale)

Summary

Introduction

Successful conservation of endangered populations requires detailed information on factors affecting the life history traits that determine the population growth rate. Reproduction can be partitioned into nest survival, number of hatched young and local recruitment, but solid knowledge about the latter is relatively scarce. This is because local recruitment is the proportion of individuals that survive and return to their natal population, and permanent emigration caused by natal dispersal may bias estimates (Paradis et al 1998). This constitutes an important lack in our understanding of population dynamics and potential management options in species such as shorebirds, as local recruitment, i.e., juvenile survival, can have a strong contribution to population growth rate (Saether and Bakke 2000). Studying pre-fledging survival of precocial species is difficult and few long-term studies have been able to study the relative roles of pre- and post-fledging survival on local recruitment in such species (Roodbergen et al 2012)

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