Survival during the pre-fledging period rather than during post-fledging drives variation in local recruitment of an end
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ORIGINAL ARTICLE
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 Pakanen1,2 · Robin Hagstedt1 · Angela Pauliny1 · Donald Blomqvist1 Received: 20 February 2020 / Revised: 19 July 2020 / Accepted: 30 August 2020 © The Author(s) 2020
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. Keywords Baltic dunlin · Capture-recapture · Juvenile survival · Precocial · Shorebird Zusammenfassung Das Überleben vor, nicht nach dem Flüggewerden führt bei einem bedrohten Küstenzugvogel, dem Südlichen Alpenstrandläufer (Calidris alpina schinzii), zu Unterschieden in der Ortstreue der Jungtiere Man geht davon aus, dass der Rückgang der in Feuchtwiesen brütenden Küstenvogelpopulationen in erster Linie auf Veränderungen in der Fortpflanzung zurückzuführen ist. Zwar gibt es viele Ergebnisse zum Überleben im Nest, aber aufgrund der verzerrenden Effekte durch viele Abwandernde, die dauerhaft wegbleiben, gibt es nur wenig zuverlässige Informationen über die ortstreuen Tiere. Außerdem konnten nur wenige Studien die Auswirkungen des Überlebens vor und nach dem Flüggewerden auf die Ortstreue untersuchen. Deshalb ist unklar, ob die die Ortstreue der Jungen von den Verhältnissen am Brutplatz oder von denen an anderen Orten, an denen nicht gebrütet wird, abhängt. Wir untersuchten an einer isoliert lebenden Population des Südlichen Alpenstrandläufers (Calidris alpina schinzii), der an der schwedischen Westküste brü
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