Wintering, rather than breeding, oceanic conditions may modulate declining survival in a long-distance migratory seabird

Katherine R. S. Snell; Inês Alexandre Machado dos Santos; Rob S. A. van Bemmelen; Børge Moe; Kasper Thorup

doi:10.3354/meps14783

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MEPS 754:93-103 (2025) - DOI: https://doi.org/10.3354/meps14783

Wintering, rather than breeding, oceanic conditions may modulate declining survival in a long-distance migratory seabird

Katherine R. S. Snell^1,2,3^,^#^,*, Inês Alexandre Machado dos Santos¹^,^#, Rob S. A. van Bemmelen^4,5, Børge Moe⁶, Kasper Thorup^1,7

¹Center for Macroecology, Evolution and Climate, Globe Institute, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen, Denmark
²Max Planck Institute of Animal Behavior (MPI-AB), Am Obstberg 1, Radolfzell 78315, Germany
³Centre for the Advanced Study of Collective Behaviour, University of Konstanz, Konstanz 78464, Germany
⁴Waardenburg Ecology, Culemborg, 4101 CK, The Netherlands
⁵Wageningen Marine Research, IJmuiden, 1976 CP, The Netherlands
⁶Norwegian Institute for Nature Research (NINA), Trondheim 7485, Norway
⁷Copenhagen Bird Ringing Centre, Natural History Museum of Denmark, University of Copenhagen, Øster Voldgade 5-7, 1350 Copenhagen, Denmark

*Corresponding author: ksnell@ab.mpg.de
^#These authors contributed equally to this work

ABSTRACT: Steep declines in Arctic skua populations in the southern extent of their breeding range have been reported during the last half of the 20^th century. We used 24 yr of ringing and re-encounter data from the Faroe Islands, North Atlantic, to investigate if patterns in survival probabilities can be explained by large-scale climatic events. Having first determined the migratory phenology and wintering regions, we estimated the effects of the North Atlantic Oscillation (NAO) index on survival during breeding and the Oceanic Niño index (ONI) during the non-breeding period within a capture-mark-recapture framework. Temporal trends along with direct and time-lagged effects of the environment on annual survival were modelled. We found support for a substantial decrease in adult annual survival, from ca. 0.93 in 1985 to ca. 0.77 in 2008, and weak support for a decrease in young (first year) survival over the duration of the study period. Furthermore, models indicated increased young survival following an El Niño winter. We suggest this time-lagged effect reflects downstream propagation of environmental conditions, particularly food availability, or a potential carry-over effect of El Niño conditions positively impacting the performance of the parents in the subsequent breeding season, leading to improved young survival prospects. While adult mortality cannot be attributed to the oceanic climate oscillations tested here, the negative trend in survival may account for the substantial population declines observed over the last decades.

KEY WORDS: Mortality · Carry-over effects · CMR modelling · Stercorarius parasiticus

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Cite this article as: Snell KRS, Machado dos Santos IA, van Bemmelen RSA, Moe B, Thorup K (2025) Wintering, rather than breeding, oceanic conditions may modulate declining survival in a long-distance migratory seabird. Mar Ecol Prog Ser 754:93-103. https://doi.org/10.3354/meps14783

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MEPS 754:93-103 (2025) - DOI: https://doi.org/10.3354/meps14783

Wintering, rather than breeding, oceanic conditions may modulate declining survival in a long-distance migratory seabird

Katherine R. S. Snell1,2,3,#,*, Inês Alexandre Machado dos Santos1,#, Rob S. A. van Bemmelen4,5, Børge Moe6, Kasper Thorup1,7

Katherine R. S. Snell^1,2,3^,^#^,*, Inês Alexandre Machado dos Santos¹^,^#, Rob S. A. van Bemmelen^4,5, Børge Moe⁶, Kasper Thorup^1,7