Abstract
Very little is known about trophic ontogenetic changes over the prolonged immaturity period of long-lived, wide-ranging seabirds. By using blood and feather trophic tracers (δ13C and δ15N, and mercury, Hg), we studied age-related changes in feeding ecology during the immature phase of wandering albatrosses Diomedea exulans when they gradually change from a pure oceanic life to visits to their future breeding grounds. Immatures fed in subtropical waters at high trophic positions during moult. Between- and within-individual variations in isotopic niche were very high, irrespective of age, highlighting wide-ranging exploratory behaviours. In summer, while acting as central-place foragers from their future breeding colony, individuals progressively relied on lower trophic level prey and/or southern latitudes as they aged, until occupying a similar isotopic niche to that of adults. Immatures had exceptionally high Hg burdens, with males having lower Hg concentrations than females, suggesting that they foraged more in subantarctic waters. Our findings suggest a progressive ontogenetic niche shift during central-place foraging of this long-lived species.
Highlights
In long-lived species, young individuals have a critical impact on population dynamics through their survival and recruitment rates [1]
This study presents novel trophic ecology data of the understudied yet crucial immaturity stage of a longlived, wide-ranging seabird
This study confirms that moulting immatures fed extensively in subtropical waters, irrespective of gender, and occupied a very high trophic position [8]
Summary
In long-lived species, young individuals have a critical impact on population dynamics through their survival and recruitment rates [1]. Young individuals may need a long learning period to increase their foraging skills and body condition 2 [2] before being recruited into the breeding population [3]. This might be exacerbated in marine environments, where prey occurrence is patchy and difficult to predict, involving complex foraging skills. Ontogenetic changes in feeding ecology over the immaturity stage have been rarely quantified [4] They could be critical in shaping how immatures become adults, and explaining their prolonged breeding deferral
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