Age‐related variation in non‐breeding foraging behaviour and carry‐over effects on fitness in an extremely long‐lived bird

Abstract

Abstract1. Senescence has been widely documented in wild vertebrate populations, yet the proximate drivers of age-related declines in breeding success, including allocation trade-offs and links with foraging performance, are poorly understood. For longlived, migratory species, the non-breeding period represents a critical time for investment in self-maintenance and restoration of body condition, which in many species is linked to fitness. However, the relationships between age, non-breeding foraging behaviour and fitness remain largely unexplored.2. We performed a cross-sectional study, investigating age-related variation in the foraging activity, distribution and diet of an extremely long-lived seabird, the wandering albatross Diomedea exulans, during the non-breeding period. Eighty-two adults aged 8-33 years were tracked with geolocator-immersion loggers, and body feathers were sampled for stable isotope analysis. We tested for variation in metrics of foraging behaviour and linked age-related trends to subsequent reproductive performance.3. There was an age-related decline in the number of landings (a proxy of foraging effort) during daylight hours, and a decrease in body feather δ 13 C values in older males but not females, yet this did not accompany an age-related shift in distributions. Males conducted fewer landings than females, and the sexes showed some spatial segregation, with males foraging further south, likely due to their differential utilization of winds.4. Although younger (<20 years) birds had higher foraging effort, they all went on to breed successfully the following season. In contrast, among older (20+ years) birds, individuals that landed more often were more likely to defer breeding or fail during incubation, suggesting they have lower foraging success.5. As far as we are aware, this is the first demonstration of an age-specific carry-over effect of foraging behaviour in the non-breeding period on subsequent reproductive performance. This link between foraging behaviour and fitness in late but not early adulthood indicates that the ability of individuals to forage efficiently outside the breeding period may be an important driver of fitness differences in old age.This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Sublethal effects of natural parasitism act through maternal, but not paternal, reproductive success in a wild population

“…We also found sex-specific age effects; males showed a quadratic relationship between age and breeding success (with the highest breeding success occurring at intermediate ages, and lower breeding success in the youngest and oldest birds), but females did not. This occurs in a number of wild vertebrate populations and is well documented in seabirds (Daunt et al 1999, Froy et al 2017, Clay et al 2018. The effect of age on breeding success found in males could be in part linked to their response to parasitism.…”

“…, Clay et al. ). The effect of age on breeding success found in males could be in part linked to their response to parasitism.…”

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“…Furthermore, the validity of assuming non‐breeding distributions as a replacement for juvenile and immature phases is likely species‐specific. The use of stage replacements may be more appropriate when segregation between life‐history stages is low (Clay, Pearmain, McGill, Manica, & Phillips, ; Péron & Grémillet, ). However, using stage replacements when the distribution differs markedly among stages (Campioni, Granadeiro, & Catry, ; de Grissac et al, ) may omit critical marine areas.…”

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“…During winter, BBA predominantly used the Benguela Upwelling (Figure ; Figure S2; Phillips, Silk, Croxall, Afanasyev, & Bennett, ). GHA and WA also used the south‐west Indian Ocean year‐round, with seasonal use of the south‐east Atlantic, Indian and Pacific Oceans, and for WA, the Chatham Rise east of New Zealand (Figure ; Figures S3–S4; Clay et al, ; Clay, Pearmain, McGill, Manica, & Phillips, ). WCP were predominantly distributed around the Patagonian Shelf, Brazil‐Falklands Confluence and Humboldt Upwelling off Chile (Figure ; Figure S5; Phillips, Silk, Croxall, & Afanasyev, ).…”