Costs of reproduction and migration are paid in later return to the colony, not in physical condition, in a long-lived seabird

Abstract

Life history theory suggests a trade-off between costly activities such as breeding and migration and somatic self-maintenance. However, how the short-term cost of parental effort is expressed in species with a slow pace-of-life is not well understood. Also, investigating carry-over effects of migration is most meaningful when comparing migratory strategies within the same population, but this has rarely been done. We explore this hypothesis in a long-lived, pelagic seabird, the Cory's Shearwater, Calonectris borealis, where males display partial migration. By manipulating reproductive effort and taking advantage of the natural variation in migratory strategy, we investigate whether early reproductive failure and migratory strategy had implications on the physical condition of males on return to the colony the following year. We experimentally induced breeding failure from mid-incubation, tracked the over-winter movements of these males and of males that invested in parental effort, and assessed innate immunity, stress, and residual body mass the following year. Early breeding failure resulted in earlier return to the colony among all males, associated with greater probability of reproductive success. Residents had a lower tail feather fault bar intensity, an indicator of stress during the non-breeding period, compared to migrants. Reproductive effort and migratory strategy had no impact on physiological condition otherwise. Our results provide evidence that in species with a slow-pace of life, such as the Cory's Shearwater, somatic maintenance is prioritised, with the costs of reproduction and migration paid in delayed arrival date.

Environmental variability directly affects the prevalence of divorce in monogamous albatrosses

“…In seabirds, bad conditions determine higher costs of reproduction and higher breeding effort [39], causing individuals to arrive to the following breeding season later (i.e. affecting the phenology) or in a poorer physiological state [40,41]. Environmental effects on the breeding phenology of migratory species might cause asynchronous arrivals to the breeding ground between pair members [42,43], ultimately promoting divorce [44].…”

Higher mercury contamination is associated with shorter telomeres in a long-lived seabird – A direct effect or a consequence of among-individual variation in phenotypic quality?

“…The ability of birds to excrete a large part of the ingested mercury via their feathers (Furness et al, 1986) may protect them from (long-lasting) consequences on telomeres. Furthermore, in long-lived birds, such as Cory's Shearwaters, somatic maintenance is expected to be prioritized (Gatt et al, 2021b;Ricklefs and Wikelski, 2002) and accordingly, their telomere shortening is comparatively low (Sudyka et al, 2016;Bauch et al, 2020).…”

Migrants and residents of a long‐lived seabird differ in their behavioural response to a stressor

“…Resident male Cory's shearwaters were found to be more likely to be unreactive to extraction from the nest than were migrants. Within the same population, migrants and residents have also been found to differ in their physiological stress responses over the non‐breeding period, with residents showing lower feather corticosterone concentrations and fewer tail feather fault bars (Pérez et al 2016, Gatt et al 2020a). Tail feather fault bar intensity reported in Gatt et al (2020a) reflected experienced acute stress, such as antagonistic inter‐individual interactions and inclement weather (Jovani and Rohwer 2016), over the period of tail feather growth between 2017 and 2018, which coincides with the period of behavioural assessments presented here.…”

“…Within the same population, migrants and residents have also been found to differ in their physiological stress responses over the non‐breeding period, with residents showing lower feather corticosterone concentrations and fewer tail feather fault bars (Pérez et al 2016, Gatt et al 2020a). Tail feather fault bar intensity reported in Gatt et al (2020a) reflected experienced acute stress, such as antagonistic inter‐individual interactions and inclement weather (Jovani and Rohwer 2016), over the period of tail feather growth between 2017 and 2018, which coincides with the period of behavioural assessments presented here. While we do not exclude that extrinsic factors at the non‐breeding areas may be acting, our current finding, that migrant and resident males differ in their behavioural reaction to a standardised stressor at their common breeding colony, suggests that the differences in stress responses reported within this population may be, at least partly, a result of a personality trait within the population with variation in an endogenous threshold to a stress response between males of different migratory strategies.…”

“…Despite an apparent flexibility in over‐winter movements and destinations, individuals are largely faithful to a particular non‐breeding area (Dias et al 2011). Migratory males return to the colony showing signs of higher overwinter stress levels than residents, as assessed by feather corticosterone (Pérez et al 2016) and tail feather fault bar intensity (Gatt et al 2020a). This difference could either be attributed to harsher environmental conditions experienced at distant non‐breeding areas, although evidence of carry‐over effects from this is absent (Gatt et al 2020a), or to an intrinsic difference in stress responses between migrants and residents (Nilsson et al 2014).…”