Abstract
Information on seabird foraging behaviour outside the breeding season is currently limited. This knowledge gap is critical as this period is energetically demanding due to post‐fledging parental care, feather moult and changing environmental conditions. Based on species’ body size, post‐fledging parental strategy and primary moult schedule we tested predictions for key aspects of foraging behaviour (maximum dive depth (MDD), daily time submerged (DTS) and diurnal dive activity (DDA)) using dive depth data collected from three seabird species (common guillemot Uria aalge, razorbill Alca torda and Atlantic puffin Fratercula arctica) from the end of the breeding season (July) to mid‐winter (January). We found partial support for predictions associated with body size; guillemots had greater MDD than razorbills but MDD did not differ between razorbills and puffins, despite the former being 35% heavier. In accordance with sexual monomorphism in all three species, MDD did not differ overall between the sexes. However, in guillemots and razorbills there were sex‐specific differences, such that male guillemots made deeper dives than females, and males of both species had higher DTS. In contrast, there were no marked sex differences in dive behaviour of puffins in July and August in accordance with their lack of post‐fledging parental care and variable moult schedule. We found support for the prediction that diving effort would be greater in mid‐winter compared to the period after the breeding season. Despite reduced daylight in mid‐winter, this increase in DTS occurred predominantly during the day and only guillemots appeared to dive nocturnally to any great extent. In comparison to diving behaviour of these species recorded during the breeding season, MDD was shallower and DTS was greater during the non‐breeding period. Such differences in diving behaviour during the post‐breeding period are relevant when identifying potential energetic bottlenecks, known to be key drivers of seabird population dynamics.
Highlights
Intrinsic factors such as age, sex, reproductive status and body size are known to constrain foraging behaviour across a wide range of taxa and play a key role in shaping time activity budgets (King 1974)
The strong bimodality in Maximum dive depth (MDD) in guillemots recorded during the preceding breeding season (Supplementary material Appendix 2) was no longer present; MDD in all species was shallower than during the preceding breeding season, despite body mass increasing after the breeding season, but Daily time submerged (DTS) was greater (Supplementary material Appendix 2)
Puffins do not provide sex-specific, post-fledging parental care and we found no evidence of marked sex differences in either MDD or DTS in July (4.01 ± 0.36 h and 3.09 ± 0.21 h for males and females respectively) or August (2.99 ± 0.21 h and 2.76 ± 0.12 h for males and females respectively)
Summary
Intrinsic factors such as age, sex, reproductive status and body size are known to constrain foraging behaviour across a wide range of taxa and play a key role in shaping time activity budgets (King 1974). A range of extrinsic factors, notably weather conditions and food availability, impact behavioural choices (Ellis and Gabrielsen 2002, Humphries et al 2004) In many cases both intrinsic and extrinsic effects exhibit temporal predictability e.g. in the timing of breeding or moult, changes in day length and likelihood of bad weather (McNamara and Houston 2008). This interplay between intrinsic and extrinsic factors has helped elucidate how birds make decisions about reproduction during this crucial life history phase (Schlaepfer et al 2002) and has been well studied in long-lived birds (Phillips et al 2017). Sex-role partitioning can lead to behavioural differences in foraging behaviour, time allocation, habitat preference and scheduling of migration (Phillips et al 2017)
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