Day length may impose an ecological constraint on chick provisioning behaviour in a high-latitude seabird

Abstract

Variation in daylight hours may shape light-dependent behaviours both across seasons and among latitudinally distinct breeding colonies. We investigated the influence of photoperiod variation on chick provisioning behaviour in a high-latitude seabird, the Manx shearwater (Puffinus puffinus), a visual hunter that forages by day but feeds its chick at night to reduce predation risk. Using a four-year geolocator dataset (2017–2020) from colonies spanning 51.7–62.0°N, comprising 71 chick-rearing periods, we found that across the chick provisioning period, adults foraged for more hours per day under longer day lengths, and foraging start times were correlated with the first hour of light availability, with earlier foraging activity recorded where day lengths were longer. By contrast, shorter nights earlier in the chick-rearing period constrained the time available for nocturnal colony visits, resulting in shorter visit durations. Similar patterns were evident across latitudes, with birds breeding at higher latitudes foraging for longer periods on average, initiating foraging earlier and spending less time at the colony. These results suggest that photoperiod can promote or restrict the time available for foraging and food delivery during chick provisioning and may influence resource delivery schedules.