Defining the phenology of early breeding behaviours of Leach’s storm petrels in the northwest Atlantic (Hydrobates leucorhous)

Abstract

Laying date is one of the most important reproductive fitness metrics in birds, as timing it well optimizes food availability and ensures the best chance at reproductive success. This is especially pertinent for Leach’s Storm Petrel, a declining seabird species in Atlantic Canada, , as they have low reproductive capacity. At present, our understanding of the timing of early reproductive behaviours for Leach’s Storm Petrels in the northwest Atlantic is minimal, limited to rough estimates of hatch date based on chick measurements. This study’s goal was to determine the timing of early breeding phenology for Storm Petrels from a dataset of geolocation sensor data (GLS) for six long-term study colonies: Kent, Bon Portage, Country, Middle Lawn, Gull, and Baccalieu islands. GLS data describes location and activity of tagged individuals through recording environmental light levels; as Storm Petrels are burrow nesting seabirds, GLS light data can determine when they occupy their burrow during the day. I aimed to characterize the timing of first burrow re-occupancy, differences in pre-laying activity between the sexes, and the lay-dates or start of incubation behaviour across the study colonies. Linear and generalized linear mixed models were run to determine if sex, colony, or year had a significant effect on breeding phenology. We found that colony significantly impacted the timing of first burrow re-occupancy and lay-date/start of incubation, with Kent Island, New Brunswick, having the earliest first burrow arrival and lay-date, and Middle Lawn, Newfoundland, having the latest of both phenologies. Year significantly impacted the timing of first burrow re-occupancy, as 2015 had the earliest arrival date. These findings indicate that when Storm Petrels return to their breeding colony, they may be influenced by global ocean climatic conditions (annual differences), but that lay-date/start of incubation is mainly influenced by localized conditions at the colony. Sex significantly impacted pre-laying burrow activity, with males visiting the burrow considerably more often and for longer periods than females, but females had a longer pre-laying exodus. Our findings may aid future research on Leach’s Storm-Petrel reproductive success by informing conservation management regarding the timing of key breeding activities. Keywords: Pre-laying exodus, timing of breeding, Procellariforms, reproductive strategies, geolocator, light sensor