Energetic constraints drive sex-specific parental care in the monomorphic Leach's storm-petrel Hydrobates leucorhous

Sex-specific parental care in dimorphic species may be unsurprising, but why this occurs in monomorphic species is more puzzling. To date, however, there have been few examinations of the causes of this phenomenon. Here, we evaluated possible explanations of sex-specific provisioning in the monomorphic Leach's storm-petrel Hydrobates leucorhous (until recently Oceanodroma leucorhoa). We tracked the chick-rearing behavior of 74 mated pairs using an automated nest monitoring system and collected daily measurements of chick growth. We found that males provisioned more frequently and made a larger overall contribution to chick feeding than females. Within-individual trip duration was more variable for females, suggesting that they were alternating to a greater degree between short, energetically taxing trips that prioritize chick care and longer, recovery trips that prioritize self-care. Moreover, females were more likely to embark on longer trips after completing a short trip and after encountering a chick in good condition. Males, however, appeared better able to perform repeated short trips that resulted in more frequent provisioning as well as greater amounts overall. These findings are consistent with the explanation that energetic constraints on females give rise to male-biased, sex-specific provisioning in a monomorphic species and are likely to explain similar patterns in other long-lived species where adult survival is high.

Automated summary

This study examined sex-specific provisioning in the monomorphic Leach's storm-petrel and found that males provisioned more frequently and made a larger overall contribution to chick feeding than females. Females showed more variable trip durations, suggesting they alternated between short, energetically taxing trips for chick care and longer recovery trips for self-care. These findings suggest that energetic constraints on females lead to male-biased, sex-specific provisioning in monomorphic species.