Energetic constraints drive sex‐specific parental care in the monomorphic Leach's storm‐petrelHydrobates leucorhous

Abstract

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.

Female and male Leach's Storm Petrels (Hydrobates leucorhous) pursue different foraging strategies during the incubation period

“…Leach's Storm Petrel eggs are 20-25% of adult bodyweight (Montevecchi et al 1983, Bond & Hobson 2015, Pollet et al 2020, possibly resulting in unique energetic or nutrient demands for females. Differences in male and female investment skew the opposite direction after egg-laying: compared with females, male Leach's Storm Petrels have been shown to incubate the egg for a greater proportion of time, to abandon a non-hatching egg less quickly and to maintain greater daily mean food deliveries to chicks (Mauck et al 2011, Tyson et al 2022. To date, it is unclear how these biases in offspring investment are tied to differences in the actual foraging activity of Leach's Storm Petrel parents.…”

“…2011 , Tyson et al . 2022 ). To date, it is unclear how these biases in offspring investment are tied to differences in the actual foraging activity of Leach's Storm Petrel parents.…”