Data from: Sexual dimorphism does not translate into foraging or trophic niche partitioning in Peruvian boobies (Sula variegata)

Intraspecific competition can lead to sexual segregation of diets or foraging behaviors in seabirds, and in some species the resulting niche partitioning is facilitated by sexual dimorphism. However, environmental stochasticity can mediate intraspecific competition and thus the extent of sex-based partitioning. The Peruvian booby (Sula variegata) is a sexually dimorphic seabird endemic to the Humboldt Current System (HCS), a highly variable environment due to El Niño Southern Oscillation. To determine the extent of sexual partitioning in this species, we quantified the foraging and trophic niches of breeding Peruvian boobies at Isla Guañape Norte, Peru in two years with different oceanographic conditions and nesting propensity. Morphometrics, GPS-tracked foraging behaviors, diets via regurgitates, and isotopic niches were compared between sexes and years. We expected few sex-based differences during neutral conditions (2019) and more evident partitioning during El Niño conditions (2016). Although females were larger and in better body condition than males in both years, breeding Peruvian boobies in our study did not exhibit sex-specific foraging or isotopic niche partitioning and had few differences in diet. Anchoveta (Engraulis ringens) dominated male and female diets in both years, reflecting Peruvian boobies’ dependence on this prey. Overall, while oceanographic conditions in 2016 were unfavorable enough to reduce nesting propensity and increase the proportion of time spent foraging by Peruvian boobies, these effects did not translate to foraging or dietary niche partitioning between the sexes for those individuals who opted to breed. In combination, our results suggest similarly weak intraspecific competition in both 2016 and 2019, and highlight how the foraging strategies of Peruvian boobies have adapted to these conditions in the HCS.