Nutritional state variations in a tropical seabird throughout its breeding season

Abstract

Individual body condition is frequently used to explain differences in foraging and breeding ecology in seabirds. However, little is known about the covariations of body mass with the nutritional state of animals as measured through plasma metabolites and how these different measures vary between and within individuals during breeding. Here, we assessed intra-individual variations of plasma metabolites (triglycerides, cholesterol, protein, and ß-hydroxybutyrate concentrations) and in body mass of Blue-footed boobies (Sula nebouxii) throughout their breeding season 2011-2012 in Isla El Rancho, Mexico. We found breeding-stage and sex-specific variations in individuals' plasma metabolite concentrations, but these did not mirror variations in body mass. Before egg-laying, females had higher triglycerides, cholesterol, and protein concentrations than males. In contrast, males used their nutritional reserves (higher ß-hydroxybutyrate concentrations) more than females during the breeding season (except for early chick-rearing). At the individual level, males gained weight during the breeding season, whereas females lost weight. We also found that between-individual differences in plasma metabolite concentrations and changes in body mass were not consistent throughout the breeding season, while individual body mass was significantly repeatable. This study contributes to a better understanding of seabird breeding ecology and physiology by showing that sex-specific breeding roles might highly influence the nutritional state. Similar patterns might occur in other seabird species, helping to explain why we can find stage- and sex-specific foraging behaviors even in monomorphic species.

Keywords: Cholesterol; Reproduction; Seabirds; Sex; Triglycerides; ß-hydroxybutyrate.

Fig. 1

Plasma metabolite concentrations, body mass, and body mass changes (Δ_BM) of female and male Blue-footed boobies (Sula nebouxii) during the breeding season 2012 at Isla El Rancho, Mexico. Plasma metabolites presented are triglycerides (n = 116), total proteins (n = 104), cholesterol (n = 114), and ß-hydroxybutyrate (n = 108). Body mass (n = 118) and Δ_BM (n = 80) are included. Means (± standard error) and individual values are presented

Fig. 2

Individual plasma metabolite concentrations, body mass, and changes in body mass (Δ_BM) of Blue-footed boobies (Sula nebouxii) during the breeding season 2012 at Isla El Rancho, Mexico. Only individuals that were sampled at all four stages of breeding are included. Plasma metabolites presented are triglycerides (female = 9, male = 11), total proteins (female = 7, male = 5), cholesterol (female = 8, male = 11), and ß-hydroxybutyrate (female = 8, male = 8). Body mass and Δ_BM are included (female = 9, male = 11). Individual concentrations and trajectories are presented (females in circles and filled lines, males in triangles and dashed lines)