Foraging during breeding is a demanding activity linked to breeding investment and possibly constrained by individual quality. Telomere length, the protective nucleoproteins located at the ends of the chromosomes, is considered a trait reflecting somatic maintenance and individual quality. Therefore, foraging effort and parental investment may be positively related to telomere length, if individuals with longer telomeres are of better quality and thus able to maintain better body condition and allocate more resources to parental activities. In the brown booby (Sula leucogaster), we investigated if telomere length is related to body mass (a proxy of condition) and whether variation in foraging behavior and provisioning effort is related to telomere length or body mass. Then, we explored whether variation in foraging and provisioning influences the chick mass growth rate. In 34 pairs nesting in Isla de San Jorge, in the Gulf of California, México, we sampled their blood to estimate telomere length, measured their body mass, and for 10 days, recorded their foraging behavior via global positioning system (GPS) loggers and their chick provisioning rate and chicks’ mass growth rate. We found a positive relationship between parents’ body mass and telomere length. Body mass did not affect foraging behavior. Females with longer telomeres were more prone to travel longer distances towards offshore and deeper waters than females with shorter telomeres. In contrast, males with longer telomere lengths performed more nearshore foraging trips than males with shorter telomeres. Chick provisioning rate was unrelated to telomere length or body mass, but females fed the chick at a rate 2.4 times greater than males. Females’ offshore foraging, but not males’, was positively related to chick mass growth rate. Our results suggest that individual quality, indicated by telomere length, is an important driver of sex-specific, between-individual variation in foraging behavior, indirectly affecting offspring condition.

Summary of Field Methods

The study was carried out from December 2017 to January 2018 in the brown booby breeding colony of Reserva Federal Isla de San Jorge, Sonora Mexico. 34 pairs rearing a chick were marked with a numbered flag, both parents were banded, their mass (± 20 g) were measured and a blood sample (1.5 ml) was obtained from their brachial vein using a sterile and heparinized syringe. For a subset of pairs (n = 27) foraging behavior was recorded by setting both members of a pair with a global positioning system (GPS) logger for roughly 10 days. To evaluate the potential effects of carrying a GPS logger on parental behavior, the 7 remaining focal pairs were treated identically to the birds with GPS, except they were not given a logger. We captured all chicks from focal nests to obtain a blood sample (1 ml) for sex determination and measured their beak (± 0.1 mm), ulna (± 1 mm) and mass (± 1 g), once when their parents were initially captured and again 10 days later, to estimate mass increase during the same period when the parents were GPS tracked. Chicks’ morphological measures at first capture were used to calculate their age (mean age = 26, range = 20 – 32 days) using growth curves from brown booby chicks of known age previously recorded by our group. We performed behavioral observations during the 10 days when the birds were GPS tracked to determine parental provisioning.

From adult blood samples we calculated the relative telomere length of individuals by real-time qPCR following a protocol previously reported for our study species (Guillen-Parra et al. 2024).