Birth order, individual sex and sex of competitors determine the outcome of conflict among siblings over parental care

Abstract

Success in competition for limiting parental resources depends on the interplay between parental decisions over allocation of care and offspring traits. Birth order, individual sex and sex of competing siblings are major candidates as determinants of success in sib -sib competition, but experimental studies focusing on the combined effect of these factors on parent-offspring communication and within-brood competitive dynamics are rare. Here, we assessed individual food intake and body mass gain during feeding trials in barn swallow chicks differing for seniority and sex, and compared the intensity of their acoustic and postural solicitation (begging) displays. Begging intensity and success in competition depended on seniority in combination with individual sex and sex of the opponent. Junior chicks begged more than seniors, independently of satiation level (which was also experimentally manipulated), and obtained greater access to food. Females were generally weaker competitors than males. Individual sex and sex of the opponent also affected duration of begging bouts. Present results thus show that competition with siblings can make the rearing environment variably harsh for developing chicks, depending on individual sex, sex of competing broodmates and age ranking within the nest. They also suggest that parental decisions on the allocation of care and response of kin to signalling siblings may further contribute to the outcome of sibling competition.

Sex-Related Effects of an Immune Challenge on Growth and Begging Behavior of Barn Swallow Nestlings

“…Thus, this finding might corroborate previous finding of state sensitivity and favoritism towards needy kin in this species [25], [26], [28], [49]. On the other hand, control males begged as vigorously as their LPS male siblings, probably because male barn swallow chicks compete for food more harshly than female chicks [25], [49].…”

The Odour of Sex: Sex-Related Differences in Volatile Compound Composition among Barn Swallow Eggs Carrying Embryos of Either Sex

“…The expected fitness returns from male and female offspring can vary according to a number of factors that range from paternal/maternal genetic and/or phenotypic quality [77–80], to ecological conditions [81–83] and population sex ratio [84,85]. In the barn swallow, previous studies have shown that differential parental allocation occurs depending on offspring sex [86,87]. It has also been demonstrated that nestling vocalizations [37] and gape colouration [38] varies between the sexes.…”

Are elder siblings helpers or competitors? Antagonistic fitness effects of sibling interactions in humans

“…Both are widespread across the most studied taxa in this respect, namely insects, birds and mammals [6–8], with the prevailing strategy depending on factors within a family (e.g. sex and birth order [9]), across families (e.g. number of siblings or the quality of parental territory [4,10]) and finally, between populations or species (e.g.…”