Parental provisioning in relation to offspring sex and sex ratio in the great tit (Parus major)

Sex-biased parental care is expected if the offspring sexes differ in their energetic needs or if they differentially affect their parents' reproductive success after independence. Furthermore, parents should adjust provisioning rate and prey size to the needs of individual nestlings and the entire brood. We investigated experimentally whether parental care in the great tit varied with individual offspring sex and brood sex ratio. We created broods of skewed sex ratio and monitored parental provisioning behaviour as number and size of prey items brought to individual young and broods. We found that male and female nestlings were fed at equal rates and with equally sized prey items independently of the brood sex ratio. The male share of provisioning did not change with offspring sex or sex ratio. However, parents brought significantly larger prey items to male biased broods with a small decline in provisioning rate such that the total amount of food brought did not change. Our findings suggest that parents did respond to manipulated brood sex ratio without distinguishing between the individual nestling sexes. Bringing larger prey items at slightly lower rates to male biased broods might reduce the cost of solicitation activities or satisfy increased needs in those broods.