Nestling begging intensity and parental effort in relation to prelaying carotenoid availability

Carotenoids are antioxidants playing major roles in physiologicalfunctions at various stages of an animal's life. Female birdsdeposit large amounts of carotenoids into their eggs. Carotenoidsare, however, a limiting resource, and females are expectedto balance carotenoid deposition into the eggs with their utilizationfor themselves. Carotenoid availability is thus likely to determineboth the levels of yolk carotenoids and maternal care duringrearing. Carotenoids have been shown to benefit the embryo andthe growing nestling, and it can be hypothesized that an increasein carotenoid availability during laying leads to higher nestlingcondition and competitive ability. We manipulated carotenoidavailability to great tit pairs prior to and during egg layingand later partially cross-fostered chicks at hatching. Duringthe rearing period, we measured how carotenoid availabilityaffected nestlings begging behavior and male and female feedingeffort. We also manipulated the ectoparasite load, predictingthat carotenoid supplementation would help adults and nestlingto cope with parasites. Nestlings hatched from eggs laid bycarotenoid-supplemented females and raised in small broods beggedmore intensely. Nestlings in small deparasitized broods alsobegged more actively. The feeding effort of control femalesincreased with brood size, whereas the feeding effort of carotenoid-supplementedfemales was high whatever the brood size. Male feeding effortwas unaffected by our treatment. Our results support the hypothesisthat maternally derived carotenoids increase nestling beggingbehavior and hence competitive ability. They further suggestthat carotenoid availability determines the level of parentalinvestment and can mediate trade-offs between life-history traits.