RESOURCE LEVELS, REPRODUCTION AND RESISTANCE TO HAEMATOZOAN INFECTIONS

Compromise of immune function during reproduction may form a link betw een parental effort and the cost of reproduction, but the role of envi ronmental variation in structuring intra-individual life-history trade -offs has been poorly investigated. We manipulated the need for parent al effort in Eurasian kestrels, Falco tinnunculus, by food-supplementi ng broods for three nestling periods, during which the natural main fo od supply (voles) varied, and found that parental parasitaemia was inv ersely related to yearly vole densities. The level of parasitaemia in females was, however, reduced by food supplements. No effect on males was expected? as earlier work has shown that only females responded to the supplements by changing their behaviour. We show directly that th e likelihood of female parasitaemia was diminished by spending less ti me in flight-hunting, which was related to reproduction during a good vole year, to our supplementary feeding, and to being mated to a male with high parental effort. Our results represent a novel direct benefi t for females in resource-providing species, linked to female as well as offspring, wellbeing, and they provide insight into why the appeara nce of reproductive costs may be linked to gender or environmental con ditions.