Chick parasitism by blowflies affects feeding rates in a Mediterranean population of blue tits

Offspring fitness depends on interactions between parental care and environ mental constraints. It has been suggested that in altricial birds parents a re able to compensate for the detrimental effects of ectoparasites by impro ving food provisioning. We tested this prediction in a population of blue t its highly parasitized by blowfly larvae. The frequency of parental feeding visits was significantly higher in parasitized broods than in broods exper imentally deparasitized. Despite a strong increase in parental care, chicks of parasitized broods were lighter, smaller, and more anaemic than chicks in deparasitized broods. Parents invest more in feeding parasitized young b ut cannot fully compensate for the negative effects of parasites, hence you ng are in poor condition at fledging.