EFFECTS OF HEMATOPHAGOUS ECTOPARASITES ON NESTLING HOUSE WRENS, TROGLODYTES-AEDON - WHO PAYS THE COST OF PARASITISM

We experimentally investigated the effects of two haematophagous ectoparasites, larvae of the blow fly Protocalliphora parorum (Diptera: Calliphoridae) and the mite Dermanyssus hirundinis (Mesostigmata: Dermanyssidae), on the survival, health and growth of nestling house wrens Troglodytes aedon. Nestlings in broods with relatively heavy infestations (> 10 larvae, and hundreds to thousands of mites, per nestling) did not have higher mortality, reduced growth of tarsi and primary feathers, or lower pre-fledging hematocrits than nestlings occupying nests in which parasites were killed with heat. Infested nestlings approached their peak mass at a slightly slower rate than uninfested nestlings. Infested nestlings may also have lost slightly less mass late in the nestling stage when mass normally recesses as maturing tissues lose water. Overall, parasites had surprisingly little direct effect on nestlings, even though they consumed an estimated 10-30 g of blood per brood before nestlings fledged. This suggests that parents increase their own energy expenditure to compensate for the effects of larval feeding. If parasites increase the cost of reproduction for host parents, parasites may influence certain life-history characteristics such as clutch size in the host population.