Effect of an ectoparasite on lay date, nest-site choice, desertion, and hatching success in the great tit (Parus major)

Ectoparasites are common in most bird species, but experimental evidence of their effects on life-history traits is scarce. We investigated experimentally the effects of the hematophagous hen flea (Ceratophyllus gallinae) on timing of reproduction, nest-site choice, nest desertion, clutch size, and hatching success in the great tit (Parus major). When great tits were offered a choice on their territory between an infested and a parasite-free nest-box, they chose the one without parasites. When there was no choice, the great tits in a territory containing an infested nest-box delayed laying the clutch by 11 days as compared with the birds that were offered a parasite-free nesting opportunity. The finding that there was no difference in phenotypic traits related to dominance between the birds nesting in infested boxes and birds nesting in parasite-free boxes suggests that the delay is not imposed by social dominance. Nest desertion between laying and shortly after hatching was significandy higher in infested nests. There was no difference between infested and parasite-free nests in clutch size, but hatching success and hence brood size at hatching were significantly smaller in infested nests. Nest-box studies of great tits have been seminal in the development of evolutionary, ecological, and behavioral theory, but recently a polemic has arisen in the literature about the validity of the conclusions drawn from nest-box studies where the naturally occurring, detrimental ectoparasites are eliminated by the routine removal of old nests between breeding seasons. Our study suggests that this criticism is valid and that the evaluation of the effects of ectoparasites may improve our understanding of behavioral traits, life-history traits, or population dynamics

Ectoparasite affects choice and use of roost sites in the great tit, Parus major

Many diurnal bird species roost at night in holes. As a regular visitor of a hole they are therefore a welcome host for several species of ectoparasites. The interactions of ectoparasites with the behaviour, life-history traits and population demography of their hosts are largely unknown. In the present study the effects of the haematophagous hen flea, Ceratophyllus gallinae , on the great tit's choice of winter roost site were investigated experimentally. Three experiments tested (1) whether great tits prefer a clean nestbox to one containing an old, but parasite-free nest, (2) whether they prefer a parasite-free nestbox to one infested with the haematophagous hen flea, and (3) whether they prefer not to use a nestbox when there is only an infested box available in their territory. In the first experiment there was no discrimination and both kinds of boxes were used equally often. In the second experiment the great tits clearly preferred to roost in the box without ectoparasites. In the third experiment a significantly higher proportion of the infested nestboxes were not used for roosting compared with the parasite-free boxes. Recently the validity of the conclusions drawn from nestbox studies where the naturally occurring detrimental ectoparasites are eliminated by the routine removal of old nests between breeding seasons has been questioned. This study shows that ectoparasites affect host behaviour and therefore lends support to that criticism.

Begging food provisioning and nestling competition in great tit broods infested with ectoparasites

Ectoparasites are a ubiquitous environmental component of breeding birds, and it has repeatedly been shown that hematophagous ectoparasites such as fleas and mites reduce the quality and number of offspring of bird hosts, thereby lowering the value of a current brood. Selection acting on the hosts will favor physiological and behavioral responses that will reduce the parasites' impact. However, the results of the few bird studies that addressed the question of whether parasitism leads to a higher rate of food provisioning are equivocal, and the begging response to infestation has rarely been quantified. A change in begging activity and parental rate of food provisioning could be predicted in either direction: parents could reduce their investment in the brood in order to invest more in future broods, or they could increase their investment in order to compensate for the parasites' effect on the current brood. Since the nestlings are weakened by the ectoparasites they may beg less, but on the other hand they may beg more in order to obtain more food. In this study we show experimentally that (1) hen fleas (Ceratophyllus gallinae) reduce the body mass and size of great tit (Parus major) nestlings, (2) nestlings of parasitized broods more than double their begging rate, (3) the male parents increase the frequency of feeding trips by over 50%, (4) the females do not adjust feeding rate to the lowered nutritional state of nestlings, and (5) food competition among siblings of parasitized broods is increased. Ultimately the difference in the parental feeding response may be understood as the result of a sex-related difference in the trade-off of investing in current versus future broods.