BEGGING, FOOD PROVISIONING, AND NESTLING COMPETITION IN GREAT TIT BROODS INFESTED WITH ECTOPARASITES

Ectoparasites are a ubiquitous environmental component of breeding bir ds, 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 a cting on the hosts will favor physiological and behavioral responses t hat 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 r esponse 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 cu rrent brood. Since the nestlings are weakened by the ectoparasites the y may beg less, but on the other hand they may beg more in order to ob tain more food. In this study we show experimentally that (1) hen flea s (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 frequenc y of feeding trips by over 50%, (4) the females do not adjust feeding rate to the lowered nutritional state of nestlings, and (5) food compe tition among siblings of parasitized broods is increased. Ultimately t he difference in the parental feeding response may be understood as th e result of a sex-related difference in the trade-off of investing in current versus future broods.