TIELEMAN, B. I.*; DIJKSTRA, T.H.; WILLIAMS, J.B.; VISSER, G.H.; KLASING, K.C.; University of Missouri – St. Louis.; University of Groningen; Ohio State University; University of Groningen; University of California, Davis: Effects of experimentally increased costs of reproduction on parental effort in the tropical house wren

According to life history theory tropical birds, with relatively high adult survival and small clutch sizes in comparison with temperate zone birds, should favor their own self-maintenance and survival over that of their offspring when confronted with extra energy demands during reproduction. This trade-off has been subject of an experiment in which we handicapped adults of the tropical house wren (Troglodytes aedon) during the nestling phase by trimming their flight feathers to increase the costs of raising nestlings. To quantify parental effort we determined parental field metabolic rate, nestling feeding frequency and nestling growth. To determine investments in self-maintenance processes we measured parental basal metabolic rate, body mass, and several immune function parameters (bactericidal ability of blood, phagocytosis, and leukocyte counts). Despite similar levels of field metabolic rate, handicapped wrens fed their offspring less frequently resulting in poorer nestling condition when compared with control birds. Parental basal metabolic rate, body mass, and immune parameters did not differ between treatments. These results indicate that when confronted with extra energy demands for work during the nestling phase, tropical house wrens compromise the outcome of the current reproductive event in order to maintain their own body condition and thereby presumably chances for future reproduction.