For twelve years the PIs have studied several populations of wrens (Campylorhynchus griseus) that practice cooperative breeding in Venezuela. These birds live in extended family groups on permanent communal territories, a habit that is widespread among tropical birds. These populations are an especially revealing test case of the above evolutionary ideas about cooperation because it so effectively increases the number of young that can be produced. Genealogies are available for 85 groups (more than 700 marked individuals) of this species in two distinct habitat types. Using newly-developed DNA fingerprinting techniques, the PIs will establish whether the presumed breeders are the only birds reproducing in these family groups, and whether putative nonbreeding helpers are aiding in rearing siblings. This test will now be based on conclusive evidence from the genetic material itself rather than on fallible inferences based on behavioral observation. They will document the extent to which parentage is shared within and between groups, and analytical models and computer simulations will quantify the potential importance of parentage shared beyond a principal pair in social groups. They will continue field experiments examining the processes of competition for productive breeding positions and group defense against predators, the suspected mechanism of the advantage of breeding in a group. They will also explore the implications of short-distance dispersal for the genetic structure and distinctness of populations, using restriction- fragment-length polymorphism (RFLP) analyses and our long-term data on differences in dispersal tendencies between populations.
