ARE FEMALE BOAT TAILED GRACKLE COLONIES NEUTRAL ASSEMBLAGES

Female boat-tailed grackles (Quiscalus major) nest in colonies, and ap parently settle independently of male activities. Associations between colony females may be mutually beneficial (cooperative hypothesis) or females may be penalized by associating (competitive hypothesis). Con trary to predictions based on either cooperative or competitive behavi or, (1) reproductive success was not related to colony size nor to int ernest distance; (2) intracolony nesting synchronies were the same as those of the whole population, and within colonies, there was no relat ionship between the timing and spacing of nearest-neighbor nests; and (3) already established females were only occasionally aggressive towa rd females attempting to settle near them, and their aggressive respon se was independent of their stage of nesting. The results suggest that females act independently of each other and do not affect each other' s fitness (neutral female hypothesis). Colonies may be neutral aggrega tions in sites secure from ground predators. Although females benefit by co-occupying predator-free sites, advantages and disadvantages of c oloniality do not appear to be related to intrasexual association.