DETERMINANTS OF INTRASPECIFIC BROOD AMALGAMATION IN WATERFOWL

Intraspecific brood amalgamation in waterfowl can occur before hatchin g, when females lay eggs in the nests of conspecifics, or after hatchi ng, when females abandon their young to the care of other conspecific families. Using phylogenetic information, I examined whether evolution ary transitions to intraspecific prehatching and posthatching brood am algamation in waterfowl can be associated with certain life-history an d ecological variables. Transitions to intraspecific prehatching brood amalgamation occurred more frequently in lineages carrying the coloni al-breeding state and the cavity-nesting state. However, such transiti ons occurred equally frequently in lineages carrying different life hi stories as indexed by the ratio of clutch mass to female body mass. Th e results support the view that opportunities for successful amalgamat ion, which are thought to be higher in colonial-nesting and cavity-nes ting species, act as a proximate determinant of prehatching brood amal gamation. Transitions to posthatching brood amalgamation occurred most often in lineages carrying the prehatching brood-amalgamation state, which suggests that amalgamation after hatching represents an extensio n of amalgamation before hatching that temporally increases the window of opportunity for brood mixing.