Clutch size relative to tree cavity size in Northern Flickers

We analysed clutch size versus nest size in 153 broods of the Northern Flic ker Colaptes auratus a woodpecker using natural cavities in British Columbi a. Canada. Larger volume cavities were less susceptible to predation and ca vity size was positively associated with the age and body size of males and with the body condition of female parents. Although clutches varied betwee n 4 and 11 eggs, and the floor area of cavities varied about 5-fold, we fou nd no relationship between clutch sire and floor area or cavity volume. To see if there were fitness consequences to clutch size relative to nest size . we examined hatching success and nestling mortality in flicker broods. Ha tching success was not related to cavity size, but crowding slightly reduce d nestling survival even when clutch size was controlled statistically. How ever, there was no effect or cavity size on the total number of nestlings f ledged. Newly excavated flicker cavities were smaller than reused cavities suggesting a cost to excavation. This cost, coupled with the minimal fitnes s consequences of overcrowding. may explain why flickers do nut adjust clut ch size to cavity size.