Microclimate of tree cavity nests: Is it important for reproductive success in northern flickers?

I measured structural characteristics of 160 Northern Flicker (Colaptes aur atus) nests at Riske Creek, British Columbia, and placed electronic data-lo ggers in a subsample of 86 nests to record internal temperatures after the flickers completed nesting. Using multiple regression, I found that the bes t predictors of a variety of nest-cavity temperature variables were tree he alth, diameter of the tree at cavity height, and orientation of the cavity. Small and dead trees showed the most extreme (maximum and minimum) tempera tures during the day, but, on average, were the coldest nests from the pers pective of incubation. South-facing cavities reached the highest temperatur es during the day, and the orientation of natural cavities was also biased towards the south. I predicted that cold nests would be energetically expen sive for adults and nestlings, and found that clutch size was positively co rrelated with mean cavity temperature. However, there did not appear to be any relationship among nest temperature and hatching or fledging success.