Responses of cavity-nesting birds to fire: Testing a general model with data from the Northern Flicker

Abstract

Census-based studies document changes in population size of animal species in response to wildfires, but mechanisms involving behavior of individuals and the effects on reproductive success are usually unknown. I developed a conceptual model explaining the persistence of cavity-nesting birds on the landscape after fires depending on carrying capacity (food supply) of the habitat and the philopatry and territoriality of the species. The breeding density, nest site characteristics, and reproductive success of Northern Flickers Colaptes auratus was studied before and after low- to moderate-severity fires on replicated plots. The density and spatial distribution of nests did not change in a consistent way after fires, but the rates of cavity excavation increased and characteristics of nest sites changed as such decay class of the tree. Laying dates were delayed and clutches were smaller in freshly excavated vs. reused cavities on the burned sites. Breeding philopatry caused a shift to older age classes in the population. Depredation of nests by small mammals increased during the first three years after fires, reducing the number of young produced per nest attempt on burned plots. The study shows that, even when fire does not reduce the density of breeding pairs, there may be detrimental effects detected only by monitoring the behavior and reproduction of individuals.