HEARTWOOD DECAY AND VERTICAL-DISTRIBUTION OF RED-NAPED SAPSUCKER NEST CAVITIES

This paper describes a dynamic spatial pattern of Red-naped Sapsucker (Sphyrapicus nuchalis) cavity excavation in aspen groves and evaluates the possible importance of heartwood decay distribution, a prerequisite for nest excavation, in producing it. Sapsuckers typically situate the first cavity excavation in a tree relatively close to the ground and then make progressively higher excavations in subsequent years. Heartwood decay is reported to infect aspen via the roots or broken branch stubs, mostly at the base of the trees. Coring revealed that all nest trees were rotted at the base. The pattern of sapsucker cavity excavation can be explained as the outcome of an interaction between the distribution over height within trees of both heart rot and predation risk.