Spatial relationship of resident and migratory birds and canopy openings in diseased ponderosa pine forests

A method is described for predicting the spatial distribution of individual birds using presence data. The approach is demonstrated using a statistical habitat association model developed for resident and migratory birds on a 12 ha plot of ponderosa pine (Pinus ponderosa) heavily infested with southwestern ponderosa pine dwarf mistletoe (Arceuthobium vasinatum subsp. Cryptopodum (Englemann) Hawksworth and Weins). Bird locations and densiometer readings of canopy opening were recorded on a 5 m×5 m sampling grid. Minimum threshold theory was used to fit a logistic regression model to the presence data as a function of canopy opening. Highest occupancy of birds occurred at 61% canopy density. Higher probability of birds occurred in more dense canopy than less dense. Model validation indicated that the model adequately described the spatial distribution of the presence of individual birds with respect to canopy opening. Such a model could be used to determine stand conditions that are conducive and/or necessary for certain bird species, and to characterize and quantify the likely ecological consequences of changes to stand structure caused by diseases and other small scale disturbances.