Virginia A. Somes, A Model for the Dynamics of the Pygmy Nuthatch (Sitta pygmaea) and Ponderosa Pine Snags in Managed Forest Lands.

Abstract: This study employed two computer simulation models to investigate the viability of a population of pygmy nuthatches (Sitta pygmaea) in a ponderosa pine forest in Arizona. Pygmy nuthatches are secondary cavity nesters and rely heavily on cavities in snags for roosting and nesting purposes. Therefore, the models incorporated ponderosa pine tree and snag dynamics. One model examined a population of pygmy nuthatches in a landscape of uniform habitat. The other model examined a population of pygmy nuthatches in landscape containing three regions of different habitat. This model simulated events occurring near Flagstaff, Arizona. Actual geography of a portion of the Coconino National Forest was approximated in the simulation by use of a hexagonal grid, and dispersal between the three different habitat regions was modeled by moving individuals in discrete steps on the grid. Demographic parameters, competition, habitat conditions, timber harvest conditions, dispersal, and introduction of nest boxes were examined. The results indicated that densities of both snags as well as ponderosa pine trees>200 years are important indicators of good habitat conditions for the pygmy nuthatch. When either of these densities are too low, the population can not sustain itself at a viable level. Timber harvests generally decrease both of these densities. Nest boxes can artificially take over the role of snags, but they only increase the population densities significantly if the density of ponderosa pine>200 years is sufficiently high.

Justin E. Heavilin, A Model of Intraspecific Competition for a Dynamically Modeled Resource.

Abstract: