Territorial occupancy dynamics in a forest raptor community

Abstract

A Markovian modeling approach was used to explore territorial interactions among three forest raptors coexisting in a forested natural area in southeast Spain: the booted eagle (Hieraaetus pennatus), the common buzzard (Buteo buteo) and the northern goshawk (Accipiter gentilis). Using field data collected over a period of 12years, 11 annual transition matrices were built, considering four occupancy states for each territory. The model describes transitional processes (colonization, abandonment, replacement and persistence), permits temporal variations in the transition matrix to be tested, and simulates territorial occupation for a few subsequent years. Parameters for the species and community dynamics were described in terms of turnover times and damping ratio. A perturbation analysis was performed to simulate the effects of changes in the transition probabilities on the stable state distribution. Our results indicate the existence of a stable community, largely dominated by the booted eagles, and described by a time-invariant transition matrix. Despite the stability observed, the territorial system is highly dynamic, with frequent abandonment and colonization events, although interspecific territorial interactions (the replacement of one species by another) are uncommon. Consequently, the three species appear to follow relatively independent occupancy dynamics. Simulation of potential management actions showed that substantial increases in the number of territories occupied by the less common species (goshawk and buzzard) can only be attained if relatively large increases in their reoccupation and colonization rates are considered.