Factors Influencing Occupancy Of Nest Cavities In Recently Burned Forests

Recently burned forests in western North America provide nesting habitat for many species of cavity-nesting birds. However, little is understood about the time frame and the variables affecting occupancy of postfire habitats by these birds. We studied factors influencing the occupancy and reuse of nest cavities from 1-7 years after fire in two burned sites of western Idaho during 1994-1999. Tree cavities were used for nesting by 12 species of cavity nesters that were classified by the original occupant (strong excavator, weak excavator, or nonexcavator) of 385 nest cavities. We used logistic regression to model cavity occupancy by strong excavators (n = 575 trials) and weak excavators (n = 206 trials). Year after fire had the greatest influence on occupancy of nest cavities for both groups, while site of the burn was secondarily important in predicting occupancy by strong excavators and less important for weak excavators. Predicted probability of cavity occupancy was highest during the early years (1-4) after fire, declined over time (5-7 years after fire), and varied by site, with a faster decline in the smaller burned site with a greater mosaic of unburned forest. Closer proximity and greater interspersion of unburned forest (15% unburned) may have allowed a quicker recolonization by nest predators into the smaller burn compared to the larger burn with few patches of unburned forest (4% unburned). In combination with time and space effects, the predicted probability of cavity occupancy was positively affected by tree and nest heights for strong and weak excavators, respectively.Original Abstract: Los bosques del oeste de America del Norte que han sido recientemente quemados proveen habitat de nidificacion para muchas especies de aves que nidifican en cavidades. Sin embargo, se sabe poco sobre el marco temporal y las variables que afectan la ocupacion por parte de las aves de los habitats luego del fuego. Entre 1994 y 1999, estudiamos los factores que influencian la ocupacion y el uso repetido de las cavidades de nidificacion entre 1 y 7 anos luego del fuego, en dos sitios quemados en el oeste de Idaho. Las cavidades de los arboles fueron usadas para nidificar por 12 especies de aves, las que fueron clasificadas (385 cavidades) segun el ocupante original (excavador fuerte, excavador debil y no excavador). Usamos regresion logistica para modelar la ocupacion de las cavidades por parte de excavadores fuertes (n = 575 pruebas) y debiles (n = 206 pruebas). El