Factors Affecting Florida Scrub-Jay Nest Survival on Ocala National Forest, Florida

摘要

One of the main populations of the Florida scrub-jay (Aphelocoma coerulescens), a federally threatened species, occurs on Ocala National Forest, Florida. We determined the nest daily survival rate (DSR) of 474 nests of Florida scrub-jays in stands subject to sand pine reforestation management after timber harvesting or wildfire on Ocala National Forest. We used the information-theoretic approach with logistic-exposure modeling to determine the most likely models to account for DSR for the incubation and nestling stages separately. The models consisted of 4 components (temporal, management, habitat, and helpers) with each consisting of one to several specific variables. In the incubation stage all the best models included the temporal component alone or in concert with the habitat, helpers, or habitat and helpers components. Model averaging in the incubation stage indicated support for the year and day x year in the temporal component and stand age in the habitat component. In the nestling stage, top models all included the temporal component alone or with helpers or habitat, helpers, and the interaction of habitat and helpers. Model averaging in the nestling stage showed support for the year, nest age, and to a lesser extent day in the temporal component and helpers. The management component, which consisted of no site preparation, wildfire burn, post-harvest burn, chop and seed, or seed only, had little influence on nest survival for the incubation or nestling stages. However, we identified several other management factors that may increase Florida scrub-jay populations despite having no effect on DSR. First, the proportion of Florida scrub-jay nests was significantly higher than expected in burned habitat based on habitat availability, indicating a potential preferred nesting habitat conducive to population growth. Second, incubation stage DSR with respect to stand age (habitat component) declined to stand age 10 yr and then began to increase, which may be attributed to the higher bird population in the prime habitat in the middle stand ages. The denser population may result in more competition for resources, and possibly may attract more predators, resulting in a lower DSR. Thus, although DSR may be lower at the mid-stand ages, the overall population may actually be optimal. Therefore, to increase the Florida scrub-jay population on Ocala National Forest, we recommend maintaining a mosaic of stands <= 20 yr of age and emphasizing natural reseeding and site preparation via burning