Seasonal changes to arthropod abundance in successional forests of the Yucatan Peninsula, with implications for overwintering forest birds

Arthropod levels typically decline during the Neotropical dry season, potentially limiting food availability for overwintering migratory forest birds. Land clearing for agriculture may further exacerbate food shortages, as mature late successional forest is replaced with younger stages of second growth habitat. The effects of this habitat conversion on food availability for overwintering migratory forest birds, however, have been little studied. We used sweepnet and branch clipping methods to examine whether foliage arthropod levels varied across a successional forest gradient during the wet and dry seasons in the Yucatan Peninsula. We also documented the foraging behavior of two migratory insectivores, American Redstart (Setophaga ruticilla), and Magnolia Warbler (Dendroica magnolia), to determine if our collection methods accurately reflected food availability for these birds. For sweepnet collections, late successional forest. had the highest overall abundance of arthropods, and densities increased in all habitats from the wet to dry season. For branch clipping collections, late successional forest had more arthropods than mid successional forest, but arthropod levels did not vary by season in any habitat. Spiders were the most abundant order sampled by both methods. Both migrant species foraged predominantly on foliage in all habitats. Their foraging height overlapped with our sampling heights in early successional forest, but sometimes exceeded sampling heights in older seral stages. Highest foraging attack rates in the wet season were observed in late successional forest, coinciding with highest sweepnet arthropod levels. In the dry season no clear pattern between foraging attack rates and potential prey levels was found. In contrast to expectations, these results suggest that overwintering migratory insectivorous birds in the Yucatan Peninsula may not face food declines during the non-breeding season. However, food availability may be adversely affected by the ongoing loss of late successional forest in the region.