Flock characteristics of ant-following birds in premontane moist forest and coffee agroecosystems

Abstract

We studied avian attendance at swarms of Eciton burchelli and Labidus praedator (Hymenoptera: Formicidae: Ecitoninae) over 5-mo periods in both 1996 and 1997, at elevations between 1400 m and 1800 m in western Panama. We conducted area searches for swarms of raiding ants and attendant birds in intact forest, traditional shade coffee habitats both adjacent to and distant from forest, and in sun coffee habitats, quantifying the size and composition of attendant flocks. All habitats except sun coffee supported numerous army ant swarms and thus a diverse assemblage of ant-following birds. A total of 411 swarming occasions attracted 126 bird species of 28 families. Of the 103 resident species, two were obligate ant-following birds, the Ruddy Woodcreeper (Dendrocincla homochroa) and the Gray-headed Tanager (Eucometris penicillata). Of the remaining species, 18 were wintering Nearctic migrants, and five were transient Nearctic migrants. Nearctic migrant species composed a greater percentage of the attendant species in shade coffee habitats as compared to forest. Several species of forest resident birds that correspond with particular foraging guilds, such as understory bark insectivores, including D. homochroa, regularly occurred in adjacent shade coffee but were never observed at swarms in distant shade coffee. Army ants may therefore be a mechanism for bringing forest birds into shade coffee, but only to a point. In western Panama, mid-elevational traditional shade coffee plantations can provide additional habitat for the diverse avifauna that attend army ant swarms. With increasing distance from large areas of continuous forest, however, the value of traditional shade coffee habitats is lessened for certain components of the bird community. Thus, protection of these habitats adjacent to intact forest should receive priority. Additionally, current transformation of coffee-growing practices, including the removal of shade trees to grow coffee in full sun, will negatively affect army ants and their associated avian followers.