Lisa J. Petit

FLOCK CHARACTERISTICS OF ANT‐FOLLOWING BIRDS IN PREMONTANE MOIST FOREST AND COFFEE AGROECOSYSTEMS

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, quan- tifying 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 spe- cies, 18 were wintering Nearctic migrants, and five were transient Nearctic migrants. Ne- arctic 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. homo- chroa, 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 pri- ority. Additionally, current transformation of coffee-growing practices, including the re- moval of shade trees to grow coffee in full sun, will negatively affect army ants and their

Modeling the flocking propensity of passerine birds in two Neotropical habitats

We examined the importance of mixed-species flock abundance, individual bird home range size, foraging height, and foraging patch characteristics in predicting the propensity for five Neotropical passerine bird species (Slaty Antwren, Myrmotherula schisticolor; Golden-crowned Warbler, Basileuterus culicivorus; Slate-throated Redstart, Myioborus miniatus; Wilson’s Warbler, Wilsonia pusilla; and Black-and-white Warbler, Mniotilta varia) to forage within flocks, rather than solitarily. We used study plots in primary mid-elevation forest and in shade coffee fields in western Panama. We expected that all species would spend as much time as possible flocking, but that the social and environmental factors listed above would limit compatibility between flock movements and individual bird movements, explaining variability in flocking propensity both within and among species. Flocking propensity was well predicted by home range size and flock abundance together, for four of the five species. While flock abundance was uniform across plots, home range sizes varied among species and plots, so that home range size appeared to be the principle factor limiting flocking propensity. Estimates of flock abundance were still required, however, for calculating flocking propensity values. Foraging height and patch characteristics slightly improved predictive ability for the remaining species, M. miniatus. In general, individual birds tended to join flocks whenever one was available inside their home range, regardless of a flock’s specific location within the home range. Flocking propensities of individual species were lower in shade coffee fields than in forests, and probably vary across landscapes with variations in habitat. This variability affects the stability and species composition of flocks, and may affect survival rates of individual species.

Fecal sac dispersal by Prothonotary Warblers: Weatherhead's hypothesis re-evaluated

Data on removal of fecal sacs by Prothonotary Warblers (Protonotaria citrea) were used to test Weatherheads (1984) hypothesis that birds carrying fecal sacs away from the nest will vary their departure directions more widely than will birds not carrying fecal sacs in order to prevent attraction of predators. We recorded the departure direction of adults and whether or not they carried fecal sacs, as well as the distance flown to drop a fecal sac. Fecal sacs dropped over land were not carried significantly farther than those dropped over water. Although the distribution of directions flown with fecal sacs was significantly different than that of directions flown without fecal sacs, Prothonotary Warblers did not vary their departure direction more when carrying fecal sacs than when not carrying sacs. In fact, the distribution of trips without fecal sacs was more varied than trips with fecal sacs. Our results contradict the results of Weatherhead (1984), possibly because of differences in data analysis, and do not support his hypothesis of fecal sac dispersal.