Multi-Species Territoriality in Neotropical Foraging Flocks

Abstract

Multi-species flocking behavior in birds assumes a wide range of forms. At one extreme are casual feeding aggregations such as those of herons and seabirds (Sealy 1973, Baltz 1977, Kushlan 1977). Showing somewhat more social and temporal cohesiveness are the restless flocks of blackbirds or sandpipers that form and dissolve on a daily basis (Recher 1966, Recher and Recher 1969, Goss-Custard 1970, Page and Whitacre 1975, Burtt and Giltz 1977). Winter foraging groups of chickadees (Parus sp.) and their consorts represent a further step towards continuity and organization (Morse 1970, Austin and Smith 1972, Glase 1973, Smith 1976, Hogstad 1978). These flocks form daily during the non-breeding season and may include many of the same individuals. Tropical mixed-species foraging flocks are even more constant, existing virtually year-round (Winterbottom

Bird mixed-flocks and nuclear species in a tecoma savanna in the Pantanal

“…In fact, feeding benefits are expected if insects are flushed by flock mates or due to copying behavior (Powell, 1985). In either case, a species would require the presence and close proximity of another species that employed a specific kind of foraging behavior (Krebs, 1973;Munn and Terborgh, 1979). Although the analysis on specific association between foraging species was beyond the scope of this study, during the observations on foraging tactics, no interaction suggested that a species foraged focusing another one, which might provide increased chances of prey capture.…”

“…Most other mixed flock members foraged solitarily, silently and closely focusing the vegetation. Apparently, this pattern of foraging behavior, at least, reduces the perception of flock partners, and predators as well (Munn and Terborgh, 1979;Sullivan, 1984a,b;Ragusa-Netto, 2002). One potential benefit associated with flock foraging is that an individual within a group may discover and use widely scattered, patchily distributed food more efficiently than if it had foraged independently.…”

“…On the other hand, those species whose effect on flock cohesion is reduced or none have been classed as satellite (Powell, 1985;Dolby and Grubb, 1999;Ragusa-Netto, 2002). Among the major traits of nuclear species are: high occurrence and permanency in flocks (Powell, 1979;Hutto, 1994;Alves and Cavalcanti, 1996); enhanced sociality (Moynihan, 1962;Munn and Terborgh, 1979;Powell, 1985); conspicuous movements (Powell, 1985;Hutto, 1994); regularity of contact calls (Moynihan, 1962;Austin and Smith, 1972;Greig-Smith, 1978;Powell, 1985); front position during flock displacement (GreigSmith, 1978;Munn and Terborgh, 1979;Ragusa-Netto, 2002); enhanced perception of raptors (Munn and Terborgh, 1979;Ragusa-Netto, 2002); and reduced aggressive behavior (Powell, 1985;Hutto, 1994). In some mixed flocks more than one species may contribute to flock cohesion (Rand, 1954;Hutto, 1994).…”

“…Satellite species are less conspicuous, tend to be silent, forage alone or in pairs, usually closely focusing the vegetation (Munn and Terborgh, 1979;Powell, 1985;Hutto, 1994). Potentially, they are more vulnerable to predators, hence are likely to exploit nuclear species alertness and communication (Sullivan, 1984a,b;Hogstad, 1988;Ragusa-Netto, 2002).…”

“…Bird mixed flocks have been widely studied in the Neotropics, mainly in tall rain forests where they are richest in species (Powell, 1979;Munn and Terborgh, 1979;Stotz, 1993;Thiollay and Jullien, 1998). Mixed flocks from this area may occur either in the canopy or in the understory, and often include one nuclear and several satellite species, which are often represented by one or a pair of individuals (see reviews : Powell, 1985;Hutto, 1994).…”