Pellets recovered from stick nests and new diet items of Furnariidae (Aves: Passeriformes)

This is the first record showing eleven species in seven genera of Furnariidae (Aves: Passeriformes) from Argentina that regurgitate pellets. A total of 627 nests of Furnariidae was examined, and from 84 nests (13.3%), 1,329 pellets were recovered. These pellets were found in the closed, domed nests of many Furnariidae, because in comparison to other passerine birds, their nests were used for roosting, especially in the subfamily Synallaxinae. Anumbius annumbi had the highest percentage of nests containing pellets. Food items identified from the pellets provided important new data on the diets of several species of Furnariidae.Fil: Turienzo, Paola Noemí. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Di Iorio, Osvaldo Rubén. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Biodiversidad y Biología Experimental; Argentin

Costs of behavioral synchrony as a potential driver behind size-assorted grouping

Group-living animals must synchronize their behavior to maintain group cohesion. Synchrony is best maintained by individuals similar in size because they have similar activity budgets and thus can easily coordinate their behavior, which minimizes potential trade-offs. Many groups assort by size, presumably to reduce predation risk and foraging competition. However, because groups can only be maintained by individuals that synchronize their behavior, we propose that maintenance of synchrony may also be an important factor contributing to size-assorted grouping. Similar-sized individuals should maintain synchrony through similar swimming speeds, similar foraging activity and through cohesiveness with the group, and, therefore, pay the least costs of group-living: body mass should increase over time. However, odd-sized fishes may have to adjust their foraging activities and thus lose body mass because of the need of synchrony. We measured the aforementioned variables using varying sizes (large and small) and colors (red and wild-type) of heterogeneous (1 odd focal fish among 5 similar fishes) and homogeneous (6 similar fishes) groups of zebra fishes. Groups composed of similar-sized individuals had the highest degree of synchrony--small fishes gained mass, whereas large fishes grew very little or not at all. Groups composed of different-sized individuals, although able to maintain synchrony most of the time, did so at significantly lower levels than similar-sized fishes--odd small fishes in these groups gained significantly less mass, whereas odd large fishes did not. We show that synchrony in behavior is costly and that these costs may contribute, in part, to group choice. Copyright 2011, Oxford University Press.