Mixed species flocks of insectivorous birds are a common feature of the understory in amazonian rainforests. The groups often follow a "leader" species, whose frequent vocalizations are thought to communicate information about movement and predator threats. Other species, like the Black-faced Antbird, join flocks when possible. Since the flock territories are 2-4 times larger than antbird territories, antbirds cannot permanently join the flocks.
Antbird calls are very similar to antshrike (flock leader) calls, and antbirds may use the similarity to confuse flock species into responding. This would allow antbirds to easily find flock species in the dense rainforest understory. To test this hypothesis, we used two methods. First, we compared the calls of antbirds whose range overlaps with antshrikes to populations of antbirds whose range does not overlap with antshrikes. Second, we performed a playback experiment where we directly tested the behavioral response of flock species to the mimic call of Black-faced Antbirds. Figure 1 The flock leader (top left) produces vocalizations that several species follow. The Black-faced Antbird (Male, female, bottom) generates mimetic vocalizations that the flock responds to. We evaluate the mimetic call over large geographic areas.
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The results of our playback experiments further support the hypothesis. Antbird calls resulted in behavioral response from both flock leading antshrikes and other flocking birds. These behavioral responses were similar to antshrike responses to their own species. This suggests the call is confused by both flock leaders and flocking species, allowing antbirds to generate responses from them in order to easily locate and join flocks.
Figure 3. Flock leading antshrikes responded similarly to their own species calls and the mimetic antbird calls (graph: mimic, leader). The flock leading antshrikes did not respond to the song of antbirds or to controls (graph: mimic control, forest control).
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