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Résumé :
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Flight-song displays usually include distinctive vocalizations and behaviors that are probably energetically expensive and also likely to attract the attention of aerial predators. We observed flight songs performed by Dusky Flycatchers (Empidonax oberholseri) in two breeding populations. During 15 yr at Tioga Pass, California, we observed the display twice and, during 9 yr at Steamboat Mountain, British Columbia, we observed 21 flight-song displays. These displays were generally observed later in the breeding season, suggesting that they were not used for courtship, mate attraction, or territory defense. However, for 83% of these displays, a raptor was observed to be present, usually either an American Kestrel (Falco sparverius) or a Sharp-shinned Hawk (Accipiter striatus). We hypothesize that these displays, like stotting or other pursuit-deterrent signals, may be directed at small raptors that represent a greater threat to Dusky Flycatchers and might deter attack by signaling awareness. However, because only males were observed performing flight-song displays, it is also possible that these displays serve to alert mates and offspring about the presence of an aerial predator and reduce their vulnerability to attack.
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