Opportunistic predation reveals a hidden cost of fighting in birds

Abstract

Predation risk is often hypothesized to be a cost of escalated fighting, and it relies on the assumption that predators eavesdrop on distracted prey. However, there is no direct evidence supporting these two ideas. Here, I report a predation event that occurred immediately after escalated fighting in birds. Two Rufous Horneros (Furnarius rufus) were engaged in a contest on the ground, while a third hornero watched from a close by (~ 3 m) perch. The hornero that won the contest, having strongly pecked its opponent, then joined the third hornero on the perch. The loser hornero appeared to be injured or fatigued after fighting and crouched motionless, wings down, and belly touching the ground. Approximately 10 s after the fight, a large Aplomado Falcon (Falco femoralis) suddenly flew toward the loser hornero, caught the bird, and flew away. This casual predation record indicates the falcon was eavesdropping on these horneros’ contest, possibly using the opportunity to attack the loser hornero which, due to being injured or fatigued after the contest, was more vulnerable to predation. This anecdotal evidence indicates the existence of a predation cost associated with escalated fighting, stressing the importance of natural history records in animal behavior research.