Can foraging birds assess predation risk by scent?

Olfaction is commonly used by a variety of aquatic and terrestrial taxa to assess predation risk. However, with a few exceptions (e.g. procellariformes and New World vultures), the evidence for the ecological relevance of olfaction in birds is sparse and inconsistent. This is the case even though birds retain the proper anatomical and neurological structures needed to use olfaction. Here, we examined whether a passerine bird responds to the chemical scent of predators in the laboratory. We exposed house finches, Carpodacus mexicanus, to the olfactory cues of predatory and nonpredatory mammalian faeces and observed their behavioural response while feeding. Finches responded to both predator and nonpredator faecal cues, but they responded to the predator cues more strongly in some analyses. For example, in response to both faecal treatments, finches delayed their first feeding, spent less time on the feeder as a whole and reduced feeding bout length; the bout length effect was particularly pronounced in the predator treatment. Vigilance did not increase but instead decreased during the faecal treatments, which may have reflected a strategy of minimizing time on the feeder (where the cue was presented). The behavioural effects of faecal cues weakened quickly over time and were most evident during the first 5 min of an observational session. Overall, our results show that finches can detect mammalian faecal cues and associate such cues with possible danger.