Once bitten twice shy: long‐term behavioural changes caused by trapping experience in willow warblers Phylloscopus trochilus

In dangerous situations, animals learn from experience to anticipate risks during similar subsequent occasions. Mist netting may represent just such a dangerous occasion and may serve as a tool to get insight into whether and how memorizing and recognition of the circumstances that form the prelude to a recapture can alter the animal's behaviour after capture, as well as it may affect the subsequent recapture rates. We used a playback lure to study the capture latency in willow warblers Phylloscopus trochilus, both without any and with a previous capture experience (either in the same year or in a previous one). We found increased response latencies to the playback lure for experienced males, compared to naive males. Naive males responded faster in the presence of a mist net than without a mist net; while experienced males tended to increase their response latencies. Individuals with between‐year capture experience showed exactly the same response pattern as individuals with a capture experience within the same year. These findings suggest that the birds may recall the capture event even a year later. It is very likely that the playback lure, with or without the net's presence, contributed significantly to the apparent risk of detection. We believe our study reveals that long‐lasting modifications of behaviour induced by capture and handling deserve further attention, as they might have a serious impact on the value of behavioural and ecological data, which is either based upon observing captured individuals and/or upon the recapture rates.