We tested the idea that bird odour placed as ‘chemical camouflage’ around bird breeding areas can protect vulnerable eggs and chicks by reducing the hunting success of mammalian predators (Price and Banks 2012). Before birds settled in areas to breed, we randomly deployed readily-available generic bird odours, such as chicken or quail, in the environment at two 1,000 ha riverbed sites in the Mackenzie Basin of New Zealand’s South Island. Predators (cats, mustelids, hedgehogs) investigated the odours but received no food rewards. After several weeks, predators’ interest in investigating the odour waned. Presumably we deceived them into thinking that bird odours were not a profitable cue, thereby reducing predation pressure when birds began nesting. We anticipated that some predators would ‘re-learn’ that bird odour sometimes results in a reward, so additional use of generic bird odour during the nesting period reinforced for predators that bird odour was not always associated with food, and also created a confusing surfeit of real and similar bird odour. This camouflage technique may give birds enough time to breed successfully before predator learning resumes. We report preliminary results from laboratory and field trials that test whether predators ‘generalise’ bird odour cues sufficiently to modify hunting behaviour and, therefore, whether generic odours resulted in increased nest survival of threatened shorebird species.
Price, C.J. and Banks, P.B. (2012). Exploiting olfactory learning in alien rats to protect birds' eggs. Proceedings of the National Academy of Sciences of the United States of America 109, 19304-19309.