Protecting egg prey from Carrion Crows: The potential of aversive conditioning
Cox R., Baker SE., MacDonald DW., Berdoy M.
Carrion Crows, Corvus corone, are held responsible for taking the eggs and chicks of many bird species. In areas of conservation significance, intervention may be required. Traditionally, managers have attempted to control predation by killing predators, but this may not be the most effective or desirable approach. A non-lethal alternative, which might protect vulnerable eggs from damage by corvids, is conditioned taste aversion (CTA), a process in which animals learn to avoid certain foods following consumption of a toxin. CTA evolved to reduce the likelihood of poisoning but may be induced deliberately using an emetic. In this study, we attempted to train wild-caught Carrion Crows to avoid eggs of a preferred colour, using three different doses of the emetic Carbachol. During pre-conditioning, we established each crow's preferred egg colour (subsequently known as 'toxic'). During conditioning, each bird was allowed access to a single Carbachol-treated 'toxic' egg for 4 h per day. We compared pre- and post-conditioning responses to untreated eggs of 'toxic' and 'non-toxic' colour. Crows took longer to attack untreated eggs after conditioning with Carbachol (all doses combined). This was the result of a reduction in attacks on 'toxic' eggs after 2 h, while there was no change in attacks on 'non-toxic' eggs. The total number of eggs attacked after 4 h did not change following conditioning, however the amount of egg consumed increased. This resulted from an increase in the number of 'non-toxic' eggs attacked and consumed. There was no change in the attack or consumption of 'toxic' eggs. The highest Carbachol dose tested (381 mg kg-1body weight) created aversions as described above for the combined results. We have shown that Carbachol can be used to manipulate crow predation on eggs in captivity. Future work should focus on captive and field trials based on a dose of 381 mg kg-1body weight. CTA could provide a more effective and more desirable alternative to culling for controlling predation by corvids on eggs of conservation significance. Such techniques might have widespread application to predation situations across a range of animal species worldwide. © 2004 Elsevier B.V. All rights reserved.