EFFECTIVENESS, BIASES AND MORTALITY IN THE USE OF APOMORPHINE FOR DETERMINING THE DIET OF GRANIVOROUS PASSERINES

We analyze the effectiveness, biases and Limitations of a poorly-known emetic, apomorphine, for studying the diet of granivorous birds. Apom orphine was tested on three Fringillids yielding an effectiveness of 4 3-78%, comparable to that reported for the most common emetic, tartar. The effectiveness of the emetic varied significantly among species, p robably due to different physiological tolerances. Older chicks and ad ults were equally sensitive to apomorphine, but it was ineffective in young chicks. The action of the chemical was not independent of food t ype, and certain food items were underrepresented with this method. Ho wever, the importance of most food categories closely resembled the on e found through dissection. Mortality caused by exposure to apomorphin e was low (< 3%) and successive applications of apomorphine proved to be innocuous, thus allowing for long term studies. Yet, the effectiven ess of apomorphine decreased when administered repeatedly within a sho rt time. Apomorphine is an advisable tool for laboratory and held work on granivorous passerines because it is effective, practically harmle ss, provides reliable results, and can be used repeatedly and easily b oth with nestlings and adults.