Conspecific individual recognition between starlings after toxicant-induced sickness

After feeding in the presence of a cagemate (Group S, n = 16), food-deprived starlings were intubated with the toxicant methiocarb (Group E, n = 8) or its nontoxic carrier, propylene glycol (Group C, n = 8). During the 4 days after intubation, the birds in Groups E and C were presented on 2 days with the Group S bird that was present during gavage (S+ bird) and on the other 2 days with another Group S bird (S? bird). Group E (but not Group C) birds were more agonistic toward S+ birds than S? birds, fed less in their presence, and were less likely to enter and perch in the same cage quadrant with them. A second experiment suggested that such differential behavior was probably not the result of behaviors exhibited by the S+ birds. Few calls were recorded in either experiment. Although acoustic signals might have been involved, we suggest that the starlings might have used visual cues to recognize individual conspecifics that were present during aversion learning.