Corvid Re-Caching without ‘Theory of Mind’: A Model

Scrub jays are thought to use many tactics to protect their caches. For instance, they predominantly bury food far away from conspecifics, and if they must cache while being watched, they often re-cache their worms later, once they are in private. Two explanations have been offered for such observations, and they are intensely debated. First, the birds may reason about their competitors' mental states, with a ‘theory of mind’; alternatively, they may apply behavioral rules learned in daily life. Although this second hypothesis is cognitively simpler, it does seem to require a different, ad-hoc behavioral rule for every caching and re-caching pattern exhibited by the birds. Our new theory avoids this drawback by explaining a large variety of patterns as side-effects of stress and the resulting memory errors. Inspired by experimental data, we assume that re-caching is not motivated by a deliberate effort to safeguard specific caches from theft, but by a general desire to cache more. This desire is brought on by stress, which is determined by the presence and dominance of onlookers, and by unsuccessful recovery attempts. We study this theory in two experiments similar to those done with real birds with a kind of ‘virtual bird’, whose behavior depends on a set of basic assumptions about corvid cognition, and a well-established model of human memory. Our results show that the ‘virtual bird’ acts as the real birds did; its re-caching reflects whether it has been watched, how dominant its onlooker was, and how close to that onlooker it has cached. This happens even though it cannot attribute mental states, and it has only a single behavioral rule assumed to be previously learned. Thus, our simulations indicate that corvid re-caching can be explained without sophisticated social cognition. Given our specific predictions, our theory can easily be tested empirically

Female and male serins ( Serinus serinus ) respond differently to derived song traits

Abstract We tested if male or female behavior towards manipulated song indicates intra- or inter-sexual selection of two characteristics of serin song that are extreme and evolutionarily derived in this species: high frequency and fast syllable rate. In a first experiment, we monitored vocal responses and attendance to song playbacks. Female behavior indicated a preference for high-frequency song and suggested an aggressive function for fast syllable rates, as fast songs inhibited vocal response. Males did not show discrimination of frequency or syllable rate with this experimental design. The second experiment used a simple approach/no approach design, and in this experiment, males showed stronger discrimination between stimuli than did females. Therefore, sex differences in discrimination appear not to result from differences in perceptual abilities but from differences in the context of stimulus presentation. The second experiment also supported a role of song frequency in female choice, as the effect of frequency was limited to females: males did not respond differently to song frequency and approached high-frequency songs less than females did. Results of this experiment also supported an aggressive function for fast syllable rates, as the effect of fast songs did extend to male behavior. Taken together, our results indicate that the high frequency and fast syllable rate of serin song cannot result from a single selection process: while high frequency may have evolved by inter-sexual selection, syllable rate provokes a pattern of response that is more consistent with intra-sexual selection