That dog won't fit: body size awareness in dogs.

With very few exceptions, no coherent model of representing the self exists for nonhuman species. According to our hypothesis, understanding of the Self as an object' can also be found in a wide range of animals including the dog, a fast-moving terrestrial predator/scavenger, with highly developed senses and complex cognitive capacity. We tested companion dogs in three experiments in which they faced three different variations of the same physical challenge: passing through an opening in a wall. We predicted that if dogs are capable of representing their own body size, they will react differently when faced with adequate or too small openings. We found that dogs started to move towards and approached the too small openings with significantly longer latencies than the suitable ones; and upon reaching it, they did not try to get through the too small openings. In another experiment, the medium-size (still large enough) opening was approached with latencies that fell between the latencies measured in the cases of the very large or the too small openings. Having discussed the potential underlying mechanisms, we concluded that our results convincingly assume that dogs can represent their own body size in novel contexts.

Dog growls express various contextual and affective content for human listeners.

Vocal expressions of emotions follow simple rules to encode the inner state of the caller into acoustic parameters, not just within species, but also in cross-species communication. Humans use these structural rules to attribute emotions to dog vocalizations, especially to barks, which match with their contexts. In contrast, humans were found to be unable to differentiate between playful and threatening growls, probably because single growls' aggression level was assessed based on acoustic size cues. To resolve this contradiction, we played back natural growl bouts from three social contexts (food guarding, threatening and playing) to humans, who had to rate the emotional load and guess the context of the playbacks. Listeners attributed emotions to growls according to their social contexts. Within threatening and playful contexts, bouts with shorter, slower pulsing growls and showing smaller apparent body size were rated to be less aggressive and fearful, but more playful and happy. Participants associated the correct contexts with the growls above chance. Moreover, women and participants experienced with dogs scored higher in this task. Our results indicate that dogs may communicate honestly their size and inner state in a serious contest situation, while manipulatively in more uncertain defensive and playful contexts.

Human handling might interfere with conspecific recognition in the european rabbit (Oryctolagus cuniculus).

Handled rabbit pups react with decreased fear to a human at weaning. We hypothesized that pups learn species-specific features of their handler. Experiment 1 showed that handled animals' reactions were similar to both a human and their mother. Experiment 2 showed that pups reacted similarly to their mother and other adult rabbits. In Experiment 3, we used nonhandled control pups, and pups in the experimental groups were stimulated either by a human, a cat, or both. Only human-handled animals showed high affinity to approach a human at weaning. Similarly, only rabbit pups exposed to a cat did not show fear reaction towards a cat. Nonhandled controls avoided both the cat and the human, and rabbits stimulated by both species did not avoid any of them at weaning. We demonstrated that handling affected the behavior of weanling rabbits in a selective manner, as they only approached those objects frequently to which they had been exposed to.

The effect of early handling is dependent upon the state of the rabbit (Oryctolagus cuniculus) pups around nursing.

We investigated the behavior toward humans in 4-week-old pups and adult rabbits handled daily at different times around the nursing visits during their 1st week of life. The timing of handling significantly influenced its efficiency in altering the subsequent behavior of rabbits. Animals handled around nursing readily approached a human hand when tested at weaning. Other pups, handled either 6, 12, or 18 hr after nursing, avoided the human hand. Our results show that there is a narrow sensitive period for successful stimulation, because only those rabbits that were handled within the interval starting 15 min before and ending 30 min after nursing became tame. The effect of early handling proved to be long-lasting because nonhandled rabbits tested as adults were afraid of humans and showed behavioral elements of avoidance, while the handled ones behaved fearlessly in the open field. The effect of handling proved to be specific toward humans because both handled and nonhandled animals showed avoidance toward a stuffed fox.

The ontogeny of antipredator behavior in paradise fish larvae (Macropodus opercularis) IV. The effect of exposure to siblings.

Twenty-five-day-old larval paradise fish show less avoidance behavior toward a model predator than 20-day-old fish larvae. Laboratory experiments tested two possible hypotheses: The decrease of avoidance behavior is the result of (a) change in the size ratio of larvae/model, or (b) experience with larval siblings. Larval paradise fish did not show greater avoidance of larger models or models with larger eyespots. However, if isolated for 3 days, the antipredator behavior of 25-day-old larvae became similar to younger ones. In further experiments, we raised the larvae in a larger holding tank in order to decrease the rate of encounters among conspecifics. In line with our assumptions, these larvae also showed enhanced avoidance toward a model predator. In sum, our experiments revealed that the continuous exposure to conspecific larvae was the main cause for the reduced antipredator behavior toward models. To account for our results, we suggest that larvae of nonschooling paradise fish habituate to the continuous presence of larval conspecifics and, as a result, they show decreased avoidance to the model predator. We hypothesize that this habituation process might not work in other fish species that show early schooling behavior in their development. In other words, they would not generalize the experience of conspecifics to potential predators.