Why do adult dogs 'play'?

Among the Carnivora, play behaviour is usually made up of motor patterns characteristic of predatory, agonistic and courtship behaviour. Domestic dogs are unusual in that play is routinely performed by adults, both socially, with conspecifics and with humans, and also asocially, with objects. This enhanced playfulness is commonly thought to be a side effect of paedomorphosis, the perpetuation of juvenile traits into adulthood, but here we suggest that the functions of the different types of play are sufficiently distinct that they are unlikely to have arisen through a single evolutionary mechanism. Solitary play with objects appears to be derived from predatory behaviour: preferred toys are those that can be dismembered, and a complex habituation-like feedback system inhibits play with objects that are resistant to alteration. Intraspecific social play is structurally different from interspecific play and may therefore be motivationally distinct and serve different goals; for example, dogs often compete over objects when playing with other dogs, but are usually more cooperative when the play partner is human. The majority of dogs do not seem to regard competitive games played with a human partner as "dominance" contests: rather, winning possession of objects during games appears to be simply rewarding. Play may be an important factor in sociality, since dogs are capable of extracting social information not only from games in which they participate, but also from games that they observe between third parties. We suggest that the domestic dog's characteristic playfulness in social contexts is an adaptive trait, selected during domestication to facilitate both training for specific purposes, and the formation of emotionally-based bonds between dog and owner. Play frequency and form may therefore be an indicator of the quality of dog-owner relationships.

The effect of familiarity on behavior of kenneled dogs during interactions with conspecifics.

Kenneled environments often prevent direct physical contact between dogs, potentially causing stress, and so it has been recommended that such contact should be provided. This study examined the effect of familiarity on the behavior of dogs during off-lead interaction. Kenneled dogs (3 breeds) were given 15-min off-lead interactions with a familiar dog and an unfamiliar dog; the behavior of the focal dog and the distance between the dogs were recorded. More time in contact and interaction behaviors were recorded at 0 to 3 min with unfamiliar dogs than with familiar dogs. At 9 to 12 min, familiar pairs spent more time within 5 body lengths and more time being followed than unfamiliar pairs, who spent more time at more than 5 body lengths apart. This suggests that the initial interaction is more important when dogs are unfamiliar, but once this "greeting" has occurred, unfamiliar pairs are more likely to investigate their surroundings independently rather than together. Breed differences were observed only at 0 to 3 min. The study suggests that familiarity should be taken into account when assessing the effectiveness of conspecific contact as a potential enrichment for kennel-housed dogs.

Habituation and dishabituation during object play in kennel-housed dogs.

Domestic dogs are reported to show intense but transient neophilia towards novel objects. Here, we examine habituation and dishabituation to manipulable objects by kennel-housed dogs. Labrador retrievers (N = 16) were repeatedly presented with one toy for successive 30-s periods until interaction ceased. At this point (habituation), a different toy was presented that contrasted with the first in both colour and odour (since the dog's saliva would have accumulated on the first), colour alone, or odour alone. No effect of the type of contrast was detected in the number of presentations to habituation, the difference in duration of interaction between the first presentation of the first toy and the presentation of the second toy (recovery), or the duration of interaction with the second toy (dishabituation). Varying the time interval between successive presentations of the first toy up to habituation between 10 s and 10 min had no effect on the number of presentations to habituation, nor did it alter the extent of dishabituation. Varying the delay from habituation to presentation of the second toy, between 10 s and 15 min, affected neither the recovery nor the dishabituation. Overall, the study indicates that loss of interest in the object during object-orientated play in this species is due to habituation to the overall stimulus properties of the toy rather than to any single sensory modality and is also atypical in its insensitivity to the interval between presentations.