Dogs don't always prefer their owners and can quickly form strong preferences for certain strangers over others.

The unique relationship between dog and owner has been demonstrated in several experimental procedures, including tests in which dogs are left alone or with a stranger, tests of dogs’ appeasement or social approach when petted by their owner or a stranger, and their ability to learn when taught by their owner or a stranger. In all cases, dogs responded differently to their owner, which has been referred to as a specific attachment, and likely a product of a prolonged history of reinforcement. In the current study, we used a concurrent choice paradigm in which dogs could interact with two people, both of whom provided the same petting interaction, to test whether owned dogs would prefer their owner over a stranger and whether the familiarity of the testing context would influence preference. We also investigated whether shelter and owned dogs tested with two strangers would show a preference between strangers and whether that preference would be similar in magnitude to any preference between the owner and stranger. Owned dogs preferred to interact with their owners when in an unfamiliar context, but allocated more time to the stranger in a familiar context. Both shelter and owned dogs tested with two strangers showed a magnitude of preference for one stranger over the other similar to owned dogs’ preference for owners in an unfamiliar context. These results parallel what has been found in strange situation tests with owned dogs tested with their owners, but the strength of preference shown for one of two strangers indicates dogs can form a preference for one person quickly.