Most dog and cat owners will happily describe their pet's disposition down to the smallest, human-like detail. But how much of that is over-reaching anthropomorphizing and how much is an individual animal's actual "personality" shining through?

Researchers in the U.K. devised a series of tests to see how individual animals respond—both behaviorally and biologically—to different situations, choosing as their subjects 22 captive greenfinches (Carduelis chloris).

Test 1: Who's scared of a cookie cutter? Each hungry greenfinch must face a small brightly colored cookie cutter in their food bowl. Some brave birds disregarded the novel intrusion and dived right into their feed within seconds. Other finches tarried for more than half an hour without working up the courage to eat from the adorned dish.

Test 2: What's so interesting about Q-tips? With no food or water in the cage to distract the birds, a bundle of white Q-tips, tied together with string, is placed near one of four perches. Most birds declined to touch the new object, but some curious birds did flit to the nearby perch for a closer look.

Test 3: How stressed are you, really? A behavioral reaction to a new situation only tells part of the story. To hunt for the physiologic response during these actions, the researchers screened the birds for their oxidative profiles, a blood-based measure of metabolites that can boost energy but can ultimately hamper cell repair.

The researchers found that fear of the cookie cutter and curiosity about the cotton swabs "were consistent within individuals across days, and thus constitute personality traits in the greenfinch." And "both traits were related to oxidative profile." The most cautious birds had the highest levels of oxidative stress, and those that were most curious had better protection from the metabolite damage. The team cautioned, however, that "not all personality traits may be linked to hormonal stress responsiveness."

Personality research in animals is not new. Certainly other apes show indications of having nuanced individual personalities, and some researchers have even proposed personalities for invertebrates such as octopuses.

Rather than trying to pigeonhole Polly as an introvert or extrovert, the researchers hope to use these findings to look for larger implications about how these individual variances might affect survival in the wild.

"Neophobic birds—those that are afraid of new things—may suffer high costs of oxidative stress and die early," Kathryn Arnold, of the Environment Department at the University of York and co-author of the new study, said in a prepared statement. Being chary, however, promises some immediate benefits, she noted. These birds "might also be less likely to be eaten by a predatory because they are more wary than bolder birds."

The results of the study appear in the May issue of The Journal of Experimental Biology.

Image courtesy of Kathryn Arnold