Smart, Calm Birds and Stupid, Stressed Birds

I usually glide by this sort of science news story with a shrug -- it's just one small study, trumpeting a new and strange finding, the kind of thing I assume will turn out not to be true. But this really intrigues me:

Bird species with larger than average brains have lower levels of a key stress hormone, an analysis of nearly 200 avian studies has concluded. Birds in the wild lead a stressful life. Constantly spotting predators lurking in the trees or sensing dramatic changes in temperature is essential for survival, but can leave birds on the edge of a nervous breakdown. Reading these cues triggers changes in the birds’ metabolism, particularly increases in the stress hormone corticosterone. A sharp release of the hormone within 1 to 2 minutes after a cue triggers an emergency response and prepares birds to react quickly to the threat. However, regular exposure to the dangers of the wild and, hence, to high levels of this hormone, has serious health consequences and shortens life expectancy.

Now why would smart birds make less use of stress hormones? Presumably because they use their intelligence to reason their way out of crises rather than just flying away as fast as they can. A small-brained bird whose only options are flight and fight needs that surge of stress hormones to equip its body for action, whereas a more intelligent bird might benefit more from keeping its mind clear to choose a clever ploy. Stress is hell on lifespan -- that's the main reason pets and zoo animals live longer than wild animals. So emphasizing intelligence allows the bird to adopt a life-cycle strategy emphasizing longevity and learning; the longest-lived birds are highly intelligent parrots and cockatoos, and my impression is that crows and ravens live much longer than stupid birds of similar size.

And what does this imply about human evolution? Chimpanzees live longer than monkeys, and we live longer than chimps. Could that be partly because we have emphasized intelligent problem-solving rather than the burst of fury stress hormones can give us? At some point did we cross a threshold at which our intelligence and longevity began allowing us to build up an adaptive culture that magnified our intelligence even further, reducing our need for stress hormones and therefore making us live even longer, learning even more, and so on?