Life In the Laid Back Lane

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Anyone who has spent much time somewhere south of the Tropic of Cancer down to the Tropic of Capricorn knows that things move a little slower in the tropics, mon. The mystique of the slower life style is part of what draws so many people to the Tropics each year.

Now, through the research described below we have evidence that even tropical birds have adapted to a slower life style in the laid back lane, mon. Enjoy!

PNAS | May 29, 2007 | vol. 104 | no. 22 | 9340-9345
Tropical birds have a slow pace of life

Popko Wiersma, Agustí Muñoz-Garcia, Amy Walker, and Joseph B.
Williams

Tropical birds are relatively long-lived and produce few offspring,which develop slowly and mature relatively late in life, the slow end of the life-history axis, whereas temperate birds lie at the opposite end of this continuum. We tested the hypothesis that tropical birds have evolved a reduced basal metabolic rate (BMR). We measured BMR of 69 species of tropical birds, the largest data set amassed on metabolic rates of tropical birds, and compared these measurements with 59 estimates of BMR for temperate birds. Our analyses included conventional least squares regression, regressions based on phylogenetic independent contrasts, and a comparison of BMR of 13 phylogenetically matched pairs, one species from the tropics and one from northerly temperate areas. Our triptych showed that tropical birds had a reduced BMR, compelling evidence for a connection between the life history of tropical birds and a slow pace of life. Further, tropical migrants breeding in temperate habitats had a lower BMR than did temperate residents, suggesting that these migrants have physiological traits consistent with a slow pace of life. In addition, we determined that tropical birds had a lower cold-induced peak metabolic rate and thermogenic metabolic scope than temperate species, a finding that is consistent with the hypothesis that their environment has not selected for high levels of thermogenesis, or alternatively, that a slow pace of life may be incompatible with high thermogenic capacity. We conclude that physiological function correlates with the suite of life-history traits.