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Humm.. it’s a a giant!

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13.07.2005

Hummingbirds - elegant and light? Not all of them! Of approximately 340 species of hummingbirds, 70% weigh six grams or less, while 30% weigh between six and ten grams. The giant hummingbird, Patagona gigas, with its 20g, is a heavy weight! Other animal species, rodents for example, contain individuals ranging in body mass from 10 grams to a rather phenomenal 60 kilograms. However, unlike the hummingbird, these mass differences occur gradually, rather than with a large ‘gap’ of mass. Maria Jose Fernandez from University of California, Berkeley, will be presenting her work trying to unravel the secret of P. gigas’ extreme size at the SEB meeting at the Universitat Autonoma de Barcelona on Tuesday 12th of July.

The giant hummingbird can be found in countries such as Ecuador and Chile, where Fernandez is investigating the upper limit, which could explain the upper body size among hummingbirds. She measured the influence of energy use and nutrient uptake on the birds’ hovering flight style, a mechanism which is in some ways similar to that of helicopters. Hovering is highly demanding, displaying some of the highest mass specific rates of aerobic metabolism and muscle power output among vertebrates. No difference was seen between the maximum metabolic rate and the daily energy expenditure, which means that the basal metabolic rate is the influential factor for the size of the hummingbird. “It is not unreasonable to suggest that there are energetic constraints on the evolution of body size”, says Fernandez.

Diana van Gent | Source: alphagalileo
Further information: www.sebiology.org/vcsearch.asp

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