Thursday, May 31, 2007
Why the tiny hummingbird has to work so hard for a living
Darting hither and thither, beating their wings up to 78 times a second, hummingbirds live life at fever pitch. Weight for weight, they have the greatest energy output of any warm-blooded animal. The burn up so much energy partly because their small size demands a hectic lifestyle. The smaller an animal, the greater surface area it exposes for each gram it weighs. Hummingbirds are found only in the Americas, where there are some 320 different species. With their tiny bodies - most are only 60 to 130 mm long - hummingbirds have exceedingly little mas for producing heat to make up the loss from their relatively large surface area. They therefore require a great deal of fuel to maintain their high rate of metabolism, a normal body temperature of 39 degree to 42 degree C (102 degree to 108 degree F) and a heartbeat rate of about 500 per minute while resting and up to 1000 or more per minute when very active.
The energy for this comes partly from eating insects but chiefly from the high-calorie nectar of flowers. A hummingbird generally needs to eat over half its weight in food every day. If we had to expend the equivalent amount of energy, we would have to consume 60 kg (130 lb) of bread or 170 kg (370 lb) of boiled potatoes every day to obtain sufficient calories.
To save energy during cool weather, hummingbirds may become torpid, falling into a deep sleep for several hours, their body temperature dropping to within a few degree of the air temperature. At 15 degree C (60 degree F), the slumbering hummingbird may consume as little as one-fiftieth of the fuel it uses when active.