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Naturespeak

Hummingbirds and the anti-Atkins Diet

Whistler Naturalists

As discussed in a recent Naturespeak, the Sea-to Sky corridor is the summer home to three species of hummingbird. The most common is the Rufous hummingbird (Selasphorus rufus). Much rarer are the Calliope hummingbird (Stellula calliope) and the Anna's hummingbird (Calypte anna).

The elliptical migration paths of these three hummingbirds species take advantage of seasonally available flowers. The spring migration from their wintering grounds in Mexico and/or southern California begins in early February and follows the west coast, while the autumn migration occurs along the interior Rocky Mountains.

Flying consumes a great deal of a hummingbird's energy. Their wings beat between 20 and 200 times per second. Normal flight speed is about 45 km/h. Hummingbirds have, in relation to their size, the largest breast muscles of all birds at 30 per cent of their total weight and allows for an upstroke that provides as much power as their downstroke. To power their flight the hummingbird has a heart rate of up to 1,260 beats per minute. In comparison the human heart beats about 72 times per minute.

Once they arrive at their winter and summer grounds as well as stops along their migratory route, hummingbirds select and protect a territory. Territory sizes vary, with each individual hummingbird seeming to know just how many flowers it will need to forage to get enough food. If the area is abundant with flowers the territory will be small, but if the flowers are few and far between the territory will be much larger. In fact, in one study, after scientists put a blanket over some of the flowers in a hummingbird’s territory, the bird expanded its territory to compensate.

Other studies have indicated that hummingbirds will exploit the flowers along the periphery of its territory at dawn and dusk, in order to deplete the nectar most accessible to competitors throughout the day.

Hummingbirds have been described as adamant, aggressive and feisty protectors of their territory. They will wage war on all invaders of their territory whether they be insects, other bird species or other members of their own species, male or female. They intercept these intruders with air attacks using their bills and claws, as well as angry buzzing vocalizations.

A hummingbird’s adamant selection and protection of its territory can be explained by the fact that they must consume at least half of their total weight in food and twice their weight in water per day. This is required due to their small size and the energy they expend in flight, feeding growth, reproduction as well as maintaining their warm-blooded body temperature.

Despite these immense levels of required consumption, hummingbirds do not feed constantly. They make approximately 14-18, 45-second foraging bouts per hour. For the remainder of the time a hummingbird will perch and oversee its territory for invaders.

Studies have indicated that the reason hummingbirds spend 10-15 minutes of every hour foraging is that they need the rest of the time for digestion. The average transit time of nectar through a hummingbird’s digestive system is one hour, during which 97 per cent of the sugars are extracted, to be used for energy requirements.

In comparison the human digestive system extracts 50 per cent of the sugars from most carbohydrates. For the other 45-50 minutes the hummingbird is emptying its crop. A "crop" is a specially modified part of the digestive system that stores food immediately after it is taken in. We do not have these.

The hummingbird must wait until its crop is half empty, which takes about 4 minutes, before foraging again. Thus, they forage only as often as required to maintain the rate at which the crop passes nectar into the rest of the digestive system. In the meantime, the hummingbird conserves energy by remaining immobile, as flying require eight times as much energy.

Besides its high carb diet the hummingbird does need some protein and fat and gets these by feeding on pollen and the small insects that it finds in flight or on flowers.

In addition to spending the majority of their daylight hours sedentary, hummingbirds become torpid at night to conserve energy. "Torpid" means they let their body temperature; the temperature is regulated at a level similar to the surrounding air of their local environment. Their normal body temperature is approximately 40°C but it can drop to 20°C. The decrease in body temperature results in a reduction in their metabolism. Thus, at its normal body temperature a hummingbird could lose 10 per cent of its body weight per night, while a torpid state this results in only a 1 per cent loss.

Hummingbirds, tiny marvels that they are, are a prime example of how a high carb, sedentary and even at times torpid lifestyle can be essential for survival in some animals.

Thanks for all those who contacted me with their early season hummingbird sightings, though no one was able to beat Bobbi Sandkul of Pinecrest Estates and her sighting of March 27th. Once again, for help identifying our local hummingbirds go to: http://www.mangoverde.com/birdsound/fam/fam86.html .

Upcoming Events:

Monthly Bird Walk — The next bird walk will take place Saturday, May 1st. Join Whistler experts in the monthly update of our feathered locals and migrants. For details, contact Michael Thompson: 604-932-5010.

Calling all Aspiring Nature Writers and Photographers — Have an interest in natural history? Want to educate others about your favourite flora and/or fauna? Write your very own Naturespeak article or send us your photos to accompany our articles. For more information contact Sorcha Masterson at 604-932-5089 or e-mail: sorc_m@hotmail.com




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