Sunday, May 22, 2011

The Marvelous Hummingbird

Ever since I was a kid I have been fascinated with hummingbirds.  My grandmother used to have various tall red perenial flowers planted in front of her south and west windows.   When she was cooking or doing the dishes during the summer, she wanted to be entertained.

Hummingbirds are birds that comprise the family Trochilidae. They are among the smallest of birds, most species measuring only three to five inches long (7.5–13 cm) . These agile birds can hover in mid-air by rapidly flapping their wings 12–90 times per second (depending on the species). They are the only group of birds that can fly backwards. Their English name derives from the characteristic hum made by their rapid wing beats. They can fly at speeds exceeding 34 mph (54 km/h.

Hummingbirds use their long bills to drink nectar, a sweet liquid inside certain flowers. Like bees, they are able to assess the amount of sugar in the nectar they eat; they reject flower types that produce nectar that is less than 10% sugar and prefer those whose sugar content is stronger. Nectar is a poor source of nutrients, so hummingbirds meet their needs for protein, amino acids, vitamins, minerals, etc. by preying on insects and spiders.

The two halves of a hummingbird's bill have a pronounced overlap, with the lower half (mandible) fitting tightly inside the upper half (maxilla). When hummingbirds feed on nectar, the bill is usually only opened slightly, allowing the tongue to dart out and into the interior of flowers.

Hummingbirds drink by using protrusible grooved or trough-like tongues.They do not spend all day flying, as the energy cost would be prohibitive; the majority of their activity consists simply of sitting or perching. Hummingbirds feed in many small meals, consuming many small invertebrates and up to twelve times their own body weight in nectar each day. They spend an average of 10–15% of their time feeding and 75–80% sitting and digesting.  In the case of the male hummingbird that is dominating my feeder -- a lot of their time is spent watching for competitors and guarding the feeder.

Scientists who have studied the hummingbirds ability to fly and hover have determined that 75% of their weight is supported during the downstroke and 25% during the upstroke. Many earlier studies had assumed (implicitly or explicitly) that lift was generated equally during the two phases of the wingbeat cycle, as is the case of insects of a similar size

With the exception of insects, hummingbirds while in flight have the highest metabolism of all animals, a necessity in order to support the rapid beating of their wings. Their heart rate can reach as high as 1,260 beats per minute.  Hummingbirds are continuously hours away from starving to death, and are able to store just enough energy to survive overnight.  However, they are capable of slowing down their metabolism at night, or any other time food is not readily available. They enter a hibernation-like state during which their breathing and heart rate are both slowed dramatically (the heart rate to roughly 50–180 beats per minute), reducing the need for food.

Studies of hummingbirds' metabolisms show that they can cross the Gulf of Mexico on a nonstop flight  (500 miles or 800 km). This hummingbird, like other birds preparing to migrate, stores up fat to serve as fuel, thereby augmenting its weight by as much as 100 percent and hence increasing the bird's potential flying time.

Considering their metabolism and small size, hummingbirds can live up to a decade -- but most live three to five years.  While less than 25 different species of hummingbirds have been recorded from the United States and less than 10 from Canada and Chile each, Colombia alone has more than 160 and the comparably small Ecuador has about 130 species. 

Only the migratory Ruby-throated Hummingbird breeds in continental North America east of the Mississippi River and Great Lakes. This is the species that is dominating my front yard.

The Ruby-throated Hummingbird weighs only .016 ounces (3 grams). Adults are metallic green above and grayish white below, with near-black wings. Their bill is long, straight and very slender. The adult male has a ruby red throat patch which may appear black in some lighting, and a dark forked tail. The female has a dark rounded tail with white tips and generally either no throat patch, or a slightly lighter throat patch.

The male is smaller than the female, and has a slightly shorter beak. A molt of feathers occurs once per year, and begins during the autumn migration.

As far as is known, male hummingbirds do not take part in nesting. Most species build a cup-shaped nest on the branch of a tree or shrub. In many hummingbird species, spider silk is used to bind the nest material together and secure the structure to its support. The unique properties of silk allow the nest to expand with the growing young. Two white eggs are laid, which, despite being the smallest of all bird eggs, are in fact large relative to the hummingbird's adult size. Incubation lasts 14 to 23 days. Their mother feeds the nestlings on small arthropods and nectar by inserting her bill into the open mouth of her young and regurgitating the food into its crop.

Many of the hummingbird species have bright plumage with exotic coloration. In many species, the coloring does not come from pigmentation in the feather structure, but instead from prism-like cells within the top layers of the feathers. When light hits these cells, it is split into wavelengths that reflect to the observer in varying degrees of intensity. The hummingbird wing structure diffracts the light so that, merely by shifting position, a muted-looking bird will suddenly become fiery red or vivid green.

The Ruby-throated Hummingbird is migratory, spending most of the winter in southern Mexico, Central America as far south as South America, and the West Indies. For a small bird it migration can certainly be considered epic.

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