Thursday, August 25, 2011

Tiny Titans: Hummingbirds

Juvenile and female hummingbirds can have remarkably similar plumage, making identification very difficult. Image by Keith Bauer.

There’s something mesmerizing about watching them buzz around a feeder, a seemingly endless line of thirsty beaks. Have you ever tried to count how many hummingbirds actually visit your feeders at one time? Some folks I know maintain 10 or more feeders, going through 50 pounds of sugar a week! A friend stopped by today to drop off one of his fabulous hummie images and professed to know, not the total number that visit his feeder, but the number Rufous Hummingbirds present at his feeders. Two! There’s only room for one little red devil at each feeder – they drive off all others. We all watch them; and many of us feed them. These tiny titans are found only in the Western Hemisphere. They might look tiny and fragile, but hummies are anything but. They pack some amazing adaptations suited to their diminutive lifestyle.

They weigh in between 2 and 20 grams, depending on the species, about three cents worth, or the weight of 3 U.S. penny coins at 3 grams each. The world’s smallest living bird is the Bee Hummingbird, native to Cuba, at 1.8 grams (0.063 oz) and 2 inches in length. Our most common nesting hummingbird is the Black-chinned that weighs 9 grams. The slightly larger Broad-tailed Hummingbirds dominate at higher elevations. And, Rufous and Calliope Hummingbirds arrive in July on their way south. For me, the Fourth of July weekend, is filled with anticipation as I wait and watch my Jemez mountain feeders for the little red hummer that always seems to appear just then.

Hummingbirds can fly vertically in order to capture fluid in pendulant flowers, like this juvenile Rufous Hummingbird. Image by David Powell.

Hummingbirds got their name because their wings beat so fast that they make a humming sound, similar to that of a bee’s buzz. They can fly forward, backward, rise vertically, and hover. In order to understand how this type of flight is possible, consider that their wings move in a figure 8 motion with about 50-80 wing beats per second. At the same time their tiny heart races too, ranging from 250 beats per minute while at rest to 1,250 beats per minute in flight. Hummingbirds can reach speeds of up to 60 miles per hour.

With such a high octane lifestyle, hummingbirds require disproportionate quantities of nectar or sugar water to fuel their high-energy life style, as much as 90% of their diet. Their elevated metabolism requires an enormous food intake, typically more than one and one-half times the bird's weight in nectar alone each day. Flowers provide their food naturally, but when temperatures plummet, these sources dry up or disappear. Then, artificial sugar water feeders become critically important to survival.

The diminutive Calliope Hummingbird is the smallest North American species. Image by David Powell.

Hummers eat small insects, spiders, ants, and caterpillars, and even poach trapped insects from spider webs. When you see them hovering in mid-air or zipping to and from a perch they are almost certainly picking off flying insects. Although, high-calorie nectar or sugar water is the dominant part of their diet, protein-rich insects are also important, which also is affected by unexpected temperature drops.

Some hummingbirds are quite confiding when around humans, seemingly oblivious to our presence. Image by David Powell.

Most North American hummingbirds avoid cold weather extremes by migrating to Mexico or further south. However, many hummingbirds, remain year-round in the southern U.S. , in places like California and Arizona. Increasingly, some hummingbirds that typically migrate to Mexico, such as Rufous Hummingbirds, are wintering in the southeastern U.S. , trading a southerly migration for an eastward journey. Parts of the southeast are seeing increasingly large populations of our western species during the winter months.

They migrate in response to hormonal changes, which are triggered by decreasing daylight hours. Nothing you can do will make them stay too long, so it's not necessary to stop feeding them to force them to go south. On the contrary, they need to fatten up to nearly double normal body weight to survive the journey, and appreciate your feeder more than ever up until literally the last minute before they depart. The standard recommendation now is to keep feeders in place and until two weeks after the last hummingbird sighting.

The Black-chinned Hummingbird is the most common nesting bird in the Middle Rio Grande Bosque. Image by David Powell.

When late-departing migrants are surprised by cold weather, or when abnormal freezes affect resident hummingbirds, intervention by well intentioned people with back yard feeders can be life-saving. Hummingbirds survive the night by ingesting copious amounts of nectar at dusk, storing this reserve in their crops and digesting it throughout the night, during sleep. In cold conditions, hummingbirds drop into a hibernation-like state (torpor) which conserves energy through reduced heart rate, breathing and temperature, but which also increases the birds' risk to predation. You can help hummingbirds during these extremes by providing plenty of sugar water, and by insuring that the syrup remains unfrozen.

Sugar water in feeders will remain liquid at 32 degrees Fahrenheit, the temperature where plain water freezes, but if temperatures drop much below this level, even sugar water will freeze. Higher concentrations of sugar to water lower the freezing point, but become difficult for hummingbirds to ingest, and are not recommended. Monitor your feeders closely. If temperatures are forecast to fall below freezing overnight, bring your feeders indoors after dark, after birds have quit feeding, and then re-hang them at the earliest light, before hummingbirds begin feeding.

Increasing numbers of Rufous Hummingbirds and other species now are wintering in the southeastern U.S. in an easterly rather than southerly migration. Might that be fueled by the presence of feeders? Image by David Powell.

In early February 2011, much of the U.S. was hit by arctic air. In southeastern Arizona, where Costa's and Anna's Hummingbirds are common throughout the winter, early morning temperatures dropped to the mid-teens and below, impacting insects and flowers. Artificial feeders became critical to hummingbird survival, and even these would freeze solid if unattended. Fortunately, bird lovers across the area stepped up and kept feeders filled and thawed. Freezing weather is unavoidable, but when it comes, a little effort on our part will make a world of difference to our hummingbirds.

Hummingbird populations appear to be positively affected by our penchant for watching them at our feeders. Let’s give them a helping hand this fall, by keeping our feeders cleaned and filled until all have had a chance to move south.

No comments: