Hear that sound? It's a Costa's hummingbird (Ca)

[Donna]

Hummingbirds are the smallest birds encountered in the Coachella Valley.

In addition to their size, they are characterized by long, slender bills used for reaching deep into tubular flowers, incredibly rapid wing beats that produce a humming sound, and the ability to fly backward — a feat no other bird group can duplicate.

During the day, hummingbirds maintain a high metabolic rate requiring that they feed frequently. At night, however, they enter a state of torpor as their body temperature drops to that of their surroundings.

Though a number of hummingbird species are known to migrate through the North American deserts, only three — black-chinned, Anna's and Costa's — are known to breed here. Costa's hummingbird is the only species that reaches its greatest abundance in desert environments.

The male Costa's is often first noticed when performing spectacular nuptial flights beginning in February. The aerial maneuvers consist of 100-foot, U-shaped configurations accompanied by high-pitched sustained whistles. These displays are in view of a female perched nearby. Such impressive courtship behavior stands in marked contrast to the abandonment of the female after mating.

Unlike many male birds that participate in nest construction, incubation duties and feeding of young, a Costa male plays no role after fertilization. A male may mate with several females and vice versa, a breeding system appropriately termed promiscuous.

Contrary to popular belief, young hummingbirds are not reared exclusively on a diet of nectar. Insects and spiders are the most important dietary mainstay and are essential for growing young. Hummingbirds thus visit flowers not only for nectar but also for the tiny arthropods that have entered the blossom. Hummingbirds also capture insects in midair.

The most important behavioral adaptation of Costa's hummingbirds is their exodus from the desert in late May and early June. There are almost no records of this species from June through September in Joshua Tree National Park and Organ Pipe Cactus National Monument. Observations elsewhere in the desert are uncommon.

It appears many Costa's hummingbirds migrate to the chaparral of the coast ranges of California at this time as their arrival there coincides with their disappearance in the desert. Additional evidence for this hypothesis can be found in several museum collections that contain individuals with characteristics of Arizona populations but which have been collected in California during summer.

It is not surprising most individuals vacate the desert during the hot months. The small size of hummingbirds makes them especially vulnerable to overheating. They must evaporate comparatively large amounts of water, through a kind of panting, to keep cool.

It has been estimated that a 150-pound man would have to drink more than five gallons of water a day to maintain water balance if he lost water at the rate of a Costa's hummingbird.

Jim Cornett is a desert ecologist living in Palm Springs.