Birds that mate for life can afford to take a long time to establish a relationship. In such birds, they may pair up long before they breed. Their manner of mating can be so obscure that it escapes notice. Migratory birds often only pair for one season. The male acquires a territory and then aggressively sings until he attracts a mate. The couple must find each other quickly and mate during a short period of time in order to be successful. Hummingbirds come together only long enough for eggs to be fertilized. As such, the association of the male and the female is an extremely transitory affair. The hummers’ methods for attracting mates are among the most varied and fascinating of all birds.
In the animal world as a whole, pairs are brought together by a combination of olfactory, visual and auditory signals. Birds have a poorly developed sense of smell and do not use olfactory signals at all. But they do use visual displays and vocalized songs to advertise themselves and attract the opposite sex. Among hummers, those that live in fairly open territory can rely upon the swinging U-shaped displays common to our North American species. Only the Anna’s hummingbird is known for its song in North America. But in South America the hummers live amidst heavy tropical vegetation. Aerial flight displays only work well at close range. Many South American hummers use song in breeding displays. Being small birds, their song does not carry for long distances. The males have overcome this liability by forming groups of male birds that come together in one spot for collective singing. These groups are called leks, or singing assemblies. They occur in the same spot year after year, being abandoned only if the habitat changes. By increasing the volume of the song with group singing and doing it in the same location year after year, the males increase their success in finding females. There are often long distances that are void of hummers between the leks.
The makeup of leks varies from species to species. The number of hummingbirds in a lek may vary from two to one hundred or more. The placement of a lek may be down low in dense undergrowth. The hermit hummingbirds perch on twigs only a yard of so off the ground. Their brown colors blend in with the vegetation. The more brilliantly colored hummers, like the Violet-headed and Green violet-ear perform high in the canopy. The White-eared alternate between high and low perches. Leks are active during the nesting season for each species. Some species nest in the dry season. Others don’t start mating until the rains come.
The time of day for singing also varies. Rufous-tailed hummers start to sing at dawn and stop soon after sunrise. Blue-chested hummers perform in the morning and then again in the late afternoon. Hermits and Green violet-ears can sing all day long. Some of those that sing incessantly stop only long enough to wet their mouths with nectars and to chase away intruders. These males spend as much time singing in a day as the females do incubating eggs!
Alexander Skutch made an interesting observation while watching White-eared hummingbirds in Guatemala. The songs of the birds in any one lek were all very similar. But the songs of the same species in a different lek were so dissimilar from the first that until he examined the species carefully with binoculars, he thought they were different species. This has also been noted with hermit hummers. Since the leks are not geographically isolated from each other, it is unlikely that the different songs can be attributed to genetics. It seems more logical that when a young bird joins a lek, he learns and copies the prevailing song pattern. The intricacies of the hummingbird songs heard on leks might be the result of the relatively dark location where they are found. It is so dark that it is not suited to visual displays and this favors the development of distinct song dialects from lek to lek.
Within each lek, the most dominant males usually occupy the most central territories. Subordinate males are relegated to the edges of the lek. Males tend to return to the same territory in subsequent years unless they move into more central vacant territory. Most vacancies are due to the death of a male, but among the returning males there was little change in status. The turnover rate on a lek of Long-tailed hermits was about 50% a year. Contrasted with this, the turnover rate of the Green hermit in Trinidad indicated that almost all resident males survived at least two years.
Hummingbirds in South America are not the only birds to form leks. In this country, some male members of the grouse family, such as prairie chickens, Sharp-tailed grouse and Sage grouse, gather every year on leks where the males inflate brightly colored air sacs on their necks while “booming” and dancing. A female arrives, chooses a mate, and after copulation, leaves the lek to lay her eggs and rear her young as a single parent. In the case of Eurasian ruffs (members of the sandpiper family), a typical encounter would go something like this. A female arrives and makes her choice among the males competing for her attention. After an elaborate nuptial courtship, the mating is consummated then and there. With hummingbirds, this is not the case. Very few reliable observations of hummingbird copulation exist. Many naturalists have spent untold numbers of hours watching interactions on hummingbird leks. But the hummers streak off together and are lost in the dense vegetation. The complete courtship ceremony usually occurs at some distance from the lek.
In dense forests, the acrobatic pendulum flight like our hummingbirds in Arizona perform is not seen. The little hermits are charming in any case. The male bends tail and head up until he resembles a tiny boat that floats on an invisible cloud in front of the low- perched female. On wings that buzz more loudly than normal, he spends ten minutes or more darting back and forth in the area of about a foot, pivoting in mid-air, and dipping toward the object of his affection. She turns her head as she follows his every move. Skutch notes, “Once, at a distance from an assembly, I saw the wooer try twice to mount the one above whom he had performed, but each time she eluded his advances. A related hummingbird, the rufous hermit of South America, sticks out his long, white tongue toward the female, who warbles sweetly while watching him display before her.”
On the high plateau of Mexico where the landscape is more open, Helmuth Wagner recorded detailed accounts of the courtship flight of hummingbirds. Often when a female entered a male’s territory, the two flew closely side by side. Like a pair of Olympic ice skaters, they traced intricate loops and zigzags together, sometimes pausing to hover and face each other. But they always flew out of sight before the consummation of their courtship!
The more visually exciting the display of the male, the more brilliant and different from the female he appears. Think of the Anna’s male who flashes his rosy red head and gorget in front of a perched subdued-in-dress female to punctuate a 100 foot five at dizzying speed. The male and female hermits, as most hummers that form leks, are much more subdued and similar in appearance.
The more we discover about hummingbirds the more unusual and interesting they become. Even though our local hummingbirds have no experience with choral singing, their relatives in South America carry on an unexpected vocal tradition.