Surprise in the Skies

By Bruce Haak, Nongame Biologist Southwest Region Spring was looking a bit bleak for downtown Boise's peregrine falcons. After three consecutive years of producing young in the nest box on One Capital Center, located at 10th and Main Streets, the pair seemed to be settling into their urban surroundings. Then last fall, the female peregrine vanished. As word spread of her obvious demise, the cadre of downtown falcon-watching faithful braced themselves for a dull summer in 2006. But as Yogi Berra is fond of saying, "It ain't over Ôtil it's over." In late April of this year, a juvenile female peregrine suddenly made an appearance at One Capital Center. Her presence there was unusual for two reasons: first, one would expect an un-attached adult female peregrine to be attracted to a vacant territory. In healthy peregrine populations, as in many wildlife populations, there are surplus adults, called floaters, milling about, anxious to fill the void left by a deceased breeding adult. Second, peregrines are generally not sexually mature until they reach three years of age. It takes time to develop the hunting skills necessary to feed a growing family, as well as to learn the skills of parenting (raising peregrine kids isn't much easier than raising human ones). As such, most one-year-old peregrines simply do not breed. Even when they do so successfully, they typically raise small broods. So it was with much surprise that, on July 1, Fish and Game biologists documented the presence of three baby peregrines in the nest box high atop the One Capital Center building. The chicks were 21 days old and just the right size for leg banding. And the three kids in the nestbox blows away the national average of 1.5 young peregrines per nesting pair. For most of the year, peregrine falcons are solitary predators that migrate back and forth annually from northern latitudes to Central and South America. Normally, adult peregrines seek mates during March, lay and incubate eggs in April, and raise young during May and June. Young falcons hang around the nest or eyrie for about a month before dispersing to parts unknown. The peregrine falcon courtship ritual is, in a word, elaborate. Because male peregrines are approximately 30 percent smaller than females, they first want to ensure that a prospective female views them as a mate, and not simply as their next meal. In preparation for mating, male peregrines perform high-altitude aerobatics. If his showing-off is well received by a female, the male begins feeding her. Finally, the pair strikes out in search of a suitable place on which to lay their eggs. Typically, this is a ledge, pothole or cave located high on a cliff. Unlike most birds, falcons do not build their own nests out of sticks and twigs. They simply scoop out a shallow depression in the sand or gravel and deposit their eggs. As long as the eggs can't roll off the cliff and the ledge is large enough to accommodate future growing young, the site is acceptable. From a peregrine's standpoint, the plywood nestbox atop the One Capital Center building, with its protection from weather and six inches of pea gravel lining the floor is a penthouse apartment. When the male shows the female that he is a good provider, she begins the process of producing eggs. Normally, a female lays three to four eggs per clutch, incubating the eggs for about 32 days. For peregrine chicks, their's is what you might call an accelerated childhood; they reach full size in just 45 days, and take their first flight soon after. Most young falcons frequent the nest area for about a month, learning how to fly and hunt, before dispersing. This year, the chance to see these young aerialists zooming about downtown Boise will come during the heat of summer. But if you are like me, a pleasant surprise in the sky, even a late one, is a welcome sight.