FRIENDS OF EDGEWOOD NATURAL PRESERVE

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Most people who visit Edgewood Park look down, because that’s where the wildflowers are. I’m more interested in birds, so I tend to look up. In March of 1999 I happened to see a red-shouldered hawk (Buteo lineatus) fly overhead with a stick in its mouth. I was lucky enough to see its destination: the crotch of the large eucalyptus tree just south of the Stage Road parking lot. With its mate, this hawk was building a nest. I’ve watched that nest for the past three years as the hawk pair raised families of nestlings. You can see many photos of my observations at my web site, www.digibird.com. I couldn’t help but be fascinated by what I saw.

Red-shouldered hawks are far more likely heard than seen at Edgewood. During nesting season their loud, repeated “key-er, key-er, key-er” cry is audible throughout the lower valley. Unlike their familiar red-tailed cousins, red-shouldered hawks prefer forested areas and hunt from low perches. They are slightly smaller than red-tails, and are far less likely to be seen soaring. In flight, the easiest way to distinguish them is by noting the bold black and white barring on the underside of the tail. They tend to keep to the valley, while red-tails dominate the upper grasslands. Very beautiful birds with vivid coloring, they blend right in with the oak and eucalyptus foliage of the valley floor and are easy to overlook. Nesting season provides an unusual opportunity to study their behavior.

Birds only nest during breeding season, and once a successful nest is established most hawk species tend to reuse it. Edgewood’s hawks have maintained the Stage Road nest for at least three years, refurbishing winter damage each spring. The nest is comprised of small sticks, foliage, and adult down. From the Edgewood Trail, the nest appears to be an almost happenstance accumulation of eucalyptus debris wedged in a fork of the tree; however, this nest has survived for three years without significant damage.

The nest is several feet in diameter and may weigh over one hundred pounds, and is large enough to hold an adult and three full-size nestlings. (Most birds, including hawks, are full size when they fledge.) When the female is ready to lay eggs the hawks will decorate the nest with fresh green leaves and moss, and line the inside with their own down. The usual number of eggs is three; one egg is laid per day, so one egg will hatch per day, 33 days later.

Hawk parents must be among the most attentive guardians in nature. From the time the first egg is laid (for the Edgewood hawks, around March 15) to first hatch (April 16) both parents share incubation duties. Once hatching starts, however, their roles diverge: the female tends the nest and the male hunts for food. Nest duties require the female's continuous attention during the first two weeks. Since the nestlings lack feathers, the mother is the sole source of protection from rain, sun, and chill. A jay or crow could easily steal a hatchling, so mom is also primary defender of the nest. She will attack other birds of prey that wander into the nesting area.

The male's role is equally important: he's feeding the entire nest, including the adult female, and the success of the nest depends completely on his luck and skill. The nestlings' weight must double, on average, every eight days to reach the adult weigh of approximately one pound at fledging, 35 days after hatch. (At that rate, an eight pound human baby would weigh 128 pounds in 36 days.)

That growth rate requires a steady stream of reptiles and small rodents. Approximately once per hour the male leaves prey at the nest. The female tears the prey apart and feeds it directly to the nestlings, which beg with a whistling cry. Mom seems to try to distribute food equally among the nestlings. However, if food were scarce, the strongest (i.e., oldest) nestling would be fed first.

By their third week the nestlings show new feathering and mobility. Their feathers allow them better thermal control, so mom can spend less time at the nest--and more time hunting. Most of the nestlings’ time is spent sleeping or grooming their rapidly growing feathers. They appear far more alert to sounds and motion and can follow movement outside the nest (for example, walkers on nearby trails). This is a time of dramatic transformation. At such rapid growth rates, small differences in age—here, just two days—show acutely.

By week four, most feathers are in and the nestlings are strong enough for some exercise. They can walk purposefully around the nest and feed themselves from delivered prey. They also practice for fledging by grasping the nest with their feet and flapping their nest-spanning wings. They’ve got most of their flight feathers now and aside from some bits of down they finally look like true birds of prey. This is the plumage they will retain until they achieve sexual maturity next year. Even as adults, males and females look identical.

The Edgewood nestlings begin fledging on May 21, about 35 days after hatch. The first “flight” is mostly a hop to one of the branches supporting the nest. After a few minutes the fledgling hawk hops back to the nest. The younger nestlings appear fascinated by this.

Subsequent hops are more ambitious, and by the following day the fledgling really does fly to an overhead branch. The first few times the fledgling appears to nearly fall out of the tree. Its grasping skills are strong enough to compensate for poor landing technique; as it gets stronger and more efficient, its ability to stick landings improves greatly. Each nestling follows this pattern in hatch order, and after a week of practice the fledglings can fly the 30-50 yards to nearby trees. For me, this is a bittersweet time: I’m thrilled to see “my” babies take their first substantial flights, but I know that my ability to monitor their progress will greatly decline. As much as I try to stay detached, after six weeks of intensive observation I can’t help but feel like a surrogate parent to the nest.

For another week or two the fledglings will continue to sleep and feed at the nest. This is the last period during which they’ll be easy to see; once they learn to freeze on their perches, they become nearly invisible in the foliage. They’re not capable of hunting yet and will depend on their parents for food for many more weeks. The nest will be the center of a constantly expanding circle of exploration and experience as the fledglings learn necessary life skills. They’ll tend to stick together and will call to each other, and their parents, as they move around the valley’s trees. But by fall the family will disperse to unknown destinations. If all goes well the fledglings may live 15 years, and the adults will return to Edgewood next spring.

Send mail to wm at this domain with questions or comments about this web site. Copyright © 1999 - 2008 Friends of Edgewood Natural Preserve. Last modified: January 20, 2008.