San Diego Natural History Museum--Your Nature Connection[San Diego County Bird Atlas Project]

WRENDERINGS
The quarterly newsletter for Bird Atlas volunteers
Fall 2000

Successful Nesting of Harris' Hawks at Boulevard
Housing Shortage Affects Local Birds


Successful Nesting of Harris' Hawks at Boulevard

[Harris' Hawk.  Photo by Tony Mercieca.]
Harris' Hawk

In 1994 southern California welcomed a remarkable incursion of immigrants from south of the border: Harris' Hawks. Nearly 50 individuals were seen during the mid 1990s, many of these in San Diego County. Up to nine were in McCain Valley north of Boulevard, up to eight around Borrego Springs, and six scattered elsewhere. In December 1994, when I visited Boulevard and saw one of the birds on the property of Leslie Mauris, Leslie showed me a photo she had taken of six huddled together on a phone line. Gregariousness and sociality are a key aspect of the biology of this remarkable raptor.

Leslie also showed me a nest high in a coast live oak she said the hawks had used, and over the next three years I heard a few other stories of Harris' Hawks nesting in the Boulevard region lall too late to be checked out. Then atlas participant Frank Unmack renewed our contact with a key person in Boulevard, Randy West. Randy filled us in on many missing details of the story: there had been a maximum of nine individuals, but four had been killed in various mishaps; the Boulevard birds arrived even before the wider-scale incursion of 1994; they had nested every year but never, to Randy's knowledge, fledged any young. In only one year did he see even a chick in the nest. This year the nest was only a quarter mile from his home, and he and Frank monitored it through late May. The nest is on a private ranch, requiring permission from the landowner to be viewed. Fortunately, Randy, as a neighbor, was able to make the arrangements.

On 1 June Randy called to inform me that at least one chick had hatched. Then on 1 July he called with the news that two chicks had fledged the first successful fledging of wild Harris' Hawks in California in about 40 years! Such an event calls for good documentation, so on 12 July we arranged to take photographer Tony Mercieca out to record the fledglings on film. Soon after we arrived at the grove of oak trees containing the nest Randy spotted one of the young, sitting quietly under the canopy. Then another came flying toward us, landing on a phone pole. This was the most active fledgling, and Tony got many stunning photos of it. The other fledgling spent most of its time sitting passively just 2 feet from the nest. At one point both fledglings tried to hop back into the nest. A scuffle ensued, and three young Harris' Hawks flew out! Evidently a third fledgling had been sitting inside the nest unseen. All the young were still awkward on their wings and feet and not yet feeding themselves, just waiting for the return of the adults. As of 9 August, Randy reports that the family is doing well, the three young accompanying their parents as they hunt.

Michael Patten and Richard Erickson have a paper in press in the Journal of Raptor Research chronicling the history of Harris' Hawk in California; thanks to Michael for sending me a copy of the manuscript. Throughout recorded history, California has been marginal to the species' range, and numbers here have fluctuated widely. In the 1920s hundreds occurred in the Imperial and lower Colorado River valleys. The numbers dwindled in the 1950s, and by 1964 the species was extirpated from California. The nearly total loss of native riparian woodland from southeastern California has been commonly assumed as the main factor responsible. From 1979 to 1989 attempts to reintroduce the species along the lower Colorado were made, and some of the released birds nested and fledged young. The reintroduction failed to take root, however, and few if any Harris' Hawks remain there. Likewise, the birds around Borrego Springs were seen carrying sticks in 1994 and copulating in 1995 but are not known to have got even as far as laying eggs. The most recent sighting in this area is of a single bird on 22 March 2000.

Randy West is a licensed falconer and keeps two Harris' Hawks, of Texas origin, himself. The wild Harris' Hawks regularly visit his captive birds. I propose that Randy's birds may be responsible for the persistence and nesting of the wild individuals a raptorial version of the "Wild Animal Park effect." That is, just as the wading birds kept in captivity at the Wild Animal Park and Sea World have served as nuclei for colonies of wild colonial wading birds, Randy's Harris' Hawks are the nucleus for the "colony" at Boulevard. Besides the nesting pair, three other birds persisted in the area through the winter of 1999-2000, and one of these resurfaced as a "helper" when this summer's chicks hatched. The Harris' Hawk's highly social habits, entailing cooperative breeding, mark it as a candidate for the "Wild Animal Park effect."

--Philip Unitt


Housing Shortage Affects Local Birds

[Nutall's Woodpecker.  Sketch by Nicole Perretta.]
Nutall's Woodpecker

Charlie and I live in a semi-rural area of Poway in an old avocado orchard. Since we moved in a few years ago, we have placed several birdhouses in the yard with the hope of attracting cavity-nesting species. Prior to this year, we've had House Wrens and Western Bluebirds successfully nest in the houses.

This year, one of the birdhouses became the site of several anxious disputes over ownership. The birds had clearly heard the real-estate mantra "location, location, location," and several species vied for a house near the fountain (view!) and with convenient nearby branches for perching (ample parking). The first tenants were a pair of bluebirds who seemed quite satisfied with their selection. They defended their choice against occasional forays by a House Wren and a pair of Ash-throated Flycatchers. The bluebirds built a nest and seemed prepared to breed successfully--but, perhaps because of all of the competition, they never laid any eggs and eventually abandoned the box.

The Ash-throated Flycatchers then took possession and made improvements by lining the nest with a thick layer of fur. At least one egg had been laid when they began to have a visitor who had not read the "do not disturb occupants" sign. A male Nuttall's Woodpecker entered the birdhouse every morning and spent about an hour ducking in and out of the box. The flycatchers frantically attacked him each time his head appeared at the entry hole but to little avail. This went on for several days. Finally the woodpecker left the flycatchers alone, and they fledged two young in early July.

Lately, the Nuttall's Woodpecker has been back in the birdhouse, and he too is making improvements. It seems the entry hole needs some widening and reshaping. He's also been known to drum on the house, eliciting a pleasingly resonant sound. After all of the excitement surrounding the birdhouse this year, we can hardly wait to see who will move in next spring!

--Charles Van Tassel and Kirsten Winter

Harris' Hawk photograph by Tony Mercieca
Nuttall's Woodpecker sketch by Nicole Perretta

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Fall 2000 Wrenderings | Wrenderings Archive | Bird Atlas Introduction