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

WRENDERINGS
Reports from the Field
Summer 1999

Confirmation Cues
Vaux's Swift Attacks
Wildlife of Los Coronados Islands
Floodgates Open: Migrants Attack San Diego County


Confirmation Cues

In the Fall 1998 issue of Wrenderings I suggested some techniques helpful in confirming birds' breeding. Several participants' experience suggests a few more.

Stand back. As birders, all of us enjoy seeing birds as close up as possible. But such a distance is sometimes too close for birds to feel comfortable going about their business, especially when they are nesting. So if you suspect a bird may be nesting, stand back as far as you can see what it's doing through binoculars. If you're back even farther and use a spotting scope, so much the better. At this distance almost no birds will consider you a threat and resume their normal activities.

Watch the female. In sexually dimorphic species, the colorful males often attract and hold our attention first. But in many of these the cryptically colored females are the ones responsible for most of the interesting breeding behavior. In some species, such as the hummingbirds, any behavior that confirms breeding must be by the females. So after you've located a pair, stand back and focus on the female for signs of nesting. Of course, knowledge of the roles of the sexes in each species is the most useful. For example, in many songbirds the female is largely or entirely responsible for nest building, but we now know that in the California Gnatcatcher the male takes the leading role in that task.

Develop a "search image." Once you've found a nest or two of a species in a square, use your experience to look for nests of the same species in similar situations in other squares you may visit. And ask other observers for their tips. For example, Paul Jorgensen has found Scott's Oriole nests consistently by looking under the leaves of the tallest Spanish Dagger or Mojave Yucca (Yucca schidigera) growing in the oriole's territory. In a recent visit to square H23, Camel Rock, I profited from Paul's experience by finding an old Scott's Oriole nest on the ground underneath a yucca—the shape and texture of a Scott's nest is like a Hooded's. Certain other species I can now confirm easily by taking advantage of their characteristic behavior—Bushtit nests hung among the slender vertically drooping twigs at the edge of a live oak, shrike nests in isolated thorny shrubs, female Black-chinned Hummingbirds building nests by plucking the fuzz from sycamore leaves. If you have discovered a trick for confirming a particular species, please let the rest of us know!

--Philip Unitt

Vaux's Swift Attacks

A nightmare from an Alfred Hitchcock movie: birds pouring down a chimney and into the living room to trash the house, if not attack the people inside. It happened again several times this spring, in La Jolla and Carlsbad. Vaux's Swifts pass through southern California twice a year in migration between a winter range in the tropics and a breeding range in the Pacific Northwest. Originally, they used hollow trees for their communal roosts. Now they are attracted to man-made structures, especially chimneys, recalling their close relative the Chimney Swift. A cold, windy April seems to have concentrated them near the coast this year and led to fateful encounters with chimneys, much like the one atlas participant Mary Mosher suffered back on 26 April 1960.

Alfred Gross reported on Mary's experience in the Massachusetts Audubon Society Bulletin, reprinted in the July 1993 San Diego Field Ornithologists' Skimmer: "150 individuals poured into the living room, causing pandemonium as they dashed from one side of the room to the other and entered every room or closet wherever a door or passageway chanced to be open.... One became entangled in Mrs. Mosher's hair.... The most revolting damage was done by the viscid excrement the birds deposited on the carpets, furniture, art works, bed spreads, pillows, books, etc. Matters became so serious by 8:00 PM that the police were called, and four of the neighbors responded in the battle with the swifts. The birds, stunned by the impact of striking the walls, were scooped up with dust pans and shovels and carried outside in baskets covered with bath towels. Mrs. Mosher observed from the terrace, however, that a number of revived individuals flew back into the chimney, while others dashed against the windows in an apparent effort to get back inside the house.

In desperation a fire was lit in the fireplace to prevent further invasion. A number of birds were burned and their bodies dropped to the bottom of the fire pit. One bird, its plumage ablaze, dashed from the pit and nearly started a fire before it was swept down with a broom from an inflammable drapery....

Moral of the story: If your house has a chimney, have it examined from time to time to be sure that it is protected by grillwork and that the grill has not deteriorated as was the case with Mary's house. Don't wait for the next invasion of Vaux's Swifts. You might be too late." And Mary's insurance didn't cover the damage.

Mass mortality when migrants are highly concentrated could be a serious threat to Vaux's Swift, already of concern as a species nesting primarily in old-growth forest. Mary Platter-Rieger discovered such an event a few years ago when a flock was cooked in a boiler at the navy submarine base on Point Loma. If your chimney has a damper, close it before the first of April and you may allow the swifts a peaceful, safe night's sleep on their long migration. Failing this, ensure that the top of the chimney is screened. And tell your neighbors to safeguard themselves and the swifts, too, helping make San Diego County as swift-safe as possible.

--Philip Unitt


Wildlife of Los Coronados Islands

For the past two springs the Chula Vista Nature Interpretive Center has offered nature-based trips aboard the Mustang out to Los Coronados Islands. Last year (1998) was a wet El Nio year. This year has been a dry La Nia. We could really see the difference. In 1998 in the bottom-trawl sample from San Diego Bay we saw pretty much ordinary things, several kinds of flatfish, lobsters, and various invertebrates. The 1999 trawls and plankton grab found more exciting creatures. Have you ever seen a Ragfish? I hadn't. We found plankters (that's oceanographers' lingo for zoo- and phytoplankton) that were not on our "common plankton of San Diego" chart. On our island trip we found small bottom-feeding jellyfish, just like the ones we have been finding in the bay, called polyorchis.

White-sided Dolphins spotted our boat, thrilling everyone at bow riding. The seas were full of bright red Tuna Crabs being fed on heavily by hundreds of Western Gulls. Basking on the surface of the water were a Common Mola or Sunfish and a Slender Mola, both fish from more tropical waters. On the beaches of the islands were hundreds of Elephant Seals, California Sea Lions, and Harbor Seals, each species guarding its own territory. Curious young animals came out to inspect us. The cliffs rang with the echoes of their barking.

But best were the birds. In 1998 there were some birds on the islands, but not like 1999. There were just a few species but for some like the Western Gull and Brown Pelican there were hundreds of birds on nests. Downy white pelican chicks glowed like angels as they exercised their wings in the sunlight. Brandt's Cormorants sat regally on their nests, showing off their turquoise blue gular pouches, while Double-crested Cormorants sported their two white crests. Nearby sat the biggest surprise: six Brown Boobies. Could they be checking out nest sites, for an enormous northward leap in their breeding range? Last year we saw two pairs of Black Oystercatchers; this year there were about 30, clumsily moving over the mussel beds with their distinctive cry. One bird wore the black and white plumage of the American Oystercatcher. We even saw a Great Egret among the gulls. Everywhere you looked there were birds.

The trip was the same weekend as the Anza-Borrego Desert blockbuster. When I described the abundance of birds we had seen to Phil Unitt he bemoaned the lack of birds in the desert, blaming La Nia. Every year is different and always brings surprises. We will probably make the same trip next year. Contact me at the Chula Vista Nature Center (619-422-2481) for more information!

--Barbara Moore


Floodgates Open: Migrants Attack San Diego County

Pete Famolaro, atlas participant and biologist for the Sweetwater Authority, called me on Monday 9 April complaining that very few of his Least Bell's Vireos had arrived on schedule at Sweetwater Reservoir. This year, reports of the late arrival of this well-studied endangered species were rampant. To investigate further, I compared arrival dates with weather patterns over the past five years. I found a strong correlation between weather pattern and the arrival of not only Bell's Vireo but several other migratory species including the Nashville Warbler and Warbling Vireo. When Pete called, the southernmost projection of the jet stream had settled just south of us over northern Baja California. The forecast predicted the low pressure to move to the east within a day or two. I told Pete to expect his birds by Thursday. Both forecasts came true, and the vireos are now back at full strength.

A parallel event occurred during the week of 18-24 April. The weekend of 23-24 April a large volunteer work group gathered to help dig pitfall traps in San Felipe Valley (I21). In cooperation with the Museum and the California Department of Fish and Game, we are surveying the land recently acquired by the Fish and Game Department in the valley for reptiles and mammals. So we weren't even birdwatching—I used field glasses only to identify a Prairie Falcon, the Gray Flycatchers, Cliff Swallows, and Vaux's Swifts—but we couldn't help noticing the wave of migratory activity that was flowing up the valley. We found numerous expected migratory species including Wilson's, Yellow, and Nashville Warblers along with Warbling Vireos, Western Tanagers, and a remarkable eight Gray Flycatchers. Of particular note were 320+ Western Bluebirds, on an extremely late date for large numbers of this species away from its breeding habitat, and the largest number of Black-headed Grosbeaks I have ever seen in a day: at least 620! The birds passed by in flocks of 30 to 40 and were perched even on the road. Numerous birds went uncounted. Surely San Felipe Valley, leading northwest to a low pass to the coastal slope, is a key route for spring migrants, used more heavily perhaps than any other in San Diego County.

--William E. Haas

birdatlas@sdnhm.org

Redhead chick sketch by Nicole Perretta

Summer 1999 Wrenderings | Wrenderings Archive | Bird Atlas Introduction