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

WRENDERINGS
Reports from the Field
Summer 1998

Rockwrenderings: It's a desert out there—Or is it?
El Niño in the Anza-Borrego Desert
Caught in the Storm—waterbirds down on Inland Lakes


Rockwrenderings: It's a desert out there—Or is it?

When we decided to adopt a square for the bird atlas, our only constraint was that it give us an excuse to use Karin's four-wheel drive truck to go play in the desert (on existing roads, of course!). So when we were assigned square G29, Five Palms Spring, we had no idea what to expect. We did, however, notice that our target list was considerably shorter than all the others -- a whopping 17 species for the breeding season. (Hmmm… wonder if we'll se anything at all….) But then again, a square with a few birds and little cover sounded like an easy one. And the prospect of exploring a new area and seeking out new birds was exciting, so we eagerly set out to five Palms Spring. Aside from the palm oases, which have some permanent water, the square turned out to have a rather bleak combination of mud-hill badlands, sandy washes with occasional thorny shrubs, and sparsely vegetated creosote scrub flats. Not much in the way of good nesting habitat. So the results so far have been surprising: 9 species confirmed, 4 probably, and 6 possibly breeding -- 112% of our target species. And the total breeding and nonbreeding species count has reached 48. Certainly more than we expected. And there were other lessons for us as well...

Lesson #1: Desert birds breed early. On our first trip in April 1997, we discovered that much of the breeding activity was already over. Our initial discoveries included several recently used but empty nests, and full-grown Costa's hummingbird fledglings being fed by mom. But we also found nest-building Loggerhead Shrikes and Black-throated Sparrows, indicating that some other species were just starting (or re-nesting). So in 1998 we planned weekend trips in March, April, and May to catch all phases of breeding activity, and we bet February wouldn't be too early.

Lesson #2: Warblers don't read the field guides. Our careful keying out of the LYB's (little yellow birds) hiding in isolated thorny shrubs yielded all sorts of species whose habitats include moist woodlands, forest edges, thickets, spruce bogs, and coniferous forest. Not quite how we would have described our square. But it turns out that there is a bounty of insects in the blooming mesquites, providing a feast for migrating birds. And the good part is that most of these warblers are a lot easier to see in sparse, low desert vegetation that in their "normal" lush habitat! Our first two trips yielded 7 warbler species: Wilson's, Townsend's, Orange-crowned, Black-throated Gray, Nashville, Yellow-rumped, and Hermit Warblers. Other unexpected (to us, at least) species have included the Warbling Vireo, Black-headed Grosbeak, Summer Tanager, Western Tanager, Hooded Oriole, Bullock's Oriole, Lark Bunting, Western Meadowlark, Empidonax flycatchers, and assorted swallows (Tree, Violet-green, Rough-winged, and Barn). And then there were the Lesser Goldfinches -- feeding fledglings! Even some of the expected species yielded surprises: LeConte's Thrashers didn't seem all that secretive -- we found several individuals, including a foraging pair and one bird taking food to a well-hidden (but ultimately found) nest! And the "expected" Greater Roadrunner, Cactus Wren, and Black-tailed Gnatcatcher were nowhere to be found.

Lesson #3: Raven has a hard life out there. Our nest finding in 1997 along the mud cliffs of Basin Wash included on recently used next (#1), one not-so-recently used nest (#2), and on failed nest (#3), which had been crushed by the collapse of rocks above the ledge it was on. In 1998, nest #1 had been washed out and was scattered along the cliffs and ground below. Nest #2 had apparently been re-used this season, but failed when the ledge it was sitting on gave way. It looked like the broken eggs or young chicks were still stuck to the cliffs below the sit. Nest #3 -- the previously failed site -- had a new nest built on top of the rocks on top of the old crushed nest, with Raven herself perched at the summit. Does persistence pay?

Lesson #4: Horned Larks don't read the field guides either, or How about those badlands? One of the biggest surprises has been how many species breed in the most desolate part of our overall desolate square. Much of our square consists of badlands, or eroded mud-hills with very little vegetation. The Raven nests in the mud cliffs were not unexpected since those cliffs are the only tall structures in our square and Ravens can forage widely. (We wonder if the Kestrel we keep seeing in that area is breeding there as well). But we also confirmed Rock Wrens, House Finches, and Horned Larks breeding in the badlands, with White-throated Swifts suspiciously flying in and out of cracks, and one failed hummingbird nest (with dead chick). This area also contains small caves that Say's Phoebes use to roost and/or to sit out the heat of the day. The mud cliffs at least provide some structure for Ravens, Rock Wrens, and Say's Phoebes to use. The Horned Lark nest was beside the road in an area with nothing but low rounded mud hills and a few clumps of grass. Certainly not the flat areas Horned larks are supposed to prefer. And it doesn't seem like the area would have enough food to support the adult birds, much less breeding.

Lesson #5: The isolated-thorny-shrub method. It works. If there is a suitable-sized isolated thorny shrub, it will have a nest. Just go look. (They can be very well hidden in those mistletoe clumps.) But they have to be isolated thorny shrubs. If there are too many shrubs, they won't all have nests, as we discovered in other, more lush squared on the blockbuster weekend. Corollary to the isolated-thorny-shrub theory: any cholla cactus higher than 2 feet has at least on House Finch nest.

Lesson #6: House Finches rule!

--Karin Forney and Ginger Rebstock


El Niño in the Anza-Borrego Desert

Anza-Borrego Desert State Park has been exceptionally wet this year with about 10 inches of well-distributed rainfall, 4 inches above average. No one here can remember such a steady winter crop of annual flowers on the desert floor. Carpets of flowers began in October 1997 and lasted until early April 1998, providing the best spring bloom in six years. Perennials are still going. The last two years of drought, averaging less than 3 inches, caused a conspicuous crash in population s of many local birds, such as the California and Gambel's Quail, Cactus wren, Black-tailed Gnatcatcher, and Least Bell's Vireo. Rabbits and hares were virtually absent—which I speculate as the cause for several pairs of Golden Eagles failing to nest last year. El Niño has reversed the drought and I hope the down trend for wildlife. This spring the most noticeable changes I've seen include large flocks of wintering and migrating Brewer's Sparrows, early nesting for several birds (such as the Black-throated Sparrow), and widespread nesting by Lesser and Lawrence's Goldfinches. In fact, until this year we didn't have confirmed nesting for Lawrence's. It may be another season before we see whether this year's plentiful seed and insect crops translate into increased populations of such wildlife as the Cactus Wren, quail, rabbits, and eagles.

--Paul Jorgensen


Caught in the Storm—waterbirds down on Inland Lakes

Several waterbirds, such as the Black Brant, Surf Scoter, Common Loon, and Bonaparte's Gull, cross over San Diego County on their spring migration out of the Gulf of California. Normally they pass unnoticed high overhead, but storms may force them down onto inland lakes. Remember the snowstorm on April Fool's Day? Bill Hass, Scott Tremor, and I were driving to San Felipe Valley for a meeting with Randy Botta of the California Department of Fish and Game. The bad weather suggested that it could be one of those days, and when Bill noticed four Brant flying over Santa Ysabel we knew it. Scanning Lake Henshaw revealed around 300 Surf Scoters, with a flock of 40 Black Brant circling overhead. Dozens of Bonaparte's Gulls were foraging on small ponds near the lake, and a flock of 25 Turkey Vultures had probably been stalled by the storm, too. We continued on down Highway S2. Past the summit, the wind was blowing downhill ferociously. And another flock of ten Brant was fighting it sway uphill against the wind. A single Bonaparte's Gull trailed a few minutes later.

Other observers have noted some fallout of waterbirds inland, too. Mike Fugagli found a Surf Scoter on a pond in McCain Valley (S26). Mike Evans saw a Bonaparte's Gull heading up San Felipe Valley, probably the main migration corridor, on 25 April. And the same day Rich and Susan Breisch had a flock of eight cruising down Hauser Canyon (T21). On stormy days, many birders head to La Jolla to look for ocean birds blown toward shore. But in spring migration another option is to head to inland lakes, especially Henshaw, Cuyamaca, and Morena, to see what migrating waterbirds must ride out the storm.

--Philip Unitt

birdatlas@sdnhm.org

Summer 1998 Wrenderings | Wrenderings Archive | Bird Atlas Introduction