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

WRENDERINGS
Reports from the Field
Fall 1998

Birds' Response to Changing Habitat on the Floor of the Borrego Valley
American Bitterns Nesting at Camp Pendleton
The Heron and Egret Rookeries of San Elijo


Birds' Response to Changing Habitat on the Floor of the Borrego Valley

Eared Grebe, Double-crested Cormorant, Cinnamon Teal, Redhead, Surf-Scoter, Whimbrel, Greater Yellowlegs, and Least Sandpiper—the Salton Sea? No, Borrego Springs South, square G24! In one year the desert north of Club Circle Resort has been developed into an 18-hole golf course with four ponds, sodded greens, and an irrigation system.

The date palm grove on Foresome Drive was one of the first "clean-up" projects. These trees were neglected for decades. The dead palm fronts and sterile dates provided habitat for Barn Owls and Harris' Hawks and food for Scott's orioles an Coyotes. The trees have been replanted around the golf course, dividing the sanctuary of the grove as a whole. Horned Larks and Loggerhead shrikes have scattered to other parts of the valley with the loss of habitat.

The new ponds, however, provide a resting place for waterfowl we rarely see in Borrego. Green-winged Teal, American Wigeons, Canvasbacks, and Ring-necked Ducks appeared in G24 this year. For the first time in Borrego, a Forster's Tern was recorded on 29 and 30 March.

The development continues with the construction of 24 homes. In the future the nine-hole golf course that surrounds Club Circle will be redesigned and another nine holes will be added.

--Paulette Ache


American Bitterns Nesting at Camp Pendleton

Square E3 on Camp Pendleton contains a variety of habitats including coastal sage scrub, abused agricultural land, riparian woodlands, beaches, and coastal marshes. The area near the Las Pulgas exit off I-5 often has produced unexpected species of birds. After adopting the square in the winter, we found a Lark Bunting on 16 February 1998. On subsequent trips, as winter turned to spring, we found a pair of Northern Harriers in the marsh, Least Terns and Franklin's Gulls on the beach, and Yellow-breasted Chats and Bell's Vireos in the riparian areas along Las Flores Creek.

On several occasions this spring, we flushed from the marsh an American Bittern, a species whose successful nesting in San Diego County has never been proven. We were uncertain if we were repeatedly flushing the same bittern or if there were several. Donning "Aqua Socks," we entered the "swamp" water with vegetation higher than our heads to search for a bird emitting a strange call. An adult American Bittern flushed, but the call persisted. Rich swears he was within 6 feet of the sound, which seemed to travel around him while the grasses did not move.

On the following weekend, 6 June, Susan followed the bittern's "pumping" sound and watched one fly out while the call persisted. Moments later two bitterns of different sizes flew into the air. As they landed, an adult bittern flew up to join them--a total of three birds in the air at once. Needless to say, she was stoked!

On 24 May we noticed disturbances to the marsh where we had earlier seen the American Bitterns and a pair of Northern Harriers. Within the next several weeks, a road crossed the marsh and drainage pipes were added. On 3 July a well-driller told us he was drilling a 600-foot-deep well. Eventually treated sewage will be pumped into the well and raise the water table.

--Richard and Susan Breisch


The Heron and Egret Rookeries of San Elijo

Getting San Elijo Lagoon as one of my assigned squares for the Atlas project was quite a plum, but I guess you know the assignment also came with a bit of pressure. Every birder in San Diego visits San Elijo once in a while, and I figured a lot of people would be looking over my shoulder. I decided I would just plug away and do my best. So when Mary Beth Stowe spotted a Broad-billed Hummingbird last winter, Mona Baumgartel had that Sandhill Crane in April, Ginger Rebstock reported a Virginia Rail with chicks, Freeman Hall called in with a juvenile Frigatebird, and Barbara Moore's entire birdwatching class got a Clapper Rail with chicks, I just shrugged my shoulders philosophically. Ah well, I told myself, it's just a question of being in the right place at the right time.

But while I could be philosophical about a few toughies, I knew there were some target birds I'd have to get if I ever hoped to show my face at a future WingDing. Being dedicated birders, we've all been guilty of stealing a couple of quick looks down at the San Elijo Lagoon while speeding past on Interstate 5. And more often than not we've been rewarded with a glimpse of a Great Blue Heron or a Great Egret stalking the wetlands below the freeway. As I started working my first Atlas breeding season last year, I assumed the Blue Herons and Great Egrets were nesting nearby. How tough could it be to find a colony of 30 or more nests, some approaching the size of a kid's treehouse, populated by birds with maybe a four-foot wingspan? Tougher than you'd think.

Freeman Hall told me early on about the Snowy Egret and Black-crowned Night Heron nesting colony located about a mile south of the lagoon near the corner of Lomas Santa Fe and Sierra in Solana Beach (square M7). The colony consists of about 30 nests in the canopy of a large fig tree. The egrets and herons fly back and forth between the lagoon and the nesting colony and are easy to spot. Another small colony of night herons is located in a couple of scrawny eucalyptus trees several blocks farther south, across the street from the Solana Beach post office. Walking under either of the nesting sites during the season reveals a lot of whitewash, some broken eggshells, and an unfortunate chick or two fallen from their nest.

But these were the small egrets and herons. Where were the big guys? I read about a Great Blue Heron colony in some towering pine trees about two blocks southeast from the Carlsbad Library (I6). When I checked it out it was great to see, but the adult herons seemed to be flying north to Buena Vista Lagoon for their foraging. This wasn't the colony servicing the San Elijo flock.

As the 1997 breeding season came and went, so did the Great Blue Herons and Great Egrets of San Elijo. I watched them fly off toward the east each day and disappear, and I never could figure out where they were going. Toward the middle of the summer, a number of juvenile herons and egrets joined the adults in the main lagoon. The juveniles were marked at first by their spotty plumage and inexperienced foraging techniques, and I watched them mature and gain their skills as the year went by.

Then one day in early February I was driving east on Encinitas Blvd., where the road crosses over Escondido Creek, changes its name to La Bajada, and slips into Rancho Santa Fe (L8). I noticed a Great Blue Heron flying overhead. I casually kept glancing up at the bird as I continued to negotiate the road, and then I thought I saw it glide down toward the top of a stand of tall trees. The only place I could quickly pull off the road turned out to be a private driveway, so there I was, stopped in front of the fancy electronic gates of one of those Rancho estates. I grabbed my binoculars, jumped out of the car, and began scanning the trees way off beyond the gates.

I didn't hear the pickup truck pull up beside me, but a male voice asking me what I was up to caught my attention. I apologized, and explained my mission. He turned out to be a friendly Aussie, described himself as the caretaker of the property, confessed to a hobby of building rustic birdhouses, and asked if I'd like to come inside the gates for a closer look. Sometimes it's just dumb luck.

I followed my new best friend down the long winding driveway, and we pulled up and parked next to some horse stables. The riparian habitat of Escondido Creek ran along the entire western edge of the estate. A grove of eucalyptus trees had become established on a berm of high ground in the middle of the willows and mulefat along the creek. A nice-sized pond of fresh water and cattails sat between the trees and the white wooden fence of the horse corral. And there up in the lofty reaches of those trees, in numbers I still haven't been able to count accurately, were a whole bunch of large bulky stick nests just brimming with Great Egrets and Blue Herons.

That first day I counted about 30 nests, maybe fifteen with Great Blue Herons sitting in them, ten populated with Great Egrets, and five empty at the time. The nests consisted of large platforms of sticks, twigs, and tule stems. Some were only about two feet wide and fairly insubstantial, while others were over three feet wide and just as deep. Nest building was going on in earnest, and every few minutes another bird circled the trees and arrived with fresh nesting material. The male herons and egrets reportedly bring sticks to the tree while the females build the basic nest over the course of about two weeks. The nest gets repaired and added to throughout the season and is often reused in subsequent years. The caretaker told me this colony had been here for a long time, five or more years. He also said it used to consist primarily of Blue Herons but this year it seemed a lot more Great Egrets had joined the colony. A number of birds were sitting in their nests, presumably on eggs.

I came back a week later to have another look. I noticed that the Blue Herons had all the highest nests, without exception, the Great Egrets being relegated to the less desirable lower reaches. I climbed the fence and made my way into the boggy area under the rookery and discovered several broken eggs, confirmation of egg-laying during February. I also discovered the colony extended into another large eucalyptus tree that had been shielded from my view during my first visit. I now estimated the number of nests to be between 50 and 60, split roughly evenly between the egrets and the herons. I observed a pair of Great Egrets copulating in their nest, another entry on my life list of fascinating sights! I couldn't see any Snowy Egrets or Black-crowned Night Herons. Perhaps they found the competition with their bigger cousins too discouraging and preferred to set up their own colonies in their own neighborhoods.

During March, the colony survived relatively unscathed the heavy winds and driving rain and hail brought by several storms whipping through Encinitas. By the first week of April heron and egret nestlings could be seen poking their heads over the edges of their nests. Allowing 4-5 weeks for incubation confirmed a February egg-laying date.

By May I observed almost fully fledged nestlings of both species standing up on the edges of their nests, engaged in experimental wing flapping. Adults flew in to the colony every few minutes, touching off the raucous din of begging chicks. Nestlings in the colony seemed to represent every stage of development, from the fluffy-scruffy to the well-feathered. The larger chicks, often three to a nest, were so aggressively competitive about their feeding that adults were forced to make offerings from a perch on adjacent branches. Active young ventured out on the limbs, seeking a feeding advantage over their nestmates. On every trip I observed the ongoing process of nest building and repair.

As I write this, it is now late July, and the colony is still quite active. My caretaker friend told me the birds were usually gone by mid-June in years past. At last count there were perhaps 20 nests still with unfledged chicks, and some appeared to be only a few weeks old. Mostly it's the egrets who are still at it, although there are a couple of late-breeding herons as well. The extra rainfall this year seems to have had a positive effect on the success rate of this rookery. Could individual Great Blue Herons and Great Egrets be having second clutches in this particularly productive year, or are late-breeding, second-tier adults taking over some of the nests used by earlier-breeding adults?

I'll find out more about the Great Blue Herons, Great Egrets, Snowy Egrets, and Black-crowned Night Herons of San Elijo as I continue to observe their colonies over the next several years. As for other species, I'm sure one of you will happen upon a Green Heron nest one of these days at San Elijo. And if a pair of Little Blue Herons should stray up to San Elijo one of these days, I trust one of you will discover it first. But that's OK. After all, I've got breeding confirmation on my main heron and egret species. And I'd be able to hold my head up high if it weren't for this painful crick in my neck I seem to have developed over the last four months.

--Andy Mauro

birdatlas@sdnhm.org

Fall 1998 Wrenderings | Wrenderings Archive | Bird Atlas Introduction