On April 30th of this year, Nils Warnock and I set out from PRBO on the 14-hour drive to Boardman, Oregon, there to capture eight Long-billed Curlews for our study of these birds' year-round movements and habitat uses. The curlew, because of its small population and dependence on agricultural habitats, is a species of conservation concern. Our goal was to fit satellite transmitters on some birds nesting in the northern Great Basin and then be able to track them in California's Central Valley. This would help define the agricultural landscape that curlews need for overwinter survival (see Observer 152, Spring 2008).
|Preparing to release a Long-billed Curlew, in PRBO's study of the species' conservation needs. PRBO photo.|
By banding two curlews at Boardman in 2007, we knew that nesters from there would likely winter in the Central Valley. But tens of thousands of curlews use this critical area in winter--and the only reliable way for us to catch a few birds was on their nests. So Nils and I set out to travel more than 500 miles northeast within the species' world range.
Many curlews nest at Boardman on the rolling grasslands south of the Columbia River, at a naval bombing range and adjacent conservation area owned by The Nature Conservancy. Our first step upon arrival was to receive instruction from naval personnel on avoiding dangers from unexploded World War II ordinance scattered over the bombing range.
Afterwards, with our research partner Lee Tibbitts of the U.S. Geological Survey, we began our curlew searches. For eight hours we would walk through nesting habitat while scanning intently for well camouflaged incubating birds up to 20 feet ahead.
|In Oregon, Gary and Nils retrieve a curlew from the mist-net. PRBO photo.|
The first day we found three nests in the laying stage, including those of both males tagged the year before: they had returned to their exact territories. The next day we caught the males on all three nests and proudly discussed how we had uncovered curlews' nesting secrets. Subsequent long days of bone-weary walking, however, produced nothing--and proved that good luck was also needed to find curlew nests.
"Each day we eagerly await the signals that instruct us about how Long-billed Curlews move around. My days this fall and winter will also be brightened by memories of our springtime nest hunt."
When we did locate incubating curlews the birds would flatten themselves on the ground, relying on their mottled coloration for concealment. We usually approached to within 15 feet before spotting them, and frequently they did not flush even when we approached within six feet. They often chose nesting spots with the shortest vegetation, and I wondered if this enabled them to observe their surroundings while pressed close to the ground. Before a bird resumed upright incubating posture, for instance, it might need to be sure when a coyote (the curlew's main nest predator) had left the vicinity. Deciding whether to stay put or to flee when approached by a coyote must be difficult for a curlew: fleeing means destruction of the eggs, while staying put may prove fatal. These birds are courageous.
On May 5th we found three nests, again convincing us we had broken the species' nesting code. But on May 6th we failed to find more. Reviewing May 5th, we again realized the importance of luck: Nils found one of the nests when walking toward me to look at a meadowlark nest I had just discovered, and Lee found another by observing two curlews harassing a harrier. It turned out the harrier had been trying to eat the curlews' eggs, and after investigating, Lee reassembled the eggs in the nest. The following day, we were pleased to find a female incubating the nest and did not try to catch her.
|Can you spot the bird flattening itself over its nest in the grassland?
PRBO photo by Nils Warnock
We left on May 7th after tagging four males and four females to bring our total for two years to ten birds. Within hours our computers displayed their movements. Though one male stopped signalling--shed its transmitter or did not survive to make its fall flight southward--the remaining nine all migrated to the Central Valley. Pairs did not migrate or winter together, and the two males from 2007 returned to the same locations as they had the previous winter. Others spread out, from Visalia to Chico. Some are turning out to be travelers, especially one female that moved first to Visalia then north in two steps to Chico, in the process jumping over the Los Banos location of her mate.
A graduate student from Humboldt State University soon will commence field studies to expand our knowledge of the curlew's winter use of the Central Valley's agricultural landscape. Each day we eagerly await the signals that instruct us about how Long-billed Curlews move around. My days this fall and winter will also be brightened by memories of our springtime nest hunt.