My field study site is as urban as it gets: I drive here via three different freeways, Oakland streets, a tunnel beneath a large channel in San Francisco Bay, and an endless expanse of concrete built on landfill--a former naval base. I arrive at a gate where a sign in both English and Spanish reads, "No trespassing. California Least Tern nesting area. An endangered species protected by law." San Francisco, just across the bay, feels close enough to touch.
|Meredith Elliott reviews field data on the California Least Terns breeding on former runways at the Alameda Naval Air Station. Photo by Chris Rintoul.|
This unlikely setting--the runway complex of the former Naval Air Station--is home to the Alameda Point Least Tern colony. Along one of the taxiways next to the colony I hear the terns' chorus of "squeaky-toy" sounds. Finally, leaving my car and strapping on binoculars, I enter the busy world of colonial seabirds. Adult pairs are feeding each other and their chicks, just as Least Terns have done for millennia--on the once pristine beaches of California.
Beginning in 2002, PRBO has been studying the diet and foraging habits of this colony. Our research is part of a monitoring program required for dredging operations in the Oakland Harbor, just north of the tern colony, and the work is sponsored by the Port of Oakland and the U.S. Army Corps of Engineers.
Reproductive success of the Alameda colony has declined in recent years, which may be attributed to their food supply. Understanding the diet of terns breeding here may give us insight about their prey resources and whether prey is limiting the growth of this colony.
|California Least Tern chick. Photo by Meredith Elliott.|
My coworker, Jennifer Roth, and I have several assignments. From a makeshift observation blind on the back of a pickup truck, we record size and any other descriptors of the fish that adults feed their chicks (the prey are too small to identify to species). Flying birds occasionally drop fish on the ground, and these we collect to try and establish what species are most important to terns. We also collect and examine fecal samples to find out which fish the terns actually consume. Results will help us determine the caloric intake of Least Tern chicks.
We also take our research on to San Francisco Bay, a nursery for the small fish that Least Terns consume. Aboard our research vessel, an 18-foot Boston Whaler, we try to discover where Least Terns forage on the bay. Piloting our boat along a predetermined route within a few miles of the colony, we search the skies for Least Terns and record where we observe them. Our 2003 results show that terns concentrate their foraging efforts in the shallow, nearshore waters south of the colony.
|Juvenile California Least Tern. © Peter Latourrette (www.birdphotography.com)|
Cruising, we're close enough to the San Francisco-Oakland Bay Bridge to see thousands of commuters making their way into the busy metropolis. My attention soon comes back to the terns. After a number of years studying this colony, I am still in awe of these little seabirds and the oasis they have made in such an urban environment.