In search of black oystercatcher nests in Southeast Alaska
Over 65 percent of the population of this rare bird lives in Alaska

By KRISTEN ROMANOFF

 

Courtesy of U.S. Fish and Wildlife Service Two of a kind: A pair of black oystercatchers perch along an Alaska shore. These are two of an estimated 11,000 birds nationwide.Scanning the shoreline through binoculars while cruising the perimeter of a rocky island, we hear the familiar loud, piping alarm call before spotting a lone black oystercatcher perched conspicuously atop a rock.
The sentinel, having sounded the alarm, quickly leaves its perch to lure us away. Somewhere nearby we are sure to find its mate, most likely sitting atop a nest.
Phil Mooney, Sitka area biologist with the Alaska Department of Fish & Game, slows the outboard of our inflatable Zodiac. The boat approaches the shoreline, as swells crest and break against the steep rock walls.
Mooney times the boat's approach as the swell rises above horizontal bands of barnacles and mussels. I have just enough time to leap onto the rocks.
Once onshore, I take a moment to observe the sentinel's movements. Oftentimes, one only needs to go in the opposite direction of the sentinel to come upon its mate, concealed amongst the rocks.
Clambering over boulders, I see a second bird take flight, marking the likely location of a nest. I search the gravelly area where the pair may have scraped away a shallow bowl or simple hollow.
Finally, I spot it. Barely above the high tide line, exposed to all of the elements, are three speckled eggs laying in a scrape adorned with broken pieces of white shell. Though it is completely out in the open, the oystercatcher nest is nearly invisible.
The pair's commotion and my continued presence stir up scores of gulls and at least a dozen other oystercatchers. The aerial chaos makes it extremely difficult to determine where to begin looking for the remaining nests. After an hour of searching, I find only two more.
The tide is falling, the seas are picking up and we're losing daylight. We load the Zodiac back onboard the landing craft and head for a cove where we will spend the night, before heading out again the following day to look for more nests.
Black oystercatchers have been identified as a species of high concern by federal and state agencies and conservation organizations in both the United States and Canada. The total population is under 11,000 birds, making it one of the rarest shorebirds in North America, and the status of the population is unknown. They range along the Pacific coast from Baja to the Aleutian Islands, but over 65 percent of the global population resides in Alaska.
These large blackish birds with long red bills and bright yellow eyes live exclusively in the upper reaches of the inter-tidal zone. The breeding habitat of black oystercatchers is associated with the high tide margin of the inter-tidal zone, usually near mussel beds. Using their flattened long bill, oystercatchers pry open mussels, limpets and other invertebrates. They nest on gravel and shell beaches or on rocky islets that are not heavily forested.
Their year-round dependence on this narrow band of habitat makes these birds particularly vulnerable to both natural and human disturbance. Predation by mammals, such as mink, river otters, and bears - as well as gulls, ravens and eagles - takes a toll on oystercatchers. Eggs and newly hatched chicks are particularly hard-hit.
Because their nests typically crowd the high-tide margin, they are extremely susceptible to flooding by extreme high tides, storm surges and large boat wakes. Because recreating humans tend to prefer the same gravel beaches vital to breeding oystercatchers, campers and kayakers may inadvertently disturb nesting birds or even trample their highly camouflaged nests.
Coastal contamination can severely impact oystercatchers, as demonstrated by the 1989 Exxon Valdez oil spill, in which 20 percent of the oystercatchers in the spill area were killed immediately by oiling. Birds not directly oiled were faced with eating oil-contaminated prey or starvation.
"The oil spill had devastating short-term impacts and, as we are finding out now, long-term impacts as well," said David Tessler, a research biologist with the Alaska Department of Fish and Game. "Some current research shows that oystercatchers are still carrying physiological effects from feeding on prey in oil contaminated areas."
Tessler points out that in the aftermath of "the infamous oil spill, wildlife managers realized just how little we really knew about this highly conspicuous species. Virtually nothing was known about their population size, status, life history, productivity, threats, demographics or even migratory movements."
In Alaska in 2003, several agency scientists and conservation organizations founded a working group to exchange information on the current state of research on this species, define future research priorities and coordinate efforts across the state. A year later, the International Black Oystercatcher Working Group was formed, bringing scientists together to address research and management for oystercatchers across their entire range.
The Alaska Department of Fish and Game took the lead in coordinating new cooperative studies on productivity, survival, genetics and seasonal movements, all of which are currently underway. Tessler has ongoing research and monitoring programs in Prince William Sound, on Middleton Island, in Kenai Fjords and Glacier Bay National Parks, and with Canadian collaborators at locations in British Columbia.
"We are going to know so much more about this bird by the end of 2006 and 2007," said Tessler. "At that time, we will have a pretty good handle on this species."
The information from these studies will inform a new range-wide conservation plan for oystercatchers that Tessler and co-authors at the U.S. Fish and Wildlife Service plan to complete by October 2006.
There has never been a population census for black oystercatchers, and the only population estimate ever done used spotty data collected incidentally during seabird surveys. Given the limitations of that 15-year-old estimate, biologists would like to know what the actual population is.
"Even if the population is twice the original estimate, oystercatchers are one of the rarest birds in North America," Tessler said.
Over the last five years, the Forest Service conducted an oystercatcher survey for Prince William Sound. But surveying Southeast Alaska is quite another matter. Because there are over 15,000 miles of shoreline in Southeast Alaska, it would be virtually impossible to survey the entire coastline. But knowing something about oystercatcher "hot spots" would make it possible to survey and monitor only the most likely areas.
The survey trip that I participated in along the outer coast of Baranof Island was part of that larger effort to find important oystercatcher breeding sites. It was one of five preliminary surveys in Southeast Alaska conducted by the Alaska Department of Fish & Game this summer to locate oystercatchers and determine their breeding densities.
A handful of island groups on the outer coast were targeted for these surveys: remote rocky islets and gravel beaches, relatively free from human caused disturbances and free of most predators. Pairs of biologists conducted the southeast surveys in mid-May through June after eggs had been laid, but prior to chicks hatching.
While isolated islands with several nesting pairs on each were found, we have not found breeding densities comparable to those found in Prince William Sound, Middleton Island, Glacier Bay or Kenai Fjords.
Once anchored for the night, Phil and I talk about all of the possible factors influencing the relatively low number of breeding pairs that we've found. Phil reminds me that, while not finding a treasure trove of oystercatchers, we are still uncovering valuable information about the choices that oystercatchers are making in determining where to breed.