Seabirds, shorebirds, and waterfowl -- the waterbirds -- possess amazing adaptations, enabling them to survive in rugged and exposed coastal and marine environments. The Common Murre, for example, lays an oblong egg designed to stay put on the narrowest rock ledge. The Black Oystercatcher, employing keen awareness of tidal cycles, nests within feet of the pounding Pacific l-- prime intertidal real estate for this mollusc lover. Waterbirds can survive and even thrive in harsh natural conditions.
Today, though, birds of rocky shores and sandy beaches must also cope with human-induced pressures, such as limited habitat availability, human population growth, and our increasing desire for recreation in formerly remote places. We now are learning how our actions can upset delicate balances in the life cycles of birds, particularly during the short window of time when birds must find a mate, build a nest, incubate eggs, and raise young. On the West Coast, this time window, March through September, coincides with our spring and summer recreation booms.
|Beach-nesting Snowy Plovers are vulnerable to disturbance. Photo by Dave Dixon.|
It is no coincidence that two birds dependent on West Coast beaches for nesting habitat are either federally endangered or threatened. The California Least Tern and Western Snowy Plover are highly adapted to the shifting sands of beaches and dunes: their cryptically colored eggs and flightless chicks match the beach sand, reducing predation. Sharing the beach with thousands of beachgoers, dogs, and off-road vehicles is a challenge for which they are not well equipped.
In 1999 and 2000, PRBO studied Western Snowy Plover chick survival on beaches in Point Reyes National Seashore (PRNS), California. We compared chick survival on weekends and holidays, when human recreation is highest, to that on weekdays. Significantly more chicks were lost on weekends and holidays in both years, suggesting that human recreation reduces Snowy Plover chick survival. Based on these findings, PRBO recommended using educational outreach and increased PRNS ranger presence on beaches, particularly during weekends and holidays. PRNS has implemented a unique outreach program in which rangers work closely with PRBO biologists. Using up-to-date information from biologists about sensitive chick-rearing areas, PRNS can focus outreach efforts to minimize disturbance on those high priority sites.
On the infamous rocky shores of Alcatraz Island, California, PRBO biologists have a unique challenge: to observe an assemblage of breeding waterbirds and the many humans that recreate and work on and around the island. The Brandt's Cormorant is the most numerous breeder on Alcatraz; in fact, the number of nesting pairs increased by 19% between 2001 and 2002, reaching the highest numbers ever recorded. During May 2002, while these sleek, iridescent, black seabirds were at their busiest incubating eggs and rearing chicks, 116,000 people toured Alcatraz! It's not surprising that humans and birds sometimes interact in such close quarters.
In the past three years, we documented disturbance to birds on and around Alcatraz at some of the highest levels on record. In 2002, nearby boat traffic caused one-third of all recorded disturbances. Surprisingly, kayaks are particularly potent vectors of human disturbance because of their silence: they can sneak up to birds and startle them more easily than can a loud motorboat. A single kayak that approaches too near a seabird colony can cause catastrophic breeding failure, flushing adult birds from nests and leaving eggs or chicks exposed to opportunistic predators and inclement weather. History has shown us that frequent or extreme disturbances on or around seabird colonies can cause complete abandonment of the breeding site.
On Alcatraz in 2002, PRBO biologists noted a rise in the percentage of disturbances that caused birds to flush from their nests. In response, Golden Gate National Recreation Area, which manages Alcatraz, is conducting educational outreach that targets groups using the peripheral waters. PRBO also promotes rigorous enforcement as well as clear signs and buoys around Alcatraz, marking a 100-meter buffer zone to help guide and inform kayakers, canoeists, and other boaters.
Thanks to cooperative efforts like these, human disturbance is gaining recognition as a major threat to bird populations. In many cases, however, we do not understand the causes and effects involved. Researchers, managers, and individuals must work hard to meet this conservation challenge.
PRBO recognizes the value of educational outreach to heighten public awareness. As automobile drivers, we abide by rules of the road every day to prevent injury to others. As bird populations decline and human recreation increases, it is more important than ever for each of us to uphold similarly mindful behavior when we enjoy the outdoors.