A lot of people have asked me about the brown pelican carcasses strewn around the edges of Abbotts Lagoon this fall, so I thought I’d offer my observations of the wildlife dynamics out there. First, the pelicans were predated by river otters. As far as I know, the increase in carcasses is not due to environmental disaster. It is natural—a sign of health and abundance along the coast. Granted, with the cumulative effects of over-hunting, overgrazing and over-logging, and with anthropogenic climate change, very little can be truly called natural anymore. Yet given half a chance, nature persists and thrives. River otters, which have made a resounding comeback in the San Francisco Bay Area, are an example. Population recovery is a complex process, and new efforts to protect wildlife can take an erratic path with unexpected results.
What I see at Abbotts Lagoon is a learning curve: As dynamics shift, the otters are adapting. With each passing year, the otter population has become more stable and permanent, and the families are bigger. As they grow more familiar with the territory, they become better hunters of more diverse prey. Fish is far from all they eat. We often hear them crunching up small crustaceans in the pennywort and cattails along the shorelines, and on their extensive overland travels they commonly catch small rodents, birds and reptiles. The Abbotts otters frequently commute north to Kehoe Creek and back, traveling through the upper dunes or along the surf line. They will even swim out into the surf to catch fish and surf scoters. They hunt ducks and cormorants in the lagoons—and the occasional pelican.
In our climate zone, late fall before the rains arrive can be a hard time to survive for many animals. Forage is scant, rodents decline, and in the lagoons the larger freshwater fish decline, especially after a summer of predation by growing numbers of otters. Food is scarce. Nature solves this problem for the otters with the earliest arrival of migratory waterfowl. Typically, at Abbotts Lagoon, cormorants begin to leave in the fall, just as the first migratory coots arrive, well before the rains bring the true duck migrations. The coots serve as a transition food for the coyotes, bobcats and otters. Once the rains arrive and the rodents increase, the land predators ease up on the coots and the otters begin preying on the newly arriving ducks.
Another early arriver is the brown pelican. Though not a true migrator, brown pelicans move up and down the coast with the seasons and weather patterns. Local oceanic upwelling can increase sea fish populations and pelicans will follow. At Abbotts they tend to flock up in late summer before the ducks arrive.
This year, though, has been a little different. After a very dry winter, the heavy rains last May filled the lakes and ponds and came at a perfect time to stimulate a surprisingly heavy crop of grasses and forbs throughout West Marin. This, in turn, seems to have supported one of the largest rodent populations in years, particularly mice and gophers. Good news for the bobcats and coyotes, which are also increasing. For the otters, the big shift came with the late-summer pelican arrival. As pelican numbers have increased, otters have gotten better at hunting them. Their typical strategy with ducks and cormorants is to come up from underneath, grab them with their teeth and pull them underwater. The otters were doing much the same with the occasional pelican that would swim and hunt in the deeper waters of the upper lagoon. This must be a greater challenge with a bird as large as a pelican, but the otters have perfected the art, possibly working two on one. A surprise grab from underneath, a swift bite through the trachea, hold on tight and the job is done. The result is a larger number of carcasses along the shores.
The pelicans may be learning, too. They began avoiding the upper lagoon and shifted to the south shores of the lower lagoon, where low water levels provide extensive shallow sandbars to roost on overnight—and more privacy from the ever-increasing presence of humans. If an otter must swim up under a pelican to hunt it, shallow water is clearly a safer place, while still keeping the pelican at a distance from coyotes patrolling the shoreline. But with such large flocks this year (I recently counted over 1,000 of them, roosted in a long line along the shore), space is limited and some pelicans are forced to float out in deeper water, where they are more vulnerable to otters.
The coyotes, always quick to adapt, are also learning. When the otters pull a pelican close to shore to begin feeding, a coyote will wade out to steal the big bird and then drag the carcass up into the dunes. There it can dine with more privacy and safety, albeit with the company of ravens and vultures, which are also cottoning on to the new game in the old dance.
This whole story has been a great lesson in the dynamics of nature, whose intricately woven fabric adjusts and responds to ever-changing conditions. While some folks may be shocked to learn that the otter, this cute icon of wild animals, is such a fierce predator, it is actually a lesson in the intelligence of wildlife and a hint at the enormous resilience built into each species.
Richard Vacha is a longtime nature lover and animal tracker, author of “The Heart of Tracking” and founder of the Point Reyes Tracking School. He lives in Point Reyes Station.