by Paul Donahue

15 February 2009

The group of birds known as shorebirds is comprised of the sandpipers, plovers and related birds that forage along our beaches, mudflats and rocky shores. Some species, like Western Snowy Plovers, Black Oystercatchers and Spotted Sandpipers, nest in our area, but most shorebirds are only winter visitors to the California coast, nesting elsewhere to the east and north. Many species of shorebirds travel north all the way to the tundra to lay their eggs and raise their young.

Unfortunately, the populations of many species of shorebirds, like those of so many other North American birds, are in decline. Some shorebird populations have dropped dramatically. Sanderlings, the little whitish sandpipers that chase the waves back and forth on sandy beaches, have experienced an 80% decline in their numbers since the early 1970’s.

There are at least several reasons for these declines in shorebird numbers - habitat loss, toxic pollution, global warming. In the case of some shorebirds, those that utilize sandy beaches, disturbance by humans and dogs has become a significant factor. The decline in Sanderling is almost certainly due to disturbance on sandy beaches during winter and migration periods.

Many of California’s sandy beaches, particularly those close to large urban areas, are heavily used by people and their dogs. As someone who spends countless hours watching shorebirds through binoculars, I am keenly aware of how easily shorebirds can be disturbed. Studies have shown that time spent by shorebirds foraging along beaches decreases in response to increasing and chronic disturbance from human activity. Other studies have shown that as pedestrian traffic increases on a beach, shorebird occurrence decreases.

While shorebirds may be disturbed by people in their habitat, they are REALLY disturbed by dogs. This is easy to observe on any day of the week. Sanderlings or Willets, another species regularly found on our beaches, may allow a string of walkers, joggers and surfers to pass by within 15 feet or so without showing undue alarm. However, as soon as a dog appears within a hundred yards of the birds, they freeze in their tracks, crane their necks up for a better view, and stand there waiting to see what the dog is going to do next. Shorebirds can’t tell if a dog is off-leash or not. If there is any indication that the dog is moving towards them, they’re gone in a flash of wings.

The real threat to the shorebirds from dogs is not that the dogs are going to catch and kill them. Dogs are way too slow to capture anything other than sick or injured shorebirds. The danger is in how the dogs affect the energy balance of the birds. Shorebirds, like most wild creatures, exist on a fairly tight energy budget. There is a small amount of slack built into the system, but not a lot. Anything that negatively impacts that energy balance threatens their physiological well-being.

Shorebirds eat mostly small invertebrates, up to and including mole crabs. Anyone who has spent much time walking along sandy beaches knows that the intertidal zone there is not exactly teeming with invertebrate life. Small creatures are there, to be sure, but they are mostly buried in the sand and difficult to find. Shorebirds need plenty of undisturbed time to locate these prey items they require to meet their energy needs.

All dogs on beaches disturb shorebirds. It has been well-documented scientifically that their mere presence is enough to stress the birds and impair their foraging efficiency. Beyond that, off-leash dogs that actually chase the birds are considerably worse. Not only do these dogs interrupt the foraging and resting time of the shorebirds, but in flying around to escape dogs, the birds burn off calories and expend large amounts of energy they can’t afford to spare.

Consequently, the populations of these shorebirds eventually suffer because the winter survival rate drops due to the poorer physiological condition of the birds. Beyond that, the nesting success of the birds in summer is negatively impacted by their poorer physiological condition through the previous winter. While dog owners may delight in watching their pet chasing shorebirds up and down the beach, they are doing considerable harm to these vulnerable birds.

Pacifica State Beach/Linda Mar Beach is a beach well used by shorebirds through the winter. It is regularly frequented by the endangered Western Snowy Plover as well as by several other species - Sanderling, Willet, Whimbrel, Marbled Godwit, and Black Oystercatcher. There is a leash law in effect for the beach which would help to protect these birds, but the Pacifica police are apparently either unwilling or unable to enforce this law. Walk the beach any time of the day, any day of the week, and you’ll see 10 or 20 off-leash dogs.

If you care about the survival of the beautiful and vulnerable shorebirds along our beaches, I urge you to keep your pet on a leash and, when possible, to avoid disturbing flocks of shorebirds you may encounter on your walks.

Paul Donahue
Pacifica, California
15 February 2009