Western snowy plovers, a threatened shorebird whose population the Point Reyes National Seashore has spent years trying to foster on sands from North Beach to Abbotts Lagoon, suffered a high rate of nest failure this year. Thirty of 45 nests that cradled eggs either never hatched, or produced chicks that died within the first month of life.
New wildlife cameras set up at a few breeding sites found surprisingly tenacious ravens lurking nearby, pointing to a possible culprit for the failures. Despite the losses, the total number of successful nests is the same as last year (when 15 of 21 nests yielded fledglings), the highest counts since 2007. And six of this year’s fledglings came from dunes around Abbotts Lagoon that the park began restoring in 2011 by pulling out non-native European beachgrass—the first time any chicks have fledged in the restored area since that project began.
(There were 14 total nests in the restored area this year; from 2011 to 2013, roughly one nest per year was built, but none hatched chicks.)
Dave Press, a wildlife ecologist for the seashore, said the park takes measures to try to protect the plovers from predators, but figuring out how best to defend the nests is complicated.
The park has in years past built exclosures, or cages, around all nests to protect them from predators like foxes or ravens. Last year, the park assembled exclosures around just a portion of the nests because the structures also attracted hungry animals, which learned that tasty chicks might wander outside the cages once eggs hatched.
Sometimes, when predators lurk incessantly at the borders of exclosures, the breeding plovers “just freak out and leave,” Mr. Press said.
But this year the park again placed exclosures around most nests, hoping to avoid the widespread failures of 2013.
Though Mr. Press said it wasn’t possible to know exactly what spurred the plover’s nesting plight, the park did combine their own observations with a few new wildlife cameras; usually, Mr. Press said, “the only thing we have to go on are tracks in the sand.”
The cameras didn’t cover the entire nesting area, but footage found ravens eyeing eggs and chicks, targeting nests as opposed to simply flying by and fortuitously spying a potential meal. Though ravens are a known predator, their persistence was startling. “The intensity of visitation by ravens to nests was more than I expected, based on the cameras. One morning, there were four separate visits by a pair of ravens. Four times in one morning walking right up to an exclosure…So that’s pretty intense if you’re trying to get those eggs to hatch,” he said.