At least two snowy plover nests have unexpectedly appeared on Limantour Beach. Though that could signal an exciting happy comeback—the federally threatened birds have been absent from the beach since 2000—Point Reyes National Seashore biologist Dave Press has a concern: the eggs may hatch this weekend. The park has erected fencing around the nests, which are known as “scrapes” and are literally depressions in the sand, and there will be signs and docents present over the weekend. Leased dogs are allowed on the section of beach, but Mr. Press stressed the vulnerability of the chicks. How long will they remain there after hatching? John Dell’Osso, spokesman for the seashore, said plovers are precocious, moving around just as soon as they’re born. Sometimes male plovers, which guard the nests, decide to move chicks “down the beach” to a quieter locale. “That’s even more worrisome!” Mr. Dell’Osso said. More than a dozen plover nests were counted this year between North Beach and Kehoe Beach. They have never before been documented in their new location at Limantour.