Smaller Cages, Safer Nests: Point Reyes Tries Mini-Exclosures for Snowy Plovers

By Matt Lau, wildlife biologist, San Francisco Bay Area Network western snowy plover monitoring program, July 2022.

Banded western snowy plover chicks. By June 30, biologists had found 29 nests on Point Reyes beaches; 15 had hatched. NPS / Matt Lau.

A good season so far

The western snowy plover nests at Point Reyes National Seashore from March to early or mid-September. By June 30, 2022, biologists from the San Francisco Bay Area Network and Point Blue Conservation Science had found 29 nests: 15 hatched, 8 failed and 6 still active.

Why so many: more of 2021's juveniles than usual survived the winter, and many 2021 breeders returned. At least eight plovers hatched on park beaches in 2021 were nesting, or showing interest, in 2022. About 35–40 plovers were breeding — the high end for recent years.

A new kind of exclosure

Exclosures — wire cages over a nest — keep predators out while the plovers come and go. In 2022 the team began using mini-exclosures, 25% the size of the old large, round ones:

• Less conspicuous to predators and visitors;
• Easier escape for the incubating adult when a predator or disturbance comes;
• More portable, so newly found nests are protected faster.

So far, the new design has boosted nest success.

One of the large, circular exclosures used in the past. NPS / Matt Lau.

A new mini-exclosure. NPS / Matt Lau.

Plovers and a warming climate

Network biologists and Point Blue researchers also studied how plovers may respond to climate change:

• Warmer temperatures will likely raise predation risk at nests, on top of habitat loss from sea-level rise.
• Chick survival, by contrast, showed signs of benefiting.
• Exclosures matter even more, to offset warming's indirect effects.

More in Park Science: "Western Snowy Plovers Could Face Multiple Threats from Climate Change" (Lau, 2022). See also the network's snowy plover monitoring page and the Western Snowy Plover Blog.

Sources

Based on "Biologists Test New Nest Exclosure Design for 2022 Snowy Plover Breeding Season," by Matt Lau, San Francisco Bay Area Nature & Science Blog, National Park Service; a work of the United States government in the public domain.