Mysteries Mark a Bumpy 2023 Plover Breeding Season at Point Reyes

By Wildlife Biologist Matt Lau, San Francisco Bay Area Network & Point Reyes National Seashore

Newly hatched and banded chicks hang out inside a hat before returning to the care of their parents. Bands identifying individual broods or plovers are key to helping biologists understand plover survival, movement, and more, so that they can recommend the smartest possible conservation actions.

NPS / Matt Lau

September 2023 - The western snowy plover breeding season in Point Reyes National Seashore ended on September 11th, when the last chicks of the season officially fledged. For the monitoring team and plovers alike, this season was a bumpy ride.

The nesting season started off strong, with a larger adult population size and a record number of simultaneously active nests. However, a string of adult plover disappearances and mysteriously low chick survival kept National Park Service and Point Blue Conservation Science biologists searching for answers. In the end, the season didn’t turn out quite as bad as we had feared over the summer. Nineteen snowy plover chicks survived to fledge and leave the care of their watchful fathers.

Female plover incubating eggs in the safety of an exclosure. Excolsures have been effective tools for protecting plover nests from predators. Adult plovers fit through the mesh, and can come and go as they please.

NPS / Matt Lau

In late March and early April, we found, and scrambled to monitor, a record-breaking 16 simultaneously active nests distributed across the Great Beach and Limantour Spit. It was clear the breeding population had also increased, partially because a high number of juveniles hatched in 2022 survived the winter and decided to stay local. We were able to locate nests and quickly deploy nest exclosures to protect them from predators.

However, several incubating adults went missing from a cluster of nests near North Beach parking lot. Most of the surviving non-incubating adults consequently abandoned the nests. We aren't quite sure what caused the disappearances, but one theory is that an avian predator targeted incubating plovers inside the exclosures, capturing them as they escaped. Just in case, we quickly removed exclosures on some active nests nearby and set up wildlife cameras on others farther down the beach to monitor for any predator activity. Cameras didn’t detect any threatening avian predators (I.e., raptors) that would be responsible for depredating adults, but we did capture images of common ravens visiting nest sites and circling the exclosures.

Nests that were able to survive to hatch faced further challenges such as dismal chick survival. Of 78 hatched chicks, 19 survived the 28 days to fledging for an overall chick survival rate of only 24%. While 19 fledged chicks is slightly above our 1996-2003 average of 17, the average chick survival rate has typically been much higher, at 41%. We don’t know what caused such low survival this year, especially because we did not detect an increase in predator (e.g., common raven) activity during our daytime surveys. With continued monitoring and further analysis or our data, perhaps patterns will emerge that hold clues.

A female plover affectionately known as the "Queen of Limantour" for her predictable presence breeding and wintering on Limantour Beach. Limantour was easily the most productive plover breeding site in Point Reyes this year.

NPS / Matt Lau

Despite these pitfalls, snowy plovers were able to pull through with some successes. We found 50 total nests throughout the park, the highest since 2018: eight on Kehoe Beach, 23 on the outer beach between Abbotts Lagoon and North Beach parking lot, seven within the Abbotts Lagoon restoration area, three south of North Beach parking lot, and nine on Limantour Spit. Overall park nest survival was normal at 58% (29 nests hatched). Limantour was easily the most productive site, where five of nine nests hatched, and seven chicks fledged (out of the 19 fledged parkwide).

We aren’t sure how the current El Nino weather patterns will affect breeding adult population numbers and juvenile return rates next season, but remain hopeful that plovers will return to Point Reyes beaches and continue their gradual, long-term upward trend.

For more information

• San Francisco Bay Area Network Western Snowy Plover Monitoring webpage
• Pacific Coast Science & Learning Center Western Snowy Plovers webpage
  • Western Snowy Plover Blog
• Point Reyes Western Snowy Plover webpage
• Contact Wildlife Biologist Matt Lau

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