Introduction and Background

The Pacific Coast population of the western snowy plover (Charadrius nivosus nivosus) was listed as threatened by the U.S. Fish and Wildlife Service (USFWS) in 1993. Point Blue Conservation Science (Point Blue) in partnership with USFWS, the California Department of Parks and Recreation (California State Parks) and other partners, has monitored nesting western snowy plovers (hereafter snowy plover or plover) in the Monterey Bay region since 1984. Beginning in the mid-1990s, this multi-agency working group has collaboratively planned, implemented, and assessed the effects of management actions taken to protect nesting plovers and meet the population target of 338 breeding plovers and the annual productivity target of 1.0 chicks fledged per breeding male identified in the federal Recovery Plan (USFWS 2007). Here we report on reproductive success and breeding population size of western snowy plovers in the Monterey Bay region in 2023 to assess the effect of management efforts intended to support population recovery.

Key Findings

The primary results of the 2023 breeding season are the following:

• The corrected window survey estimated that 314 western snowy plovers (Charadrius nivosus nivosus) nested in the Monterey Bay area in 2023.
• We documented 337 nesting attempts (297 active nests, 7 nests found when already inactive, and 33 broods of chicks from undetected nests).
• The apparent nest survival, or clutch hatch rate, was 62%.
• The nest survival estimated from the nest daily survival rate was 53%.
• A minimum of 502 chicks hatched.
• 320 chicks were banded and 127 (40%) of those survived to fledging age.
• An additional 112 unbanded chicks were confirmed to have fledged for a minimum number of 239 fledglings.
• The minimum estimate of chicks fledged per male was 1.44, which is above the 1.0 target needed for population stability.
• Breeding efficiency (BE) was greater than 0.2 (0.26), reiterating that there were likely more than 1.0 fledglings per male overall.
• 54% of all nest failures were attributed to predators.
  Of nest failure caused by predators, 27% was attributed to avian predators, 48% to mammalian predators, and 25% to unknown predators.
• Nest failures attributed to avian predators were almost entirely to species from the Corvidae family (corvids), but half of those failures occurred over a two-day window at one site (Zmudowski).
• The majority of nest failures attributed to mammals were either skunks (family Mephitidae) or species from the Canidae family (canids). More nest failures were attributed to them than to corvids.
• Nest success and fledge rates were higher in the South Bay than the North Bay. Also, a greater proportion of nest failures with a known cause were attributed to predators in the South Bay.
• At least one nest has been recorded at Laguna Creek beach in four of the past six years, including one nest in 2023. Monitoring effort has been lower here, so three nests had unknown fates, but two others were confirmed to have hatched.