The importance of oyster shells in the breeding success of western snowy plover

The Pacific Coast population of the western snowy plover (Anarhynchus nivosus nivosus) is a federally threatened species and is a California Species of Special Concern. Knowledge about their nest site selection requirements is important to this species’ management in the San Francisco Bay area. We measured the percentage of sand, percentage of crushed oyster shells, number of shells, and total shell surface area for 56 nests of western snowy plover at the California least tern (Sternula antillarum browni) colony in Hayward, California, USA, over a 14-year period (2008–2021). Using pairwise t-tests, we compared these measurements to those obtained from 56 randomly chosen non-nest sites. Results indicated that plovers select nest sites with greater oyster shell metrics than paired random sites. The contrast in the shell-related nest metrics (i.e., the difference between the nest site and the paired site) showed significant positive relationships with both hatching success and number of fledglings using linear regression analysis. These results, supporting federal species recovery, suggest that the western snowy plover may improve their nesting success through oyster shell enhancement, which may provide more camouflage for the eggs and chicks than locations with fewer shells.