Seasonal predation by migratory shorebirds recorded in shells of lingulid brachiopods from Baja California, Mexico

Repair scars attributed to shorebirds are very frequent in intertidal populations of Glottidia palmeri (Lingulidae, Brachiopoda) from the Gulf of California. The multimodal distribution of the scars along the anterior-posterior axis of the brachiopod shells suggests the existence of strong temporal variation in the intensity of predation. Bootstrap analyses of the scar distributions, size-frequency population data, and growth ring data all indicate that the scars are seasonal and originated in the late fall and/or winter months. The scars record predation by migratory shorebirds that have wintering grounds in Baja California. The anterior-posterior distributions of scars can offer insights into seasonal variation in predation on marine benthos. Also, because seasonal repair scars represent a periodic signal, they may estimate the longevity and growth rates in prey and offer a "sclerochronological clock" analogous to oxygen isotopes or growth rings. The approach proposed here may be applicable also to the fossil record of some shelly organisms.