Nest taphonomy of common terns (Sterna hirundo) on Poplar Island, Chesapeake Bay, Maryland

Abstract

Mesozoic non-avian theropod dinosaurs displayed a diverse range of egg types and clutch forms, suggesting a variety of nesting behaviours, some of which may be shared with birds. More accurate inferences of these behaviours require taphonomic studies of modern nesting sites. Here, we document common tern (Sterna hirundo) nesting sites on Poplar Island in Chesapeake Bay, Maryland. Nests were surveyed on multiple occasions, documenting nest composition, density and distribution, as well as eggshell concentration and orientation. Three colonies yielded 79 tern nests with 193 eggs. Twelve nests hatched, 7 were predated, 30 failed and the fates of 30 remain unknown. Abundant eggshells occurred at the centre of the nests. Concave-up eggshell in or on the nest surface characterised hatched and predated nests, whereas eggshell forced into the subsurface seemed to favour concave-down orientation and may reflect post-hatching extended use of the nest. Eggs buried deep within the nest materials and/or substrate suggest adult abandonment. Quantitative data on eggshell orientation and observations regarding controls on nest distribution, egg predation and incorporation of intact eggs into the substrate at modern nesting sites provide physical guidelines for the improved interpretation of fossil nesting localities.

Keywords::

• dinosaur
• tern
• nest
• taphonomy
• eggshell

Acknowledgements

We thank P. McGowen and C. Guy at the United States Fish and Wildlife Chesapeake Bay Field Office for their support and boat rides to Poplar Island; M. Erwin of the USGS Patuxent Wildlife Research Center for allowing P. Wang to participate in the common tern population survey on Poplar Island and for supplementing nest outcome data. We appreciate the support of P. Wang, L. Wang (for statistical assistance), N. Wang (for mapping assistance) and P. Hepp (for field assistance). We also acknowledge support from the Masters of Science in Science Education (MSSE) staff including P. Taylor, D. Patterson and L. Rugemer. Research was in part supported by NSF grant #0847777 (EAR) to D. Varricchio.