Taphonomic assessment of material generated by an Arboreal Nesting Colony of Great Blue Herons (Ardea herodias)

ABSTRACT

Reports on nesting debris generated by great blue heron (Ardea herodias), arboreal nesting birds with ‘semi-altricial’ young, are limited. In this study, surface and subsurface sampling were conducted in 2012 and 2013 in a heronry near the Missouri River in Montana, including bi-weekly collections in 2013 documenting accumulations over the breeding season. Disarticulated juvenile heron bones with lesser numbers of microvertebrates (fish and small mammals) and invertebrates (crayfish and snails) dominated the assemblage beneath the nests. Eggshell on the surface was present but uncommon (0.85 eggshells/m²) with eggshell orientation varying both by location and fragment size. Eggshell surveys differed with respect to sampled trees and sampling time, but generally favoured concave-up orientation whereas the early season small eggshell survey further from sampled trees favoured concave down. Shallow (10 cm deep) excavation revealed a subsurface assemblage very similar to that on the surface but favouring more resistant elements. Hence, the subsurface assemblage was nearly devoid of eggshell, with a lower representation of invertebrates and fragile bone, but an excess of heron hindlimbs. Our study demonstrates that arboreal nesting sites have the potential for long-term preservation and provides information useful for recognition and reconstruction of arboreal nesting sites from the fossil record.

KEYWORDS:

• Ardea herodias
• taphonomy
• arboreal nests
• wing-to-leg ratio
• eggshell
• pellet

Acknowledgments

This work was supported in part by the National Science Foundation grant #0847777 (EAR) to DJV and made possible through several field courses at Montana State University such as the Dinosaur Paleontology of Hell Creek Formation (2011), the Advanced Paleontology for Teachers (2012), the Research Experience for Teachers at Egg Mountain, and the 2012 Field Paleontology Class (GEO 419). We are grateful for the permission and continued support to conduct this research over two breeding seasons from the owners of the heronry. We are indebted to Frankie Jackson for her time and assistance with the design and manuscript edits contributing to this paper. We also thank Carter McGrath and Brian Custer for their time, comments, and extensive manuscript review. We appreciate the field assistance received from students in the 2012 GEO 419 class, Carter McGrath, Chuck Merja, Cathy Powell, and Christine Whaley. We also thank Ken Scow and Nancy Scow for their early manuscript edits and Michael Chapman for his photography assistance.

Disclosure Statement

No potential conflict of interest was reported by the authors.

Supplementary Material

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Additional information

Funding

This work was supported by the National Science Foundation [0847777].