This resource I'm creating mostly as an investment in saving time on iNaturalist, to help explain why I have identified something as a cormorant pelvis. If you've stumbled across this independently, I hope it helps, though this isn't a through examination, rather a short and convenient overview.
Below are some key features of a cormorant pelvis from the dorsal view.
(A double crested cormorant, Phalacrocorax auritus, from https://virtual.imnh.iri.isu.edu/Osteo/View/Double_crested_Cormorant/570 )
1. In the circle, labled 1, is the feature I believe to be the most unique and distinct of any other cormorant pelvic feature. The anterior portion (I realize I misspelled this as "antierior" in my graphic, my apologies) is significantly flared, rounded to an almost semi circle shape. Other pelvises may have rounded anterior portions, but none others so dramatically as this, other than the anhinga, which I will explain how to different between cormorant and anhinga later on.
2. In the rectangle label 2, is emphasis on the very open space between the fused vertebra segments on the pelvis. These are the openings between the transvers processes of the vertebra, and I believe are called intervertebral foramina. Some pelvises look more solid, but here the openings are significant.
3. Outlined and labeled 3 is the posterior margin of the pelvis. Some pelvises are more flat, but this is more zigzagged. It also isn't particularly flared, and the whole pelvis leans on the narrow side.
However, a description and analysis of these features alone can sometimes be confusing without a proper context. How does someone know this pelvis has a flared anterior or narrow shape without seeing a normal anterior and wider shape? Comparison is key in identifying bones. So below I compare the cormorant pelvis with some other bird pelvises.
- The Canada Goose (Branta canadensis) has a rounded anterior, but not as circular as the cormorants. The posterior margin is much wider and more flat/less zigzagged.
- The Common Loon (Gavia immer) is extremely narrow, being some of the proportionally narrowest of bird pelvises along with grebes.
- The Great Blue Heron (Ardea herodias) pelvis is much more solid, lacking the pronounced spaces along the vertebra column.
- The anhinga (anhinga anhinga) pelvis also has a flared anterior portion, perhaps even more flared than the cormorant's. However, the proportions differ significantly from the cormorant. It's shorter and wider, with the top portion only marginally smaller than the bottom, where the cormorant is much longer and slenderer.
- The Glaucous Gull (Larus hyperboreus) pelvis is proportionally very short. The posterior margin form an almost trapezoidal shape, flaring out to be quite wide.
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