We often see cormorants perched low above or near water with their wings spread. The common belief, endorsed many times in birding books and publications, is that cormorants have no oil gland.
All birds have an oil gland at the base of their tail, the uropygial gland. Using their bills, birds take oil and spread it over their feathers as maintenance. The oil has a waterproofing quality. If cormorants had no oil gland, they certainly would need to dry out. Soaking wet is not conducive to flight.
In a new and wonderful book, “Rare Encounters with Ordinary Birds,” author Lyanda Lynn Haupt discusses this erroneous view of cormorant biology, among many other delightfully interesting subjects.
This is not a biology book. This is not a facts-only book to supplement your field guides. This is a special collection of very well written stories and observations about the fascinating behaviors common birds offer if only we stop and watch.
Haupt watched cormorants, then did some research. She tells us that cormorants indeed have an oil gland. How could a diving bird, similar in behavior to loons and grebes and some duck species, evolve with such an obvious missing part?
Well, they didn’t. The gland is there, but cormorant feathers have evolved to be wettable.
Feathers lock together with edges of barbules and hooklets that zip up, providing protection from the elements. Cormorants’ feathers zip less tightly, allowing some water to enter. This gives the bird more weight, diminishing buoyancy, easing the effort of diving. For the same reason cormorant bones are more dense than bones of other birds.
The cormorant common to Minnesota, our much-aligned Double-crested Cormorant, does indeed spread it wings to dry. In the Pacific Northwest, were Haupt lives, Pelagic Cormorants do the wing-spread thing now and then, while Brandt’s Cormorant does it rarely.
Haupt’s book is driven by curiosity and an understanding that simply taking the time to look, even at or particularly at common birds, is a rewarding way to bird. There is more to it than meets the eye if you make the effort to look closely.
Other chapters in her book visit listing, Varied Thrushes, woodpeckers pounding on your house, making two bird species (or more!) from one, grouse, swifts, Winter Wren, sparrows, crows, and migration. She writes with grace, catching in these stories the same flashes of iridescence that sometimes burst from feathers.
I found this book at the Hennepin County Library. Published several years ago by Sasquastch Books in Seattle in soft-cover book with 191 pages the book is available from Amazon (as of Oct. 12) for $10.36. It is one of the best birding books I’ve read in a long time. It will make birding more interesting for you or a friend.