As a newbie observer of birds, one aspect of their lifestyle (besides flying of course) that really amazes me is how they accomplish so much with no hands. Like these Canada Geese, grooming quietly in the corner of the bay, seeing to their feathers in a variety of graceful positions.
Obviously birds have made the tradeoff, with wings giving them a huge lifestyle advantage in getting food, escaping predators and all the rest. But wings are so specialized they aren't used for much besides flying (or diving for some). No hands means finding other ways to gather and manipulate food, drink water, pick things up, build nests, defend themselves. And considering the crucial importance of their feathers, for grooming.
One day I saw a goose reach around and stretch all the way back to its tail, biting at a certain spot.
Doing a little reading, I discovered it was going at its preen gland, or more properly speaking, its uropygial gland. Turns out almost all birds have one in that spot, and that it is essential in caring for their feathers. Veteran Dawn Chorusters may already know about who uses it, and how, and for what else, but I'll share a bit about what I've discovered along with my pictures of local birds.
I was particularly intrigued by how various birds physically access the preen gland. It seems awkward even for the goose, with its long neck. I began paying attention to other birds to see how they managed.
(All photos by me. In Lightbox...click to enlarge)
Except for just a few - the Kiwis, Emus, Ostriches, Rheas, Cassowaries and Bustards, some Pigeons and Doves, and the Amazon parrots - all birds have a preen gland. Even in these birds without one it is vestigial and evident embryologically. The gland opens at the base of the tail, releasing a greasy waxy mixture that birds capture on their beaks, sometimes squeezing the nub, as the goose was, to extract the preen oil.
Preen oil is a mixture. Its composition varies from one bird group to the next, and throughout the year. For example, the kind of fatty acids of the wax esters that many Anseriformes (geese and ducks) have are multibranched monoesters while the Galliformes' have straight chain diesters. That's enough of chemistry, but it tells me that preen oil composition is another characteristic distinguishing bird families.
This hen turkey's preen oil has a different greasiness than the goose's. Her chicks are quite young in this photo from last summer, but I notice they are actively using their preen glands already.
Trumpeter Swans have nice long necks too that easily reach the gland, as well as the rest of their bodies. Birds spread the preen oil onto all their feathers.
A gull's neck is not particularly long, but it has no trouble stretching its beak all the way back to the preen gland. An indication of the importance of neck flexibility is the fact that birds have 11-25 neck vertebrae, as compared to the 7 in mammals.
Once the beak is smeared with preen oil, the gull pulls every feather through it. The oil keeps the feathers in good condition, healthy and flexible, with properly interlocked barbules. If flying wasn't enough reason to maintain the integrity of feathers, there are 22 others ;-)
Preening feathers on its head is accomplished by a combination of feet and rubbing against its oiled back. That's flexibility!
Most of the birds I observe are along the shore or in the water. Preening while floating is no problem.
Red Breasted Mergansers:
Being immersed in water presents a challenge in dealing with belly feathers though. This female Bluebill rolls partway over to deal with those. Looks awkward, but like the Buffleheads, I've never seen these onshore, grooming or otherwise. They manage fine while floating.
Dabbling ducks are comfortable on shore, but even they seem to preen more often while floating in the water. This female Gadwall giving me the stinkeye is likely expressing the reason. Preening diverts attention from possible predators, so being offshore lessens the chances of predation by dogs, people, etc. No matter where they are, birds seem to take frequent breaks in their preening to check out the surroundings.
Flocking birds can depend on compadres to alert them, like this Pintail:
What do the birds with no preen oil do for feather maintenance? Powder down, the tiny fine pieces continually broken off this kind of down feather, serves the same purpose. Some birds, like herons and pigeons, have both preen oil and powder down.
A misperception out there is that preen oil waterproofs feathers. While it is a waxy substance, what the preen oil actually does is to keep the feathers in good enough condition so their structure and arrangement maintains waterproofing. This study determined that "no correlation was found between the size of the gland and the aquatic/terrestrial nature of the species." In other words, aquatic birds don't have more preen oil. It has a detailed description of the anatomy and physiology of the preen gland, with some interesting discussion of other possible functions of preen oil. Some I've read about are smelliness to deter predators (Hoopoes), attraction of mates (chickens), and sibling recognition (waxwings).
Some information sites still state that cormorants and anhingas don't have preen oil, and that their feathers aren't waterproof, which requires them to spread their wings in the sun to dry. Not so. These Pelagic Cormorants at the Anacortes ferry dock preen frequently. The pics were taken during breeding season last summer, with the later chicks still downy, and the adults still in their gorgeous breeding colors.
A juvenile Pelagic shows off its preen gland nub:
While the feathers of Cormorants and Anhingas are waterproof, their wings are wettable, allowing water to stick. This makes them less buoyant so diving is easier. Spreading their wings in the sun helps dry them off. It also warms them up. Other birds use the spreadwing posture for thermoregulation too, like Turkey Vultures.
To close, I'm sharing some preening photos of my local Black Oystercatchers, starting with a dollop of preen oil from the gland opening by the tail. They groom with a pragmatic economy of motion that is also a graceful ballet.
Opening his wings to resettle them, we can appreciate just how many feathers there are, each needing individual attention. The number varies, from 940 in a hummingbird to 25,216 for a swan.
No wonder birds spend so much time preening every day. And no wonder oil spills are so destructive to them. Not only are their wings and feathers covered, ruining their ability to function, but in trying get clean, they inevitably ingest the poisonous petroleum since their only way of cleaning themselves is with their mouths. The number of affected ducks, herons and shorebirds in Galveston bay is in the hundreds already. Watching birds, I get the sense they are involved in survival activities most of their time even on a good day. A lot of birds won't make it there. The sadness and disgust we feel about the fate of these innocent creatures should inspire us fight for changes to that industry.
As you can see, the birds I observe each day most often are water birds, whose preening takes place out in the open. Do you have photos of songbirds and others whose preening is more private? Thoughts and observations of birds are welcome.
I'm not a morning person (arggh, how can I be a birder then?) but I'm publishing this diary at the usual hour, 6 AM Pacific Time. I'll catch up with comments later on :)