For the Birds – Long-billed Bird Syndrome
A bird’s beak is a remarkable structure. The shape of the beak tells us much about the type of food a bird eats. It’s obvious that a hawk’s bill is adapted for tearing, that a heron’s bill is adapted for spearing and that a finch’s bill is adapted for crushing seeds.
The lower jaw or mandible of a bird is composed of a pair of dentary bones that fuse at the tip. The upper jaw or maxilla is made up of nasal bones near the base and premaxillary bones at the tip.
Unlike the upper jaws of mammals (including us) that are fused to the skull, the upper jaw of a bird attaches to the skull at a flexible hinge. When a bird opens its mouth, the lower jaw moves downward and the upper jaw moves upward relative to the skull. Birds can therefore open their mouths wider than a mammal.
The beak of a bird is covered by a sheath called the rhamphotheca. The sheath is made of keratin, the same material that makes your fingernails. In most birds, this sheath is hard but in waterfowl and shorebirds the sheath is soft and leathery.
As a bird feeds, abrasion causes the sheath to wear away at the tip. The skin overlying the bones of the maxilla and mandible continuously lays down new keratin to replace the lost material.
It’s interesting to note that the beak length of some birds changes from winter to summer. As an example, House Sparrow beaks are longer in the summer. During the summer, House Sparrows eat softer foods compared to the winter when hard seeds are the staple of the diet. Feeding on the hard seeds breaks down the sheath more quickly and the winter bill length therefore is slightly reduced.
Birds kept as pets often are not given hard enough foods to allow the birds to wear down the tips of their bill. That is why parakeet owners provide their birds with cuttlebone.
In the past ten years, a serious and even grotesque condition called long-billed bird syndrome has been documented. Bud Anderson, a hawk biologist at the Falcon Research Group in Bellingham, Washington noted a Red-tailed Hawk in 1996 with an overgrown beak. Since then, Anderson has recorded 86 hawks with deformed bills; all but nine were Red-tailed Hawks.
The condition is caused by hypergrowth of the sheath. The hypergrowth can take a number of forms but the end result is that the function of the bill is severely compromised. Examples can be seen at: http://www.frg.org/frg/lb_syndrome.html
The condition is lethal without intervention. Hawks with the condition are underweight because they cannot process prey with their bill. They are usually plagued with feather lice, presumably because their deformed bill does not allow them to preen.
Long-billed hawks are easily captured. They quickly come to a prey lure because they are desperately hungry. A rehabilitator can remove the excess sheath and release the bird after it recovers its weight.
The long-billed hawk syndrome has mostly been documented along the west coast of North America, from San Jose north to Richmond, British Columbia.
However, the long-billed syndrome is not restricted to hawks. Recently, a biologist near Anchorage, Alaska documented over a thousand Black-capped Chickadees with overgrown bills. Biologists in Montana have found the syndrome in Red-winged Blackbirds.
Julie Craves, a Michigan bird bander, and Colleen Handel, a biologist with the U. S. Geological Survey, have compiled records of the long-billed syndrome in North America. They found records of overgrown bills in over 110 species of birds, mostly songbirds. Records of this condition have been reported from places as far-flung as Florida, Baja California, Maine and several Canadian provinces.
At this point, the cause of the syndrome is not known. We do not know if the condition results from the same cause in all the species that have been reported to have these deformed bills.
For hawks, the condition is found in both young and adult birds. Blood tests of afflicted hawks show that white blood cell counts are normal; one would expect elevated counts if the birds harbored some of disease organism. Veterinarians tested affected birds for thyroid disorders and beak and feather disease, two diseases that cause deformed growth in parrot beaks. The tests for both diseases were negative.
Currently, veterinarians are looking for pathology of the cells that produce the keratin sheath in long-billed birds. Perhaps some clues to the cause of the syndrome will be forthcoming.
You can help by reporting any birds you see that have long bills to Bud Anderson at: email@example.com
[Originally published on September 17, 2006]