Seeing a bald bird can be a shock, especially if it is not a species birders typically expect to have a bald head or large unfeathered patches. There are many reasons birds may be bald, however, and understanding bird baldness gives birders greater insight into the value and purpose of birds' plumage.
Naturally Bald Plumage
Some birds naturally have bald patches in their plumage. Some of these patches are protective, such as the bald heads and necks of many carrion eaters like vultures where feathers would otherwise become infested with bacteria. Bald patches may also be related to courtship and mating, such as bare skin that can change color with sexual readiness or to attract a mate, like the lores of a great egret. The size, shape, and color of bald patches will vary, and may be just around the face or could cover the entire head, face, and neck. Bald patches may include eye rings or distinct wattles as well, like the wild turkey's snood.
Birds with naturally bald plumage include:
- All vultures and condors
- Wild turkeys, ocellated turkeys, and many large pheasants
- Many storks and ibises
- Some herons, egrets, and cranes
- Different hornbill species
- Emu, ostriches, and cassowaries
- Muscovy duck
- Vulturine guineafowl
- Montezuma oropendola
- Bald parrot
- Bare-faced bulbul
- White-necked picathartes and gray-necked picathartes
Many birds are bald when they first hatch, or have just a few fluffy down feathers that may not completely cover their exposed skin. These altricial birds will rapidly develop thicker down plumage, but they require intensive care by their parents to regulate their body temperature until their feathers are more developed. Within 2-3 weeks, most small altricial hatchlings begin to develop their more mature adult feathers, though larger species such as raptors may not fully develop their adult feathers for several more weeks. While the plumage coloration and markings of juvenile birds may be different than adults, they can no longer be considered bald.
Baby birds that are hatched bald include nearly all passerines, raptors, hummingbirds, swallows, parrots, woodpeckers, and many other birds.
There are unusual circumstances that can lead to baldness in nearly any bird species. While these may not be ideal conditions for temporarily bald birds, most birds do recover and regain their plumage.
- Molting: Birds generally molt in subtle, specific patterns that do not result in bald patches, but some birds develop more abrupt molting cycles that can create temporary baldness. This happens frequently in northern cardinals, blue jays, and common grackles. It is not unusual to see one of these birds with a partially or completely bald head in late summer or fall as they complete their seasonal molts. Most often, this aberration is seen with juvenile birds molting into their first fully adult plumage, but if a young bird molts in this way, it may continue the pattern each year. The feathers usually regrow within 7-10 days.
- Mites: Different types of mites can infest a bird's feathers, causing feather loss and plumage damage that can result in baldness or bare patches. Birds will typically preen away these parasites or may use sunning or dusting to discourage mites, but if the infestation is bad enough baldness can occur. This is especially visible on the head, where birds are less effective at preening and damage to smaller, more delicate feathers can be more extensive.
- Injury: If a bird has struggled with a predator but managed to escape, it may have some bald patches where the feathers were ripped away in the encounter. This baldness may have a scraggly appearance and surrounding feathers may be damaged, and tailless birds are often predator survivors. If the feather shafts have been severely damaged, it may take a long time for the feathers to regrow or some baldness may be permanent. Fire-related injuries may also cause baldness where plumage has been burned away.
- Illness: Diseased birds may lose feathers resulting in some temporary baldness. Another symptom of some diseases can be swollen skin patches or blister-like growths that protrude through the plumage and give the appearance of bald patches. When birds are ill to the point of showing baldness the sickness usually shows other symptoms as well, and if the birds recover the baldness will disappear.
- Poor Nutrition: Feathers are composed of keratin and require large amounts of protein for proper growth. If birds do not receive adequate nutrition, poor feather growth and baldness may appear. Few studies have been done on the effect of nutrition and overall feather development, however, and additional research is needed to determine if poor nutrition can result in bird baldness.
Not Really Bald
Some birds may be called "bald" but really aren't. The bald eagle, for example, is so named because of its fully white head that contrasts with its brown body feathers, while the American wigeon has the nickname baldpate because of its white crown that can look like a bald head. The white-crowned pigeon is also called the baldpate occasionally, also for its white head that resembles baldness. All of these birds, however, are fully feathered and have no true bald patches.
With nearly 10,000 bird species in the world, birds' plumage is highly varied, and bald birds can be fascinating. Understanding the natural and temporary causes of baldness can help birders better understand plumage and appreciate the diversity of having or not having feathers.