Among the many diseases that afflict wild birds, there is avian flu, which made national news when it began decimating flocks of domestic turkeys and chickens. This very pathogenic strain (known as H5N1) of the avian flu virus emerged from Asia in the 1990s and quickly spread around the world.
It is known to occur in over a hundred species of wild birds. It caused outbreaks in 2004-2006, and as of early 2022, it was officially reported in geese and especially eagles in Alaska. This virus has seriously damaged some wild bird populations: California condors, pelicans in South America, skuas in Scotland, for example. Raptors are said to be very sensitive to flu virus, and waterfowl often carry and transmit it. Songbirds are (so far) less affected. Bird flu is also known to affect mammals of various species.
The virus is shed in saliva, mucus, and feces of infected birds. It is transmitted to other birds by direct body contact, inhalation of air-borne cells, and especially by ingestion (by eating infected birds or carcasses or incidentally ingesting fecal material (such as that dispersed in marshes and ponds).
The bird flu virus affects respiratory and gastrointestinal tracts. Some common strains have relatively low pathogenicity. The very pathogenic strain can cause lack of energy and loss of appetite, diarrhea, nasal discharge, coughing, sneezing, lack of coordination, tremors, swelling and discoloration of featherless parts, decreased egg production, and sudden death.
Less widely known is another nasty virus called avian pox; it’s in the same taxonomic family as smallpox and monkeypox. It can have several different effects; if it becomes (uncommonly) systemic, it can lead to anorexia and depression, or it might invade the mucus membranes and upper respiratory tract, causing respiratory distress. But the best known and most easily visible to observers is the eruption of raised lesions (or “poxes”) on the bare skin of the face, legs, and feet. The external lesions can last as long as a month, sometimes causing blindness, beak deformations, and loss of feet and toes. An afflicted bird can recover and develop antibodies, although the lesions may leave some scars, but a seriously debilitated bird may starve and die. The lesions also create open wounds that bacteria can enter, leading to secondary infections, and the immune system may be suppressed.
Avian pox contributed to the extinction of several bird species in Hawaii. Cases of avian pox in various species here have been reported here in the past, especially in crows and ravens. This year (September 2023) photographers have recorded the pox in crows at The National Shrine of Saint Thérèse and a raven at Eagle Beach. Sadly, the raven seemed to have a really bad case, apparently almost blind and having difficulty feeding (https://youtu.be/eA1mJbTJY5s, thanks to Bob Armstrong for the video). Outlook: not good.
An infected bird in captivity may receive topical treatment of the lesions with an iodine solution such as betadine. The lesions also may be debrided and dosed with antibacterial medicines. And the diet might be supplemented with vitamins and extra fluids to help healing and reinforce the immune system. Local rescuers were able to heal and eventually release an eagle that was cared for in this way.
The virus often enters through openings in the skin, sometimes via a bite of an insect (mosquito, fly, flea) that previously fed on an infected bird. But the virus can also enter from an infected perch or bird feeder through existing skin abrasions. And it can enter a bird via inhalation or ingestion. So it has many ways to get around. But where does it live in the meantime? I’ve (so far) found no information about where it lives in between detectably infecting birds.
Avian botulism can be another serious problem, caused by a Clostridium bacterium that produces a potent neurotoxin. That toxin causes failure of muscles involved with walking or flying, respiratory and cardiac paralysis, and death. The bacterium is widely distributed in soils and water, and can be incidentally consumed by animals that filter their food from sediments or water. Shoveler ducks are good filter-feeders and may take in the bacteria while they feed. Other birds, such as loons and gulls, eat fish and invertebrates that can be infected and pass the bacteria on to the predators. Maggots feeding on dead fish or other animals are a choice food for lots of birds, but those maggots can accumulate the bacteria or the toxins and pass them on to maggot-eaters (this species of Clostridium does not affect mammals, who get botulism from related bacteria). The abundance of botulism bacteria is thought to increase in warm waters with low oxygen, increasing the likelihood of transmission to invertebrates and birds. Botulism has caused or contributed to many avian mortality events around the world. The first recorded botulism outbreak in Alaska occurred in 2021, when there was a considerable die-off of kittiwakes, showing the characteristic symptoms, on Middleton Island.
Another serious source of avian disability and mortality comes from pesticides. Some are acutely toxic, while others have less immediate detrimental effects. Pesticides are applied to both terrestrial and aquatic environments, and run-off from treated lands to water distributes the pesticides more widely. The chemistry of these pesticides and their effects would fill books, so here I’ll just note that pesticides taken up by the “pests” (insects, rodents, etc.) are passed on to avian consumers, with serious negative effects. So birds that eat worms or bugs or fish from pesticide-treated areas are exposed to the dangerous chemicals, with documented cases of reproductive failure, morbidity, and die-offs. Also, seeds treated with pesticides can pass on those toxins to seed-eating consumers. These problems could be avoided by choosing and applying pesticides with great care.
I haven’t space to discuss the documented cases of avian mortality resulting from toxic run-off from mining activities. But that has been a serious problem in some regions and is a continuing threat wherever mining activities drain into rivers and lakes, including several river drainages in Southeast.
• Mary F. Willson is a retired professor of ecology. “On The Trails” appears every Wednesday in the Juneau Empire.