Parasitic Diseases of Wild Birds

Written by jasey kelly
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Parasitic Diseases of Wild Birds
Wild birds play host to a variety of parasites. (wild bird image by Gail Ranney from

Wild birds are prone to a variety of parasites, both internal and external. While some may cause death, the host bird may never notice others. Because of the vast variety in parasite species, being able to identify the particular host for each case is important in determining the effect of the parasite. Parasites may also cause die-offs, which are sometimes detrimental to local bird populations.


Flukes, or trematodes, are often the result of waterfowl feeding on infected mollusks. The flukes can also occur in other wild birds, particularly those that have fed upon dragonflies and other aquatic-loving insects. The tiny flukes have a somewhat complex life cycle. Once the bird is infected, trematode eggs are released in the stool where the embryos develop in the water. There is a first and second intermediate host, often snails or mollusks. The trematodes leave the first host, then develop more on or in the second intermediate host. The second host, in turn, is eaten by the bird and the life cycle begins again.

Some of these trematodes produce die-offs within wild bird populations, normally during late summer or early fall. In the United States, most reports occur in the Northeast or North-Central regions.


Several species of tapeworm infect wild birds. Tapeworms primarily invade the intestinal tract of birds, some causing death and others seeming to show no signs within the bird. The tapeworm life cycle requires an intermediate host. Common intermediate hosts include ants, beetles, stable flies, leeches and slugs. Aside from the intestines, different species of tapeworms can invade the gizzard or ureter.


Roundworms are known to infect many wild birds. Most species prefer to live in the gastrointestinal tract, while some may inhabit the trachea or eye of their chosen host. Like many other parasites, roundworms require an intermediate host prior to the final bird host. Common intermediate hosts for roundworms include beetles, sowbugs, cockroaches and earwigs, among others.


Ectoparasites are parasites that are found on the exterior of the bird, in contrast to internal parasites. Ectoparasites are known to cause disease and sometimes death in their hosts. Ticks, for example, can cause anaemia, weight loss and other symptoms and disease on a bird. Tick paralysis is also common with the bite of the hard-bodied bird tick, particularly in songbirds. Fatal cases of tick paralysis result in finding the tick engorged on the bird's eyelids or head. A secreted neurotoxin is the cause of death in tick paralysis.

Wild birds, particularly babies, are prone to disease from other ectoparasites as well, including mites, lice, fleas and flies. Mites produce mange, while flies can produce maggot infestations on the young birds. Feather loss and anaemia are also common from these parasites.

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