Predatory birds are often at risk of infection from parasites carried by birds of prey. Any disruption of the birds feathers or body temperature causes lice, flies, and other parasites to move quickly to the surface of the feathers and prepare to transfer to a new host.
Bird banders often see hippobscid flies leave the host bird as it handled in the process of banding and often encounter mallophagan lice and feather mites as well. These parasites are bird-specific and no threat to humans, but with the recent rise of Lyme disease, banders and others who routinely handle wild birds should be aware of the relatively minor risk of infection from deer tick larvae.
Parasitic flies (Order Diptera) are the most common bird ectoparasites. The finch louse fly (Hippoboscidae Ornithomyia frongillina) infests more than 100 species of birds around the world. These flies have an extremely flattened body so they can better fit into gaps between the feathers where they lie flat against the birds skin. They also have strong sharp claws that cling to feathers and skin. Their sucking mouthparts cling to and extract blood from the bird. They can act as vectors for disease and sometimes kill young birds because of blood loss.
These hippoboscid flies have an unusual and complex life cycle. Female flies retain a single developing larva within their bodies and give birth to live, fully formed flies one at a time. They require no alternative or intermediate host in their life cycle; and, under favourable conditions, several generations of flies may live out their lives on a single bird. Phoresy is a parasitic phenomenon while hippoboscid flies transport another parasite, known as the mallophagan louse. These lice attach themselves to the abdomens of hippoboscid flies and go where they go.
Bird lice suck blood from both mammals and birds. The Suborder Mallophaga are sucking lice that feed on a birds feathers as well as sucking blood through the birds skin. These lice can live under and between feather shafts; but one species is so specialized that it lives on blood, other fluids, and pith within the shaft of the developing feather calamus. Those who handle birds often find the lice in larger birds like hawks and eagles. While the birds seem to be only slightly annoyed with their presence, heavy infestations can seriously damage the plumage, causing the bird to be exposed to weather and degrading the performance of its flight feathers.
Mallophagans attach their eggs directly to the feathers or lay them within the feather shafts. Most species are so closely adapted to the host bird that the lice have been used to determine taxonomic relations within closely related groups of birds. As bird families evolve, the lice associated with them follow a parallel development. For example, ornithologists have long suspected that the large ground-dwelling ostrich (Family Struthionidae) and rheas (Family Rheidae) share a distant common ancestor. Interestingly, the mallophagan lice on both groups also show evolutionary affinities, suggesting an ancient relationship between the parasite and its host.
Mites are another parasite that attack birds. There are several groups of such parasitic mites (Order Acarina).
- Feather mites (Family Analgesidae) do not suck blood but rather feed on the feathers and debris that normally flakes off from the skin and plumage. Usually, they do not bother the bird too much; but heavy infestations can cause feather mange, a condition that can cause large patches of feathers to drop off the body.
- Itch mites (Family Sarcoptidae) often infest the legs and feet of birds. They live under the scutes and scales of the skin. Serious infestations can cause swelling and debilitating infections of the legs.
- Nasal mites (Family Rhinonyssidae) infest the nasal cavities of birds, particularly birds that feed on nectar and visit many flowers each day. The mites use the birds for transport from flower to flower. Once at a new flower, the mites infect the next bird that feeds there. Heavy infestations can restrict air flow and cause respiratory infections.
- Red mites (Family Dermannyssidae) infest the nests and roosts of birds, attacking resting adults and nestlings during the night. Large populations of red mites can kill nestlings and become permanent residents on the bodies of adult birds.
Bird fleas (Order Siphonaptera) are blood-sucking parasites that attack birds. This group tends to infest nestlings and birds that habitually use the same roosting area. Because fleas spend their early lives feeding on organic debris in and around nests, they have several disadvantages relative to parasites that live permanently on their hosts. The eggs and larvae are restricted to activity during the warmer months. Eggs are laid in nest debris from the host bird or in ground litter. Therefore, each new generation must find a new host bird as they mature or they will die out. Fleas that attack birds derive primarily from two families, the rodent fleas (Family Dolichopsyllidae) and the sticktight fleas (Family Tungidae). Fleas act as vectors for disease and can be so numerous around infected nests that they can kill young nestlings.
Bird ticks (Family Ixodidae) attack the fleshy parts of the bird and are often found around the gape of the mouth, ears, and eyelids. In extreme cases, ticks can cause eye diseases and blindness. Ground-living birds and birds that roost communally are more susceptible to tick infestation than more arboreal, mobile species. Most ticks have a complex life cycle and spend some of their lives living in debris around the hosts nest or roost.
Young tick larvae often attach to a bird, obtain a blood meal, and then drop off again to complete the metamorphosis to adulthood. The adult tick then seeks a new host bird and may stay permanently attached if it finds a suitable host.
Many factors limit populations and thus keep their numbers, in and around nests, from becoming overwhelming. These blood-sucking parasites have become famous in recent years as the vector for Lyme disease. Research has shown that birds may harbor the larval stages of the deer tick (Ixodes dammini) that actually transmits the Lyme disease spirochetes. In a study conducted in eastern Connecticut, twenty-seven bird species from eleven families were found to be carriers of I. dammini larvae.
Proctor, Noble S., and Patrick. J. Lynch. Manual of Ornithology: Avian Structure and Function. New Haven, CT: Yale University, 1993.
This page was updated in June 2006.