Suspect Cases of Scaly-Leg in Pine Grosbeaks

Male pine grosbeak. Photo Credit: DM Jefferson

Recently, pine grosbeaks (Pinicola enucleator) exhibiting a clinical presentation consistent with that of scaly-leg disease have been captured at banding stations in Saskatchewan and Alberta.

No previous instances of pine grosbeaks diagnosed with scaly-leg appear to exist in the literature, so the cause of this presentation remains unclear. However, a similar presentation has been diagnosed in many other species of wild passerines (e.g. evening grosbeak, robins, red-winged blackbirds, grackles, cowbirds, house wrens, house sparrows, etc.) in which it has been associated with an infestation of parasitic mites. These mites burrow into the epithelium (the top layer of skin) of un-feathered areas of the bird’s body (e.g. around the beak, eyelids, legs, feet, and/or vent) where they feed on keratin. As they feed, the mites create tunnels through the epithelium, damaging the tissues as they proceed. This causes irritation to the infected bird and the infected area becomes swollen and develops a discoloured and crusty or scaly appearance.

When this disease occurs in the legs of birds, the infection is commonly referred to as scaly-leg due to the swollen crusty/scaly appearance of the affected appendages. Infections appear most common in older birds. Chronic infection can lead to lameness, deformation of legs and/or feet, potential loss of parts of the legs or feet, and can potentially result in death. In wild birds common clinical presentation include discoloured and swollen crusty/scaly legs and/or feet, lameness, and/or an inability to perch.

Pine grosbeak exhibiting clinical presentation consistent with that of scaly-leg disease caught at a bird banding station in Prince Albert, SK. Photo Credit: DM Jefferson

The mites typically spend their entire lives on the infected bird, though transmission of mites typically occurs through prolonged close or direct contact among birds. However, the potential also exists for transmission through contact with contaminated objects (e.g. bird feeders).

Help prevent the spread of transmissible diseases through your bird feeders, be sure to monitor birds at your feeder for signs of illness and remember to thoroughly clean your bird feeders/baths with warm soapy water and disinfect them using a 10% bleach solution (1 part bleach in 9 parts warm water) twice a month. Please report any incidents of dead or sick birds you encounter to your nearest Canadian Wildlife Health Cooperative regional centre.