Recently, I received an email from someone in distress over an obviously sick crow in their yard. They sent some photos and were wondering about the cause of the crusty areas around the bill and eyes. Although I am by no means an expert in avian diseases, there’s one that’s easy to identify and by far the most common I see in the field so I feel it’s appropriate to provide a brief description of it here.
Avian pox is a common disease affecting birds across many different orders including songbirds, raptors and game birds. It’s caused by the avipoxvirus of which there are at least 3 different strains. There’s multiple modes of transmission but it’s most often spread by mosquitoes which is why it’s observed more commonly in the spring and summer months. It can also be spread via direct transmission or indirectly through inhalation of dander, feather debris or sharing contaminated food or water sources (a good reminder to regularly clean feeders and bird baths).
There are two types of avian pox: wet and dry. Wet pox affects the mouth, throat, trachea and lungs and is most likely to be fatal because it can eventually cause suffocation. Dry pox infections are easy to identify because they result in visible lesions and scarring on the non feathered areas of the bird. In the early stages small yellow, white or pink blisters form which become large raised areas that eventually burst. This results in the formation of crusty scabs that, on crows, will appear brown or black. As long as the the bird’s ability to feed isn’t influenced by the location of the scabbing the lesions will generally heal in 2-4 weeks. The general health of the bird before the infection, and the presence of any secondary infections that result from the open lesions will influence the bird’s likelihood of survival.
If you notice pox infected birds at your feeder(s) the best way to protect your visitors is to stop feeding them. This may seem cruel or counterproductive since sick birds need access to consist food sources to fight the infection, but providing food bonanzas concentrate birds and increases the risk of transmission to healthy individuals. Depending on your situation you may be able to provide food to the individual without worry of creating contact between multiple birds.
Please leave a message in the comments if you have high quality photos of your infected birds and would be willing to let me use them in this post. Thank you!