Why does my canary sit on the aviary floor?

I set up my aviary about a month ago. I have six canaries, four Java Sparrows, eight zebra finches and three Chinese painted quail. All seemed fine, but this week one of the canaries has just sat on the floor all puffed up and only flew up to roost at night. I then noticed that one of the male zebras is holding one foot up, and doesn't seem to be able to bend his toes. What could be the cause of this?
R.H., via Facebook.

Brian Keenan, current president of the Yorkshire Canary Club, replies: You do not mention the size of the aviary, or the number of feeding stations, but placing so many birds in to an aviary at the same time may have contributed to the problem. Birds are territorial and will fight to establish a "pecking order" in a mixed group. Toes can easily be nibbled or damaged if the birds are scared and fly haphazardly into the aviary wires. The canary could simply be moulting, or perhaps suffering from mite.

Segregating the birds with problems is a wise precaution, allowing you to treat them as necessary. For example, applying witch hazel or a similar product to the damaged foot of the zebra finch, or holding the canary to check for mite, weight loss or other symptoms, and then treating accordingly.

Observe your aviary inmates closely and watch for any aggressive behaviour. This will be readily demonstrated at feeding times, so always provide multiple feeding stations. Remove any bullies at the first signs of trouble.