Summarize this article in one sentence.
Canaries are active birds that enjoy flying around in their cages. If your canary has stopped flying or if they are spending long periods of time on their perch, you may want to take them to a vet. A sick canary may tuck their head under their wings or sleep near their food bowl. A healthy canary should be chirping or singing. A sick canary may be quiet, or they may make wheezing, sneezing, clicking, or coughing noises. Pay attention to their breathing as well. Rapid or labored breathing can be a sign of canary pox or the fungal infection Aspergillosis. Typically, canaries should eat between one and two teaspoons of seed or pellets a day. They should not need their water replaced more than once a day.  If you notice any changes in their appetite, the bird may be ill.  If you find their water dish empty or if they are drinking more than usual, they may be dehydrated. If your bird isn't eating their food, they may have lost their appetite. This is a common symptom of many illnesses. Canaries normally puff up their feathers when they are sleeping or if they are cold. If they are not sleeping, however, and they remain puffed up for long periods of time, it may mean that your canary is unwell. When you change the cage liner every day, check their droppings. Healthy droppings should have clear and watery urine, chalky white urates, and dark, solid feces. Any change in color or consistency means that something may be wrong.  Yellow or green coloration can be a symptom of liver disease. Red or black coloration can be a sign of internal bleeding. Loose or runny feces can indicate that your canary has diarrhea. Healthy droppings should not smell. If you notice a foul odor, it may mean that they have a parasite called giardia. You also might find some discharge and swelling around their nares. Discharge due to sneezing is often a clear sign that your canary has an illness.

Summary:
Note any decrease in activity. Listen to the sounds that they make. Observe how much they eat and drink. Watch for puffed up feathers. Inspect their droppings. Check their cage for discharge due to sneezing.