Going light is the term given to birds that lose weight because they are ill. Most sick birds lose weight simply because they have to burn up their own body tissue to keep warm. So going light is really just a symptom – not a disease.
In finches and canaries, it is mostly caused by a parasite called coccidia. This disease is the subject of this article.
Coccidia are a very common gut parasite. It occurs in many species including poultry and pigeons. It is not common in parrots. Most adult birds can easily tolerate coccidia as their immune system has learned to cope with it. Young birds however are vulnerable because their immune system has not been well developed to cope with it
If these baby birds get infected the bug seems to be able to leave the gut and get into the bloodstream. From there it finds its way to the liver and the spleen. These two organs start to suffer (they will be greatly enlarged at postmortem). While there is enough liver left to cope these birds grow perfectly normally. But when the damage becomes too severe (generally between eight and sixteen weeks of age) the birds start to live in the seed dish but still lose weight until they die.
This is a most depressing illness because a good breeding season can suddenly turn into a disaster.
There are two key ways to tackle this disease. Treating adult birds with appropriate drugs prior to the chicks hatching will reduce the level of infection for the chicks and is a very effective way to prevent the disease.
The more modern approach is attack the germs and stimulate the baby’s immune system with a herbal nutricine.
There is also evidence that a bird can swallow its tongue making it less likely to feed and consequently lose weight. Check that the tongue is seated correctly and if there is evidence of it being swallowed, the use of a fine implement (cocktail stick) carefully inserted under the tongue and pries forward will reseat the tongue into the natural position. Then keep bird under surveillance to ensure it is eating and on the road to recovery.