Your finch pair is fighting and you'd like to know the reasons. I will attempt to explain some of the more complicated issues of finch pair aggression in this article. This article is written on the basis that you have a pair of finches in a cage or aviary. If you have a colony set-up other factors for aggression will come into play.

New pairs:
For new birds simply being in a new home is reason enough to show aggression. The stress of being moved from one home to another could lead a new bird to attack first and socialize later. Suddenly being tossed into a cage with an unfamiliar finch is quite stressful. Add to that the stress of being caught, transported, moved to an unfamiliar environment and sometimes suddenly switched to a new diet. Everything happening all at once is a lot with which a small finch has to deal.

New finches should always be given time to adjust to their new home. It's up to you to make the adjustment time as easy as possible. No loud noises, abrupt changes to the cage, don't switch to a whole new diet plan right away, and more importantly no nest.

Basic tips for giving your finch a happy home:
  1) Don't over-crowd the cage with finches or items
  2) Provide and balanced and varied diet
  3) Supply adequate light and temperature
  4) Give them a little privacy
  5) Remember, finches will breed when they want to, not always on your schedule

Reasons for sudden onset of aggression with established pairs

They have been given a nest but you always remove the eggs:
This is something you can do and it is a method for preventing reproduction but it isn't the best method.

From the finches perspective a lot of time and energy has been invested in a mate and apparently the mate is incapable of producing young. It doesn't matter that you are the reason for the pairs infertility they simply see fault with their mate. This can trigger sudden and sometimes very violent aggression in either sex. The finches want to breed and if their current mate can not produce young then a new mate must be found. Doing this in a cage setup with only the one mate available presents a problem hence fighting ensues.

There are two ways to fix this problem. You can either remove the nest, which will hopefully remove the trigger for the aggression. Or you can let the pair raise a clutch of chicks. Separating the pair for a time may also be necessary. If one has been plucked it will continue to be plucked until you give it time alone to regrow feathers.

You'll notice I didn't include the third possible option. The third is to find new mates for the finches. If you do find new mates and continue to remove eggs from the nest you'll end up right back where you started after awhile.

They want to breed but don't have a nest:
You should be able to see this one coming. If your pair has torn up everything they can get their beaks on to make a pseudo-nest; they really want to breed. In finches the drive to breed is very strong and you can't always avoid it.

The pair will use anything you give them to build a nest, even if the nest is merely a pile of paper bits in the corner of the cage. However what starts with scrap material laying around the cage soon turns into fluffy feathers. The plucking tends to start slow but quickly snowballs into a partly bald finch or two. After that they usually become aggressive towards their mate.

The first thing to do is to separate them. If it has gotten to the plucking stage they will each need time alone to regrow their feathers. Once they are back in full feather you can put them back together again, and for a time they may get along. It doesn't usually take more than a few months for the behaviors to resume.

Once again you have two options. You can give them a nest and let them raise a clutch. One clutch of chicks a year is often all it takes to keep a pair content. Or you can separate the pair indefinitely.

Finding new mates is another option but as before if you do repair them but don't allow breeding, you'll probably end up back where you started.

One wants to breed but the other doesn't:
This is common, especially with younger birds. Most males come into breeding condition and breeding readiness long before females. Some male Zebra finches can breed as young as 4 months old. It's rare but it can happen. Female Zebras on the other hand don't usually start producing eggs until they are 6-9 months old.

The trend is typical with all finch species but the ages vary from species to species. It is because of this that most breeders don't sell young finches or tell buyers not to give them a nest for a number of months.

The nest only helps to trigger the breeding cycle in finches. If the male is physically ready but the female isn't they will probably fight. Always check with the breeder when buying any finch. You'll want to know how old the finch is and at what age the finch will be ready to breed. When buying from a pet store, assume the finches won't be ready to breed for the next 3 months and you'll probably be ok.

Old age or illness:
It's sad but true. Some finches do not like elderly or sickly mates. These mates rarely produce offspring anyways. This reason for aggression doesn't happen very often but that doesn't mean it will never happen.

The only way to handle this problem is to separate the pair. If the mate is simply ill and you can treat it, then you may yet be able to put this pair back together.