Mirrors have a complicated reputation in the bird community, but they probably won’t do any harm to your finch. A finch may even find a mirror fun to play with. However, there are a few potential risks to be aware of.
The problem with mirrors is that they have been thought to cause aggression in some bird species. A bird sees what it thinks is another bird in the mirror, and becomes attached. They can then start acting distant and rude to the owner, especially if they get in the way of the mirror.
Birds who have become overly attached to a mirror can start to act out. They can’t receive any affection from the bird in the mirror, causing them to feel upset and confused.
However, this isn’t always the case, and some birds do perfectly fine with mirrors. Signs of aggression are more common in bigger birds, and there are some who believe that a small bird like a finch needs a mirror. The mirror can keep the finch entertained when the owner isn’t around, and acts sort of like company.
If you choose to get a mirror toy for your finch, it’s best to do so once you’ve already bonded. That way, the finch is less likely to replace the owner with the mirror.
Introduce the mirror to the cage, and see how the finch reacts. If it seems to be responding negatively, then simply remove the mirror. The mirror should only be small, and the finch must have other forms of entertainment. A finch doesn’t necessarily enjoy playing with a mirror over different toys.