Are animals attracted to light?

Yes, animals are kind of attracted by light (moving behavior).

Animals are attracted to both light and grass. If there is a lot of grass nearby, they will wander toward it regardless of light level. If they are completely surrounded by grass, they will wander aimlessly. If they can't see any grass, they will wander toward light.

Source: http://www.minecraftwiki.net/wiki/Animal

Animals are not attracted to light. If you have not explored a biome yet, there is a one in ten chance that animals will spawn in the new chunks you discovered, and it does not matter if there is light or not. However, for animals to spawn on chunks of the biome that have already been discovered, there must be a light level of 9, and be on blocks with grass http://www.minecraftwiki.net/wiki/Spawn#Animal_spawning. This gives the feeling that animals are attracted to light, though in reality they just happen to be spawning there.