My cat eats birdseed. Here is the proof in a video! Although, it is important to note that he only nibbles a small amount. This is what I’d expect. It would be highly peculiar if a domestic cat ate lots of birdseed. It would be a health issue both in causing it and the effect that it might have on their health. But domestic cats are inquisitive and they tend to nibble stuff that is on the ground. That’s my experience. They might eat a bit of it and then spit the rest out. I think it’s all part of a cat’s natural inquisitiveness and search for food. Perhaps in nibbling birdseed they are testing it out to see whether it is edible.
It is, however, highly ironic because a good percentage of birdseed, as I understand it, is grain and there is a lot of argument on the Internet about commercially prepared cat food containing grains and this sort of cat food is deemed to be of poor quality. Here I have my cat enjoying eating grains. Also, it is the food of a bird and domestic cats prey on birds much to the chagrin of ornithologists. And finally, it is my cat temporarily becoming a vegetarian. It’s is turning the world on its head for a brief period of time.
Below are some pages on strange cat behavior.