Mice have always been huntable species. This fact is explained by many reasons. Due to their fertility and the ability to shake down to any conditions mice live everywhere: at any latitude, in an urban setting, in a country.
Birds are also “loved” by cats. Speaking about the advantages of mice over birds, the first ones are huntable all the year around, while birds migrate to the south from time to time. It’s much easier for cats to catch a mouse, as birds’ eyes are on either sides of the head which make them be all-seeing and prevented. Birds can notice the creeping cat and fly away immediately. Mice can’t boast of such scope, besides they can’t fly.
But the main reason is in chemistry. It appears that the skin of the mouse is rich in microelements, especially in sulfur. Sulfur is the component of cystine and methionine – the elements necessary for cat’s health. So mice are considered to be the essential part of cat’s diet.
Actually, I don’t think so. My cat seems to be quite happy with no mice for meals. I had a rat and they played with each other and there was not a shadow of animosity between them.