Whereabouts do you live? Not all sparrows, but house sparrows in particular are considered an invasive species in North America and are known to be very aggressive toward other bird species, kicking them out of their nests, and such. We have a ton of them in our backyard and they are virtually impossible to get rid of to make room for others, like bluebirds.

On a more positive note: we do get cardinals every so often. Just saw a male and female on our feeder this morning.