Provably Cardinals are the most frequent visitors to my feeder for these several years. These days they know me well and not afraid so much and I could take these pictures about 20 feet away from them. I think Cardinals have strong bond between pair of male and female through whole seasons. I saw a male Cardinal serve foods to his female partner very often times. Of course I saw other species of singing birds do same things occasionally but they are not so often like Cardinals. So I feel to them very familiarity.