On May 2nd of this year I was suprised, and delighted to see two male Indigo Buntings foraging under my feeders next to 3 or 4 White-crowned Sparrows and a few White-throats. Indigo Buntings are breeders here in CT, but White-crowns breed far to the north in Canada.
To me, one reason to love the bird migrations (especially Spring when they are in their breeding best) is the chance to see species intermingling with others species that breed in entirely different habitats and parts of the country. I like to compare it to a music festival.... everyone comes from all over for one, beneficial reason. Hippies have the music and peace, and birds have uncrowded breeding grounds and fresh crops of food.