We bought the Cornell Lab of Ornithology essential set to bird sounds a couple of days ago. It is the introduction deal at $12.99 , saving $7. It has 1376 recordings from 727 different birds. So far I love it. You can buy the Master Set for 49.99 which comes with over 4,000 recordings. So far I love the essential set! Sometimes when I play some of the sounds my mom and dad think they are real birds and are wondering what they are (that happens with my birdsong alarm clock too). I definitely would recommend it if you want to buy bird sounds.
Here's a link to buy it http://macaulaylibrary.org/guide/audio/essential-set-for-north-america