Character displacement from the receiver's perspective: species and mate recognition despite convergent signals in suboscine birds | Proceedings of the Royal Society B: Biological Sciences
TRCA Spring Bird Festival - Toronto and Region Conservation Authority (TRCA)
The Singing Life of Birds | Donald Kroodsma
Full article: Summer in the city: behaviour of large gulls visiting an urban area during the breeding season
Bird Banding | Bill Beatty Nature
birding by ear, with cornell lab of o's all about bird song - A Way To Garden