Having overlapping ranges .
- William C. Dilger studied five species of N. American thrushes - Wood Thrush, Veery, Hermit Thrush, Swainson's Thrush and Grey-cheeked Thrush - in which males cannot be distinguished outwardly from the females, and discovered that the males and females recognised each other by their behaviour. He also concluded that the songs and calls of the male thrushes, that are different in each species, were the primary signs by which females recognised males of their own kind.
- ^ Bellrose, Frank C. and The Audubon Society (1983). The Audubon Society Master Guide to Birding. National Geographic Society. ISBN 1426200722.
- ^ a b Terres, John K. (1980). The Audubon Society Encyclopedia of North American Birds. Alfred A. Knopf, Inc. ISBN 0394466519.
- ^ Diliger, W.C. (1956). Adaptive modifications and ecological isolating mechanisms in the thrush genera, Cartharus and Hylocichla. Auk (3):313-53
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