The two species of choughs' ranges. Note that there isn't much overlapping. *Green: Red-billed Chough *Yellow: Alpine Chough *Orange: Both species

Having overlapping ranges [1].


  • 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[2]. 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[2][3].


  1. ^ Bellrose, Frank C. and The Audubon Society (1983). The Audubon Society Master Guide to Birding. National Geographic Society. ISBN 1426200722. 
  2. ^ a b Terres, John K. (1980). The Audubon Society Encyclopedia of North American Birds. Alfred A. Knopf, Inc. ISBN 0394466519. 
  3. ^ Diliger, W.C. (1956). Adaptive modifications and ecological isolating mechanisms in the thrush genera, Cartharus and Hylocichla. Auk (3):313-53
Anatomy of an amiotic egg This article is part of Project Glossary, a All Birds project that aims to write comprehensive articles on each term related to animals.

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