2. Comparative Distributions and Structural Adaptations Distributions

• Main Author: Paul A. Johnsgard
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1987
• Subjects: Arctic; Canada; Tundra; Alaska; Tierra del Fuego
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.692.8982; http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article%3D1003%26context%3Dbioscidivingbirds

The geographic distributions of the loons, auks, and grebes are primarily reflections of the evolutionary his-tories of each of the groups, past climatic and geologic phenomena, and present-day climatic and ecological conditions. Thus all the loons and auks are Northern Hemisphere birds, which presumably have never been able to bridge the tropical barrier into the Southern Hemisphere, where seemingly suitable breeding habitat might exist in, for example, southern South America and Tierra del Fuego. Indeed, the breeding distribution of the Northern American loons is distinctly arctic ori-ented (fig. z), with the greatest species density north of the boundaries of arctic tundra in Canada and Alaska and no breeding occurring south of the limits of conti-nental glaciation (see fig. 4).