Patterns of morphological evolution in bird genera of New World and Old World peatlands.

Habitats selected by bird species in peatland shrub and forest areas of Minnesota were similar to those in Finland. Open peatlands in Finland, however, had more water pools and less vegetation than those in Minnesota. Morphological analysis used 15 characters: size and 14 shape variables (skeletal measurements adjusted for size) pertaining to 3 functional complexes (bill, flight apparatus, and hind limb). Emphasis was placed on 4 genera in Minnesota, Zonotrichia, Spizella, Geothlypis, Dendroica, and one genus in Finland, Emberiza. In all 5 genera, species in shrub vegetation are consistently smaller, have relatively longer pelves and legs, and have wider and shallower sterna than their respective congeners in coniferous forests. With the exception of Emberiza and Spizella, the bill, sternum, and humerus are relatively longer in the shrub-dwelling peatland species than in their respective congeners in coniferous forests. The most abundant species in the shrub vegetation in Minnesota (Cistothorus platensis) and in Finland (Acrocephalus schoenobaenus) are among the most extreme in this respect; they are relatively small, with relatively wide and shallow sterna, relatively long bills, and relatively long pelves and legs. Also, warblers breeding in shrub peatlands have relatively deeper and wider bills, but sparrows have relatively shallower and narrower bills than their respective congeners in coniferous forests. These morphological relationships indicated significant directional patterns of differentiation among distantly related genera (warblers and sparrows) for morphology associated with movement through the habitat. Morphological differences associated with feeding, however, showed trends at the family level that probably reflect differences in diet and behavior between sparrows and warblers.-from Author