Microscopic variation in downy feather characters of Charadriiformes (Aves): A descriptive and phylogenetic analysis

It is well-known that the variation in microscopic characters of plumulaceous feathers can be used to aid in species identifications. However, until now, the phylogenetic significance of these characters has not been thoroughly investigated.;In the first part of this study, electron and light microscopy is used to examine the range of variation in downy feather characters of over 145 species of shorebirds (Charadriiformes). Major results of Part I show that similarities and differences exist in the microscopic features within this order; that different downy types (true down vs. whole feather down) of the same individual may have different microscopic structures; that some shorebirds have villi (previously unknown in this group); and thirty-eight microscopic characters are deemed useful for phylogenetic study.;In Part II, parsimony analysis is used to assess the phylogenetic value of these characters by comparing feather results to hypotheses based on osteological data and traditional classification. Three different taxa lists are analyzed using the computer software PAUP;Although initial results of 111 taxa and 38 feather characters found more than 10,000 equally parsimonious trees, it provided evidence that feather characters were tracking some "natural" groupings in this order. Additional analyses on two smaller taxa lists used feather characters alone (38 characters), osteological characters alone (68), and a combination of both character types to search for shortest trees. The final reduced-taxa analysis shows that feather character tree statistics and character indices are compatible to those of osteology. Incongruence in tree topologies is noted in the placement of plovers with sandpipers according to feather characters. Total evidence indices for 154 shortest trees are higher than either of the data sets alone. Convergence in microscopic feather characters of loon and auks has been documented here for the first time and poses a functional hypothesis for nodal morphology.;In this study of Charadriiformes, microscopic feather characters proved to be comparable to osteological characters in tracking phylogeny. However, better results are achieved when the data sets are combined. These results confirm the utility of microscopic feather characters to phylogenetic studies.