Biologia

The Open Ornithology Journal, 2009, 2, 17-23

17

Open Access

The Utility of Plumage Coloration for Taxonomic and Ecological Studies
Eben H. Paxton*
U. S. Geological Survey Southwest Biological Science Center, Box 5614, Flagstaff, AZ 86011, USA
Abstract: Plumage coloration in birds serve multiple purposes, including species recognition, sexual selection cues, and
camouflage.Differences in plumage coloration can be used to infer evolutionary relationships, identify distinct taxonomic
units, and characterize geographic variation. With the advent of electronic devices to quantify plumage coloration quickly
and reliably, taxonomic or geographic differences can be exploited for ecological studies. To evaluate the utility of plumage coloration for taxonomic and ecologicalstudies, I review the basis of plumage coloration and sources of variation. I
then review how different studies have used plumage coloration to better understand taxonomic relationships and provide
insights into ecological problems.

INTRODUCTION
Human interest in the coloration of bird plumage has a
long history, from aesthetic pleasure in the colors, to the
importance of plumage coloration inidentifying species, to
the post-Darwin interest in colorful plumages of many male
birds as they relate to sexual selection. Fascination with
plumage coloration stems from the rich variety of colors and
patterns observed across bird species. Plumage coloration
serves a wide range of functions in birds, including species
recognition, inter- and intra-sexual signaling, and camouflage.However, plumage coloration has received the most
scientific attention for the purpose of grouping taxa, from
early efforts to catalog species, to more recent efforts to
understand evolutionary relationships. Plumage coloration is
believed to help facilitate species recognition, restricting
interspecies gene flow, and thus has high taxonomic value
[1]. Additionally, plumage coloration is believedto be able
to evolve rapidly [2, 3], allowing for fine scale taxonomic
resolution. For this reason, many original species and subspecies descriptions relied heavily on coloration to separate
groups.
However, with the advent of molecular genetic techniques to infer taxonomic relationships, the use of plumage
coloration and other morphological traits for taxonomy has
diminished [4, 5]. Thereasons for the shift are many. First,
the use of genetic markers, particularly neutral markers, is
generally believed to provide a more accurate reflection of
evolutionary relationships, less likely to be biased by directional selection or confused by convergent evolution [6].
Second, molecular genetic markers are quantitative rather
than qualitative, and results can be rigorously tested andin
most cases reliably replicated by other researchers. Third,
the selection of different molecular markers that change at

*Address correspondence to this author at the U. S. Geological Survey
Southwest Biological Science Center, Box 5614, Flagstaff, AZ 86011, USA;
E-mail: Eben.Paxton@nau.edu

1874-4532/09

different rates allows taxonomists to choose molecular
marker most appropriatefor the level of taxonomic resolution they are examining [4].
Additionally, reliance on phenotypic characters, such as
plumage coloration, for the reconstruction of avian phylogenies has been questioned in recent years due to conflicting
taxonomic groupings derived from morphology-based versus
molecular-based approaches [7]. This has been particularly
evident at the intraspecific taxonomiclevel where morphological and genetic differences can be small. For example, in
a study of the geographically widespread Winter Wren
(Troglodytes troglodytes), traditional taxonomic groups
originally identified based on morphological characters did
not always agree with those identified genetically, and in
some cases molecular markers revealed genetically distinct
groups not apparent from...