Ian Paulsen, citing this study of subtle differences in plumage that only show up with UV light, asks, "Can a UV Field Guide to North American Birds be far behind? I wonder if a pair of binoculars can be fitted with a lens to see UV light?" UV light doesn't pass through ordinary glass; for lab studies using UV light, we have to use quartz. But only the machines "see" the UV; it won't pass through the lens of your eye, either. I don't know how these studies of plumage with UV light were done--the abstract refers to a video system, and presumably they used a system that absorbs UV light and emits a part of the visible spectrum. So to use this in the field, you'd need a binocular system that takes in UV and produces a specific visible wavelength in response, maybe shifting the whole spectrum by, say, 100 nm or so. Doesn't sound easy. Just how technical and cumbersome do you want your birding experience to be?

Burt Guttman
The Evergreen State College
Olympia, WA 98505 guttmanb at evergreen.edu
Home: 7334 Holmes Island Road S. E., Olympia, 98503

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Robert Bleiweiss (2004) Ultraviolet plumage reflectance distinguishes
sibling bird species . Proc. Natl. Acad. Sci. USA, 10.1073. Published
online before print November 16, 2004

Abstract: Realistic studies of plumage color need to consider that
many birds can see near-UV light, which normal humans cannot
perceive. Although previous investigations have revealed that
UV-based plumage reflectance is an important component of various
intraspecific social signals, the contribution of UV signals to
interspecific divergence and speciation in birds remains largely
unexplored. I describe an avian example of an interspecific
phenomenon in which related sympatric species that appear similar to
humans (sibling species) differ dramatically in the UV. Both UV video
images and physical reflectance spectra indicate that the dorsal
plumage of the tanager Anisognathus notabilis has a strong UV-limited
reflectance band that readily distinguishes this species from its
sibling congener Anisognathus flavinuchus. The main human-visible
distinction between A. notabilis (olive back) and coexisting A.
flavinuchus (black back) also occurs among different geographic
populations of A. flavinuchus. Notably, however, olive- and
black-backed taxa interbreed (differentiated populations of A.
flavinuchus) unless the additional UV distinction is present (A.
notabilis vs. A. flavinuchus). Thus, UV-based reflectance can be an
essential component of plumage divergence that relates to
reproductive isolation, a key attribute of biological species.