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THE WILSON JOURNAL OF ORNITHOLOGY . Vol 123, No. 2. June 2011 
DISCUSSION 
This technique was developed for Bam Owls, 
and is described here primarily for Northern Saw- 
whet Owls. However, it appears to have wide 
applicability to many, if not all, species of owls. 
We and others have tested black UV lights on a 
variety of wild and captive North American owls, 
and all fluoresce. Eastern Screech-Owls (Mega- 
scops asio) exhibit a pattern and color almost 
identical to Northern Saw-whet Owls, as do 
Flammulated Owls ( Otus flammeotus) (Jeff Smith, 
pers. comm.), while two captive adult Barred 
Owls (Strix vciria) examined under black UV light 
showed a bright, violet-magenta fluorescence on 
newly molted remiges, but a complete absence on 
rectrices. Wild Barred Owls (classified as SY and 
ATY) examined in Washington Stale showed 
clear molt limits in the remiges with three 
generations easily visible in the ATYs (Jamie 
Acker, Dawn Garcia, and Stan Rullman; pers. 
comm.) A captive adult Great Homed Owl had 
weak fluorescence when initially examined, but a 
year later exhibited bright magenta fluorescence 
on newly molted remiges, perhaps a result of a 
stronger UV source. An unknown-age Northern 
Pygmy-Owl (Glaucidium glioma) examined in 
August in Washington State exhibited bright 
fluorescence on the underwing coverts and faint 
fluorescence on the base of the remiges (Jamie 
Acker. Dawn Garcia, and Stan Rullman; pers 
comm.). 
An HY Long-eared Owl (Asio otus), found 
freshly killed by a larger raptor in early Decem¬ 
ber, had an even distribution of pale lavender 
fluorescence only at the base of the flight feathers 
where they had been covered by coverts, but 
exhibited strong fluorescence on the down 
feathers of the tarsi and flanks. An HY Long¬ 
eared Owl captured in November had a similar 
pattern, while an AHY Long-eared Owl netted at 
the same time had distinct flight feather molt 
limits under black UV light with new feathers 
fluorescing brightly. The molt limits were diffi¬ 
cult to detect on the same bird using incandescent 
light. The fluorescence was purple-red shading to 
dark purple, and no fluorescence was noted on the 
rectrices, contour feathers or dorsal surfaces. 
One concern is the effect of exposure to UV 
light on the eyes of both owls and banders. 
Ultraviolet wavelengths can cause tissue damage, 
although the long wave (UVA, 400-315 nm) 
radiation produced by commercial black UV 
lights is considered the least damaging of the 
three wavelength categories of ultraviolet light, 
and is found in most light sources, regardless of 
type. However, UVA bulbs may emit trace 
amounts of more damaging UVB radiation (Stell- 
man 1998). There appears to be little information 
suggesting that brief exposure to UVA light 
experienced during normal banding operations 
would be harmful to owls, but caution is 
warranted. We make an effort to shield the eyes 
of owls during UV examination, often by shading 
the bird with a hand, and keep exposure as brief as 
possible. 
A growing number of bird taxa have been 
shown to see wavelengths of light in the UV range 
(Bennett and Cuthill 1994, Bowmaker et al. 1997. 
Wilkie et ;>1. 1998. Cuthill et al. 2000). and UV 
reflectivity has proven important for some birds in 
mate selection (Hunt et al. 2001. PeameiaJ. 2001. 
Arnold et al. 2002, Hausmann et al. 2003) and 
hunting (Viitala et al. 1995, Koivula and Viitala 
1999). 
Recent research suggests that many taxa that 
appear monomorphic in visible light may be 
highly dimorphic when viewed in the UV range 
(Andersson et al. 1998). A recent plumage survey 
of ~ 1,000 nonpasserine bird species showed 
distinctive ultraviolet reflectivity, suggesting this 
visual ability may be widespread (Mullen and 
Pohland 2007). 
Fluorescence differs from reflectivity, but the 
presence of abundant pigment in owl plumage that 
fluoresces brightly prompts the question: can the 
owls see this color and. if so. might it have a 
social or behavioral role, such as in mate 
selection? The absence of visible fluorescence 
on dorsal surfaces, head or face of owls examined 
under black UV light argues against its use :ts a 
social signal, although the underwing surfaces 
where it is present would be observable in flight, 
such its during courtship rituals, and surfaces that 
reflect UV light may not fluoresce. The amount of 
UV light reflected by the moon is exceedingly low 
(the moon's albedo is just 0.038; Henry et al 
1995), and may be below the threshold for visual 
detection, although many owls are active at dusk 
and dawn, when UV intensity may be greater 
However, examination of the eyes of the Tawny 
Owl (Strix alued) suggests owls lack the ultravi* 
olet-sensitive/violet-sensitive (UVS/VS) cone 
class associated with ultraviolet vision (Bow- 
maker and Martin 1978, Cuthill et al. 2000). 
Boreal Owls (Aegolius funereus), under experi- 
