SHORT COMMUNICATIONS 
377 
mental conditions, did not use ultraviolet markers 
to detect the presence of prey, as do diurnal 
raptors (Koivula et al. 1997). These factors in 
composite suggest ultraviolet fluorescence may 
not be a social cue. although further investigation 
is needed. 
ACKNOWLEDGMENTS 
The authors are grateful to D. H. Johnson. C. E. Braun, 
and an anonymous reviewer for their comments on an 
earlier draft of this manuscript. We thank Jamie Acker, 
Dawn Garcia, and Stan Rullman for sharing observations 
and photographs of fluorescence in Pacific Northwest owls 
and Jeff Smith for observations on Flammulated Owls. 
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