Brilliant orange bills are a striking contrast to the sooty gray plumage of the crested auklet (Aethia cristatella), a colonial seabird of Alaska and Siberia. We characterized this pigment with three spectroscopy techniques. With Raman Resonance Spectroscopy we identified a fluorescence peak at ~527 nm (similar to YFP-10C). Using fluorescence spectroscopy (FS) we found the fluorochrome is unique in the Genus Aethia, but we also found phenotypic differences. Our samples from St. Lawrence I., AK were all single-band fluorescence (n=11), while Little Diomede I. (LD) included single and two-band phenotypes (n=10). Crest size, a signal of dominance, correlated with highest fluorescence in the single-band phenotype (r_{s 1-tailed} = 0.48, p=0.04, n=14). The fluorochrome has absorbance spectra similar to known pterin compounds (6-biopterin, pterine, pterin-6-carboxylic acid). Interestingly, euphausiids, a favored food of crested auklets, overlapped in their absorbance spectra with the fluorochrome. We assayed for an effect on behavior of using decoys that differed only in bill fluorescence. Crested auklets approached the models with fluorescent bills at a higher frequency (t₍₃₄₎ = 2.78, p_1-tailed = 0.004). We suggest that a preference for the fluorochrome could have evolved by exploiting a preexisting bias in crested auklet visual systems, linked to a prey preference. The possibility that bill color may advertise foraging ability was supported when in the marine heat wave of 2016, 11% of crested auklets captured at LD had incomplete bill pigmentation.