Figure 1.
A comparison of carotenoid and visual pigment absorbance spectra, food and background reflectance, and irradiance spectra of the experimental lighting.
(A) Absorbance spectra of single-cone photoreceptors before (gray lines) and after (black lines) carotenoid-pigmented cone oil-droplet filtering. Spectral sensitivities are based upon measures from the canary (Serinus canaria; [28]), the house finch's closest relative for which these values are known. Microspectorphotometric studies [10] suggest that the long-wavelength-sensitive cone (LWS) is filtered by an oil droplet pigmented with astaxanthin, the medium-wavelength-sensitive cone (MWS) is filtered by a zeaxanthin-pigmented oil droplet, the short-wavelength-sensitive cone (SWS) is filtered by a galloxanthin-containing oil droplet, and the ultraviolet-sensitive cone (UVS) has a transparent oil droplet. (B) Normalized absorbance spectra of carotenoids found in the house finch retina: astaxanthin (asta), galloxanthin (gal), zeaxanthin (zea), lutein (lut), and ε-carotene (ε-car). (C) Sample irradiance spectra from the full and red-filtered room lights and reflectance spectra of the food pellets and distracters. Irradiance spectra are presented in gray and are associated with the y-axis on the left. Reflectance spectra are presented in black and associated with the y-axis on the right.
Table 1.
Total irradiance and predicted visual contrasts between food pellets and background distracters under experimental illumination modeled assuming either bright or dim (photon-noise limited) conditions.
Figure 2.
Retinal carotenoid levels in experiment two.
Mean ± S.E. concentration of the six carotenoid types in retinas of female finches receiving a low-carotenoid (open bars) or zeaxanthin-supplemented (solid bars) diet in experiment two. *indicate significant treatment differences.
Figure 3.
Foraging performance under experimental lighting conditions.
Mean ± S.E. number of food pellets eaten by male and female house finches in experiment one, and by female house finches in experiment two under high-contrast full-light vs. low-contrast red-light conditions.
Figure 4.
Carotenoid supplementation and foraging performance.
Mean ± S.E. change in the number of food pellets eaten by finches in the red-filtered light (solid bars) and the full light (open bars) following eight weeks on a low carotenoid, astaxanthin- (asta) supplemented, or zeaxanthin- (zea) supplemented diet.
Figure 5.
Food color preferences of carotenoid-supplemented birds.
Mean ± S.E. number of seeds dyed each of four colors eaten during the 20 min food preference trial. Diet treatments are denoted with different symbols.
Figure 6.
Retinal carotenoid levels and low contrast foraging performance.
Relative number of food pellets eaten in the low-contrast red-light, as compared to high-contrast full-light, in the post-supplementation period for (A) experiment one, (B) experiment two, and (C) experiments one and two combined. The diet treatments within experiments one and two are denoted with different symbols. The box plot in at the top of figure C represents the natural range of variation in retinal carotenoid levels among wild house finches reported by Toomey and McGraw [18].