Phototactic responses of anuran amphibians to monochromatic stimuli of equal quantum intensity.

The phototactic responses of anuran amphibians to narrow-band monochromatic stimuli of equal quantum intensity were measured for the first time in eight new experiments. The unimodal spectral response, obtained from dark-adapted American toads (Bufo americanus), peaks near 626 THz of frequency (480 nm wavelength). The bimodal, U-shaped spectral response, obtained from dark-adapted tailed frogs (Ascaphus truei), has the anti-mode at about 589 THz (510 nm) and is not merely the spectral mirror-image of the unimodal response. Absolute level of the spectral stimuli of equal quantum intensity did not affect the spectral response of dark-adapted toads, but light-adaptation enhanced a component that has the same spectral peak as the visual pigment absorption spectrum of principal and single cones of the frog's retina.

Differential aggression in genetically different morphs of the white-throated sparros (Zonotrichia albicollis).

To see if genetic differences correlate with differences in agonistic behavior, 225 encounters within and between color morphs of the white-throated sparrow (Zonotrichia albicollis) were observed in feeding groups of different sizes and morphic compositions. Tan morphs lack the M chromosome that replaces either of two chromosomes in the white morph. The data were analysed using quantitative models accounting for the proportions of morphs present, and the principal finding was that morphs are equally frequent recipients of aggression but the white morph was the aggressor more frequently than by chance expectation--regardless of the morph of the recipient, the size of the group or the morphic composition of the group.

Ontogenetic shift of spectral phototactic preferences in anuran tadpoles.

Tadpoles of three species of anurans initially had a midspectrum ("green") preference in laboratory phototactic tests, which was shown experimentally to involve a form of true color vision in one species and probably in the other two as well. During development, the preference shifted to shorter wave-lengths (higher frequencies) until a short-wavelength ("blue") preference predominated in the pre- and postmetamorphic stages and in the adults of six species tested; color vision was involved in all of these stages. The green preference of young tadpoles is ecologically adaptive, in that it directs larvae to green plants that provide food or shelter. Tadpoles observed in a pond congregated heavily in vegetated areas rather than in open water. Spectroradiometric field measurements showed that pond illumination in vegetated areas had a more highly saturated yellow-green spectral dominance compared with a desaturated white illumination in open water. During all ontogenetic stages and as adults, the animals had a preference for high illuminance of white light, which correlates with the high illumination of their habitat. Microspectrophotometric data from Liebman and Entine suggested that the green rods are active receptors in tadpoles, making unlikely Muntz's hypothesis that the ontogenetic shift in spectral preferences is due to premetamorphic maturation of these receptors. However, the visual pigments of all five types of photoreceptors shifted from vitamin A2- to vitamin A1-based chromophores during ontogeny, and the resulting shift in spectral response of the receptors might be related to the spectral shift in phototactic preferences.

Oildroplets in the eyes of adult anuran amphibians: a comparative survey.

Oildroplets in the eyes of terrestrial vertebrates are spherical cellular organelles that stain for lipids, have no discernible internal structure, and often contain carotenoids and possibly other chemicals. A survey of 97 species of anuran amphibians (frogs and toads) revealed that all species of 16 families surveyed possessed yellow oildroplets of varying size in the cells of the pigment epithelium, except for three species that appear to have secondarily lost them during evolution. Furthermore, 25 species of six families also possess colorless oildroplets at the distal end of the inner segments of single cones and principal cones of the double-cone system; two species of the Ranidae appear to have secondarily lost such retinal oildroplets. Every species possesses epithelial or retinal oildroplets or both. Lastly, small oildroplet-like inclusions were discovered in the red blood cells of two species. All of Walls' ('42) summary generalizations about anuran oildroplets are incorrect: oildroplets are not restricted to the Ranidae, are not yellow when found in the cones, and do not correlate with photoactic behavior in 87 species. Evidence is reviewed suggesting that the primary function of anuran oildroplets is chemical storage, perhaps related to the visual pigment cycle. Oildroplets in the cones may additionally act as filters of ultraviolet radiation.

Similarity of approach and pecking preferences for spectral stimuli in domestic chicks: absence of a mirror-image relation.

The results of Schaefer and Hess showing that White Rock chicks described mirror-image response functions to spectral stimuli in approach and pecking behavior could not be replicated using Cornish-Cross chicks under more controlled conditions. Our results showed similar blue-orange bimodal functions for both behavioral responses, resembling the approach data of Schaefer and Hess and the earlier pecking data of Hess and others, but not the pecking data reported by Schaefer and Hess.

Temporal pattern shifts to avoid acoustic interference in singing birds.

Two species of forest birds, the least flycatcher and the red-eyed vireo, when breeding in the same season in the same habitat, adjust their temporal pattern of singing to avoid the overlapping of songs. The avoidance of acoustic interference is more marked in the flycatcher, which has a briefer song than the vireo.

Spectral reflectance of gull's bill: physiological and evolutionary implications for animal communication.

The newly hatched laughing gull chick (Larus atricilla) begs food by pecking at the parent's dark red bill. The spectral reflectance of the bill over a range of 300 to 1200 nanometers reflects increasingly more with wavelength beginning about 575 nanometers. Because the chick shows a bimodal, true color preference in pecking, with modes at about 625 and 450 nanometers; the latter, blue peak in the spectral response curve is apparently not adapted to the natural stimulus of the parent's bill. The blue peak might thus be the result of limitations in the neural coding of color information in the chick's visual system.