"Visible light" and near-infrared reflectance of amphibians and reptiles and the visual system of avian predators (Accipitridae:Buteo spp)

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)



First Committee Member

Jay Mathers Savage - Committee Chair


Tropical and subtropical amphibian and reptile species were photographed against natural substrates with Kodachrome and Infrared Ektachrome to record "visible" light (VL) and near infrared (NIR) reflectance relative to natural backgrounds. Species were categorized as either cryptic or aposematic in both VL and NIR or cryptic in VL but conspicuous in NIR. A significant relationship between VL and NIR "color" and suitability as prey was found: innocuous species were cryptic in both VL and NIR, whereas poisonous or venomous species were conspicuous (aposematic). Both cryptic animals and substrate had reflectance maxima at 460 nm, 540 nm and 760 nm/NIR. However, the relative amplitudes of these maxima were disparate. Thermoregulation and predator avoidance are possible explanations for this phenomenon.To determine whether an avian predator is able to visually perceive NIR and detect the prey item/substrate brightness disparities, spectral sensitivity (SS) and wavelength-dependent brightness discrimination of predatory Buteo spp. and non-predatory Columba livia were measured electroretinographically. Scotopic SS of C. livia exhibited a max of 500 nm, whereas the scotopic SS of Buteo spp. peaked at 540 nm.Photopic SS of both taxa peaked at 580 nm. Long wavelength attenuation of sensitivity is present in the pigeon, but not in Buteo spp. A Darnall nomogram curve fitted to SS data for Buteo spp. predicts sensitivity extending to 800 (NIR).Wavelength-dependent brightness discrimination functions of C. livia and B. jamaicensis indicate that the latter can detect brightness disparities similar to those between putatively cryptic arboreal frogs and lizards and their substrates. However, motion and wavelength cues, rather than brightness may be of primary importance in the foraging strategies of diurnal avian predators able to discriminate colors. Near infrared reflectance in tropical amphibians and reptiles may serve as camouflage against NIR sensitive avian predators such as Buteo spp. High intensity green (540 nm) and NIR (760-900 nm) reflectance may have a thermoregulatory function in arboreal species exposed to both full sun (E$\sb{\rm max}$ = 540 nm) and understory illumination (E$\sb{\rm max}$ = NIR).


Biology, General; Biology, Neuroscience; Biology, Ecology; Biology, Zoology

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