Color pecking preferences in White Leghorn chicks.

Studies of color pecking preferences in newly hatched chicks (Gallus domesticus) have shown unimodal preference in the orange region of the spectrum or bimodal preferences at blue and orange. In the present study, dark-harched White Leghorn chicks were tested in darkness with targets illuminated at 1 or 3 radiant intensity levels. Results showed the least amount of pecking at green (541 nm.) and peak preferences in blue-violet and orange-red regions. Findings were similar when other dark-hatched chicks were tested in the light (Experiment 2). Overall, findings suggest unlearned pecking preferences for short and long wavelengths, with minimums at green. Possible evolutionary and photochemical bases for such a bimodal wavelength preference function were discussed. Since bimodality was unaffected by target intensity and background, these variables probably do not account for the unimodal function reported by others.