Termination of photorefractoriness in the chukar partridge (alectoris graeca chukar) by low light intensity

Adult females were maintained under controlled conditions (22 degrees C, 60% relative humidity and 16 h light/day) within bioclimatic chambers throughout the test. For 6 weeks prior to photostimulation photorefractory birds were exposed to a light intensity of 1, 3, 5 or 7 lux. The intensity was then increased to 50 lux. Control birds were kept in 8L : 16D and changed to 16L : 8D, the light intensity remaining at 50 lux. The time to first egg and the rate of egg production were recorded. A decrease in light intensity alone was able to terminate photorefractoriness in chukar partridge and the threshold light intensity required for a complete termination of refractoriness was less than 1 lux. Light intensities of 1, 3 or 5 lux resulted in a partial termination of refractoriness but 7 lux was completely ineffective in terminating photorefractoriness. The termination of photorefractoriness was therefore not an all-or-nothing response.