Effects of light and prey availability on nocturnal, lunar and seasonal activity of tropical nightjars

摘要: Nightjars and their allies represent the only major group of visually hunting aerial insectivores with a crepuscular andlor nocturnal lifestyle. Our purpose was to examine how both light regime prey abundance in tropics, where periods twilight are extremely short, but nightjar diversity is high, affect activity across different temporal scales. We studied two species West African bush savannah, standard-winged nightjars Macrodipteryx longipennis Shaw long-tailed Caprimulgus climacurus Vieillot. measured biomass potential available using vehicle mounted trap found that it highest at dusk significantly lower dawn during night. Based on direct observations, exhibit most intense foraging behaviour dusk, less least night, as predicted by conditions for visual detection. Nocturnal positively correlated lunar levels ceased below about 0.03 mW m -2 . Over course cycle, availability varied markedly, while remained constant night slightly higher full moon. Both increased new moon periods, compensating shorter window time. Seasonally, pattern similar throughout year, peaked shortly after onset wet season then slowly decreased over following four months. The courtship breeding phenology timed coincide peak insect abundance, suggesting rather than abiotic factors act constraints, seasonal level. findings illustrate peculiar constraints orienting general tropical particular highlight resulting nocturnal, allocation activities.