Habitat Selection, Ambient Light and Colour Patterns in Some Lek-Displaying Birds

Abstract

Ambient light is probably the most variable physical factor in tropical rain forests. High light intensity above forest canopy is reduced through tall and dense vegetation to about 0.1 – 1 % in the understorey. Moreover, whitish ambient light spectra of direct sunlight is drastically changed to yellow-green in forest shade, to bluish in woodland shade, or to yellow-orange in small gaps depending upon the geometry of vegetation and the fraction of the sky covered by cloud (Endler 1993). In addition, in these habitats ambient light is purple at dawn and dusk, and converges to white with cloudy weather during the day. These changes in light quantity and quality have profound effects on seed germination, photosynthesis, and direction or timing of plant morphogenesis, including flowering and fruiting phenologies (reviews by Endler 1993, 1997, Vázquez-Yanes & Orozco-Segovia 1993, Smith 1995, Fankhauser & Chory 1997, Théry 2000). Because the conspicuousness of colour patterns depends upon the interaction between ambient light and reflectance spectra of colour pattern elements (Lythgoe 1979, Endler 1986, 1990, 1991, 1992, Endler & Théry 1996), ambient light quality will also interact with animal vision systems, and therefore affect visual communication between animals. This can profoundly affect survival and reproduction, as well as communication between animals and plants, crucial to pollination, seed dispersal, and herbivory (Endler 1993, 1997).