A niche refers to how an organism responds to different environmental conditions. This conditions could be competitors and how resources are distributed.
Warbler bird's optimum and tolerance requirements for survival, in terms of temperature, precipitation, and food abundance talks about the Niche of the Warbler bird. The ecologist is therefore trying to study the niche of the bird.
Light is part of a spectrum of electromagnetic energy that includes radio waves, microwaves, infrared radiation, visible light, ultraviolet "light", x rays, and gamma rays. Electromagnetic energy travels as waves that vary in wavelength.