1 Many people find that boxes with a 1.25 or 1 1/8 hole restrictor on them before an egg is laid are not utilized, even by smaller birds like titmice and chickadees. 2  If the entrance hole is enlarged (e.g., by woodpeckers or chewing rodents), put a hole reducer on it.
The Doppler effect widens the spectral lines of rotating objects because the wavelengths changes from blue or red. Blue-shifted, red-shifted, and non-shifted photons mix together to get how its rotating.
Christian Doppler: Christian Doppler, Austrian physicist who first described how the observed frequency of light and sound waves is affected by the relative motion of the source and the detector. This phenomenon became known as the Doppler effect. Educated at the Polytechnical Institute in Vienna, Doppler became