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.
The Earth is in motion relative to the star because it are orbiting the Sun, so you have to take the Earth's orbital motion into account when figuring the star's velocity from the doppler effect. Also, the doppler effect gives you only the speed along the line of sight. Most stars move at an angle to our line of sight.