White birds, such as egrets and ibises, often hang around cows because they can benefit from the insects that the cows stir up as they graze. These birds will often perch on the backs of the cows or walk alongside them, waiting for the cows to disturb insects from the ground. The birds can then swoop down and catch the insects for food. This relationship is mutually beneficial, as the birds help to control the population of insects that can bother the cows.
In addition to providing a source of food, cows can also provide protection for white birds. The large size of the cows can deter predators, and the birds may also benefit from the cows’ body heat. In some cases, white birds have even been known to nest in the fur of cows.