You will now listen to part of a lecture. You will then be asked a question about it. After you hear the question, you will have

"Brood parasitism" is the practice some bird species have of laying their eggs in another bird species’ nest, leaving the host family to raise their young. The most common example of this in the American West is the cowbird. Naturally, where this sort of behavior is common, other species have developed defenses. Let’s consider two of these.
The first is changing habits. Some bird species such as robins do not commonly guard their own nests. But when other birds are observed in the area, robins suddenly become vigilant with one mate or the other constantly in close proximity to the nest. This prevents other species from laying their eggs in the robins’ nest.
Another defense, a good deal less voluntary, is for a bird species to lay eggs of a distinctive size, shape, or color. Since birds generally have good vision and are color sensitive in contrast to most mammals, this is a highly effective defense against brood parasites. This defense is displayed, among other species, by the American coot. When eggs of the wrong color, size, or shape are introduced into the nest, the birds waste little time in pushing the interlopers out. In this way, the parasite species is thwarted.