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Minus 1: Tree for Two

Hummingbirds usually lay two eggs. One scientist studied 77 Ruby-throated Hummingbird nests. He found that 66 nests had two eggs, 10 nests held only one egg, and one nest had three eggs.

Q. Why do you think hummingbirds almost always lay two eggs? (Answer below photo.)

Photo: Dorothy Edgington

A. One egg is not the best number for hummingbird nests. If anything happens to one baby or the egg doesn't hatch, all the work and energy the mother put into building the nest and incubating will be lost. But more than two eggs take too much energy from the mother. She would have to use more body heat to warm the eggs. She'd need so much food to feed three babies that she might grow too weak. If weather conditions were great and food abundant, a nest of three babies could survive — but it's a very big risk.