This is BirdNode.

Many people think that evolutionary change occurs so slowly, we cannot observe it directly.

Not so. For example, today in the US, house finches are evolving rapidly and visibly.

In 1941, some captive house finches from California escaped near New York City.

They spread rapidly and are now found across most of the United States and in southern Canada.

Many of these areas have cold snowy winters during which many birds die.

The finches have evolved because those that survive differ from their parents.

Size is one example.

Male house finches in recently established populations in Michigan and Montana are larger than the males that escaped.

Large males outcompete small males for food so are more likely to survive the winter.

They also pair more successfully with females early in the spring.

Smaller females survive better than larger females as nestlings.

Also, because they need less food to maintain their own bodies, they can breed earlier in spring.

Females that breed earlier raise more young than those that start breeding later.

Rapid evolution of house finches reminds us that evolutionary changes are occurring visibly all around us.

For Bird Note, I'm Michael Stein.