How can there be more robins today than there were when the colonists first came to America?
When the colonists first arrived, just about all of eastern America was heavily forested, and there were few trees at all in the prairie. Colonists cleared the forests, making it easier for robins to hunt on open ground, and also introduced more species of earthworms from Europe. In the prairie, they planted trees which robins use for nesting. Q. How do humans affect robin migration? A. When humans used the insecticide called DDT in the U.S., many robins died during spring migration as their bodies metabolized large amounts of body fat at once–DDT from the worms robins ate all winter was stored in their fatty tissues and all released into their bloodstream at once. This was a harmful effect, and now that DDT is banned in the US, is no longer a problem for our robins. Humans also have very positive effects on migration by planting the trees that provide food and shelter for migrants. Q. What are the biggest dangers facing robins? A. Dangers facing robins include (from most dangerous to
