For instance, the Snow Geese who migrated through Omaha on March 14 could have waited another couple of weeks until the lakes opened up and the snow melted. This would have made their migration easier by making available more food and safe roosting, but it wouldn't have allowed them enough time on the breeding ground to maximize breeding success. The length of daylight told them it was necessary to press on, irrespective of the hardship. Factors like food supply and weather may fine tune day length. If Red-winged Blackbirds are experimentally provided with abundant food, they will begin laying eggs three weeks earlier than birds without an abundant supply.
Some species become so specialized in their breeding requirements that extinction looms near.
Others, though more general in breeding strategy, are threatened by the rapid changes brought on by human influences on the environment. This article describes broad concepts about ways in which birds time breeding. At every level, birds have found unique and subtle strategies to accomplish successful breeding.