As per a new study, migrating birds travel faster and put extra effort into staying at course in spring than in fall. Researchers found that the birds speed up during spring because arriving late to their breeding grounds can affect their reproductive success. Past studies have shown that migrants take shorter breaks in spring, but it is harder to tell whether they also move faster in the air. Researchers at the University of Oklahoma in the US used high-tech weather surveillance radars and found that birds did indeed fly faster in spring and compensated more for crosswinds that could blow them off course. Bird migration is the regular seasonal movement, often north and south along a flyway, between breeding and wintering grounds. Many species of bird migrate. Migration carries high costs in predation and mortality, including from hunting by humans, and is driven primarily by availability of food. It occurs mainly in the northern hemisphere, where birds are funnelled on to specific routes by natural barriers such as the Mediterranean Sea or the Caribbean Sea. Historically, migration has been recorded as much as 3,000 years ago by Ancient Greek authors including Homer and Aristotle, and in the Book of Job, for species such as storks, turtle doves, and swallows. More recently, Johannes Leche began recording dates of arrivals of spring migrants in Finland in 1749, and scientific studies have used techniques including bird ringing and satellite tracking.