The common house martin is a migrant which moves on a broad-front (i.e. European birds are not funnelled through the short sea crossings used by large soaring birds, but cross the Mediterranean and Sahara). While migrating they feed in the air on insects, and they usually travel in daylight. Migration brings its own hazards; in 1974, several hundred thousand birds of this species were found dead or dying in the Swiss Alps and surrounding areas, caught by heavy snowfall and low temperatures. Adult survival on autumn migration depends mainly on temperature, with precipitation another major factor, but for juveniles low temperatures during the breeding season are more critical. It is anticipated that since extreme weather is predicted to become more frequent with climate change, future survival rates will depend more on adverse weather conditions than at present.