Chapter 4 - Weather and migration

Abstract

This chapter is concerned mainly with the effects of weather on bird migration, describing the conditions in which birds prefer to migrate and those in which they normally avoid migrating. Following winds speed birds along their journeys and reduce the energy costs of flight, while opposing winds can increase the costs, and crosswinds can blow birds off course. The ways in which birds avoid or correct for wind drift are explained. The influence of global wind patterns on migration routes is discussed, accounting for some of the detours that birds take on migration. Also discussed are the altitudes at which birds migrate, and whether particular species migrate primarily by night or primarily by day. Conditions which lead some birds to migrate in reverse direction for the time of year are discussed.