Chapter 8 - Speed and duration of journeys

Abstract

This chapter focuses on the speed and duration of journey of birds. Depending on the distance traveled, a one-way migratory journey can last for several hours up to several months, including resting, fueling, and flight times. Some species that migrate long distances between northern and southern hemispheres spend around half of each year on migration. When radio-tagged migrating birds are followed in a small airplane, considerable detail about day-to-day behavior can be obtained, in addition to measures of speed. Turning to species that migrate by soaring–gliding migration over land, many species of raptors have been fitted with radio-tags and monitored by satellite on their journeys. The ratio of flight to stationary time during the migration periods of small passerines is typically around 1:7, matching theoretical predictions, and in larger species that travel by flapping flight the ratio is around 1:14–1:30, as large species have relatively higher flight costs than small ones, and take longer to accumulate the necessary body reserves. Some pelagic seabirds travel even faster, with mean speeds up to 950 km/day recorded from albatrosses. In some species that travel by flapping flight, fueling times associated with large body size may make it impossible to breed, moult, and migrate long distances within one year, and could thereby limit migration distances (and hence geographical ranges).