divided between seasons and locations, providing the possibility of using stable
isotopes to make a crude map of movements.
7.3 Migration behavior and strategies
The process of migration is typically divided into periods of refueling and flights
between consecutive stopovers. Even though the flights are sometimes spectacular
because of their length and altitude, they only take about one-seventh of the total
migration time in small passerines (Hedenström and Alerstam 1997). Flight is
energetically very expensive but due to the relatively fast transport, and hence short
time required, only about one-third of the total energy consumption is flight cost,
while the remaining two-thirds is spent while on the ground (Hedenström and
Alerstam 1997). Studies on the timing of migratory flights, flocking, flight direc-
tions, speed, and wind drift, are often carried out at migration hotspots where large
numbers of migrants can be observed. As always, the question asked dictates the
method used. Because the overall speed of migration is to a large extent determined
by the rate of energy accumulation (Alerstam and Hedenström 1998), we often
want to monitor the rate of mass (fuel) gain and stopover duration of individual
birds. Information used for orientation and navigation is probably gathered before
flight departure, and hence behavior pertaining to orientation can be obtained
using caged or radio-tagged birds. In this section we present some widely used
methods for study of the behavior and physiology of migrating birds.
7.3.1Counting and observing migrants
Terrestrial birds tend to migrate over land as far as possible and therefore con-
centrate at certain migration hotspots before inevitable sea-crossings or narrow
land bridges. Examples of such locations where masses of migrants concentrate
are Panama, Falsterbo in Sweden, Gibraltar, Bosphorous in Turkey, and Eilat in
Israel. Daily counts of migrating birds passing such hotspots reveal the seasonal
timing of migration among species. Concentrations of migrants also occur at
inland sites where birds follow leading lines in the landscape (mountains, lake-
shores, rivers, etc). Ageing and sexing of birds on the wing (possible in many
raptors; Kjellén 1992) provides information on differential migration and
timing among sex and age classes. Annual migration counts over many years are
also used to monitor population numbers.
Moon watching is a low-tech method to record direction and intensity of
migration, where an observer uses a telescope to register nocturnal migrants passing
the face of the moon. By recording entry and exit of bird silhouettes as if the moon
Migration behavior and strategies| 165