Spring Crane Grus grus migration through Gallocanta Spain II. Timing and pattern of daily departures.

Abstract

The relationships between the daily pattern of Common Crane Grus grus migration departures from a staging area and variables related to weather and number of birds were studied during 1984 and 1985 (totalizing 30 days with migration) using multivariate statistical analysis. Cranes left the roost to the foraging areas between 0628 and 0715 hours. On 95% of the days with migration, the departure lasted only 71-111 minutes, generally between 0900 and 1200 hours. The timing of departure was highly correlated with air temperature at departure initiation: cranes departed earlier with higher temperatures, probably as soon as thermal updrafts had developed and facilitated soaring flight. When the number of birds departing was higher due to favourable weather conditions, the departure evenness, flock size and number of flyways used increased, and the departure interval was slightly extended through an advancement of the initial time of departure.