Alonso J.C., Alonso J.A., Cantos F.J. & Bautista L.M. (1990) Spring Crane Grus grus migration through Gallocanta Spain i. Daily variations in migration volume. ARDEA 78 (3): 365-378

The relations between numbers of Common Cranes Grus grus departing on spring migration and weather, progress of season and course of migration were studied at Gallocanta, NE Spain during February-March 1984 and 1985. Rain, cloudiness and strong headwinds were important factors inhibiting migration. Most cranes migrated in association with the southwestern sector of a high or in the warm sector of a low. Given these fair weather conditions, the number of birds departing was mainly correlated with date and with the relative number of cranes that did not migrate the previous day, but not with the number of birds staging and only slightly with the number that arrived the previous day. The average staging period estimated for an individual crane (5-8 days) was longer than the average duration of adverse weather period without migration (0-3 days). The daily departure never included 100% of the staging birds (mean 14,3%). These facts suggest that the duration of the staging period results from a compromise between the urge to arrive in time at the breeding areas, the inhibiting effect of bad weather, and the tendency to stay longer so as to benefit from favourable feeding conditions.