Above: The researchers tracked 102 swifts (Apus apus) on their journey to Africa, from 11 different populations that nest in Europe, from Swedish Lapland in the north to Spain in the south. Micro data-loggers attached to the birds allowed researchers to calculate longitude and latitude, and determine the location of the birds at various times during the year. Photo: Aron Hejdström

 

A MAJOR 11-YEAR international study has found that swifts follow an unusual pattern when migrating from their breeding areas in Europe to their wintering locations south of the Sahara. 

Most migratory birds follow a migration pattern known as leap-frog migration, where the populations that arrive first in a location claim the territory and occupy it, forcing populations that arrive later to leap-frog over the occupied area and fly further. But researchers at Lund University have identified a different pattern used by swifts (Apus apus), which they term chain migration.

Swifts that nest in Sweden and northern Europe arrive in sub-Saharan Africa four to six weeks later than the swifts that nest in southern Europe. By that time, the southern European swifts have already migrated even further south on the African continent.

“The core reason why the common swift engages in chain migration, whereas almost all other birds such as songbirds, ducks, geese and waders have leap-frog migration patterns, can probably be found in the amount of time they spend airborne,” said Susanne Åkesson, professor at Lund University and principal investigator of the study.

The swift spends 10 months in the air. When it is not breeding, it is airborne 24 hours a day. Researchers believe this has contributed to the species developing its unique migration pattern.

The birds rely on a steady supply of energy which is gained through eating insects. The southern European swift populations migrate even further south in Africa when food availability increases there in the second half of the wintering period. According to researchers, this also explains why they are larger than their relatives from northern Europe.

“I think it is amazing that they know where food is to be found and when they should head for that specific location. They migrate over continents in such a way as to ensure continuous access to food and thereby to survive,” continued Ms Åkesson.

The study is published in the Society for the Study of Evolution’s journal Evolution.

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