Rare pattern observed in migrating common swifts

Date:
September 15, 2020
Source:
Lund University
Summary:
Compared with other migratory birds, the common swift follows
a very unusual pattern when it migrates from the breeding areas
in Europe to its wintering locations south of the Sahara. This is
what researchers have observed in a major eleven-year international
study of the birds.



FULL STORY ==========================================================================
"Our study is very significant for understanding how organisms, in this
case the common swift, can migrate from one part of the world to another,
where access to food is much better at a given time," says Susanne
AAkesson, professor at Lund University and principal investigator of
the study.


========================================================================== Common 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. Hence the
term chain migration, as opposed to the much more common pattern known
as leap-frog migration, in which 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.

The common swift is the most mobile terrestrial bird in the world. When
it is not breeding, it spends 24 hours a day airborne, for a total of ten months a year. According to the researchers, this has contributed to the species developing its unique migration pattern. Life in the air means
that the swifts need a steady supply of energy and therefore food in the
form of insects. This explains why the southern European populations
migrate even further south in Africa when food availability increases
there in the second half of the wintering period. It also explains why
they are larger than their relatives from northern Europe. Quite simply,
they make sure always to be in the region with the greatest availability
of insects.

The researchers identified another factor determining the development
of the common swift's chain migration: they cannot claim a territory in
the same way as birds that spend more time on the ground.

"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. The common swift is unique in spending ten
months in the air," says Susanne AAkesson.

"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 -- they have a lifespan of over 20 years," she continues.

The researchers tracked 102 common swifts (Apus apus) from eleven
different populations that nest in Europe, from Swedish Lapland in the
north to Spain in the south. Using micro data-loggers attached to the
birds, which record data including time of sunrise and daylight duration,
they were able to calculate longitude and latitude and thus to determine
the location of the 102 individuals at various times during the year. The
study involved researchers from 14 universities and bird conservation organisations.

Chain migration has previously only been observed in two species: the
sharp- shinned hawk and the northern gannet.


========================================================================== Story Source: Materials provided by Lund_University. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. S. AAkesson, P.W. Atkinson, A. Bermejo, J. Puente, M. Ferri,
C.M. Hewson,
J. Holmgren, E. Kaiser, L. Kearsley, R.H.G. Klaassen, H. Kolunen, G.

Matsson, F. Minelli, G. Norevik, H. Pietia"inen, N.J. Singh,
F. Spina, L.

Viktora, A. Hedenstro"m. Evolution of chain migration in an aerial
insectivorous bird, the common swift Apus apus. Evolution, 2020;
DOI: 10.1111/evo.14093 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200915105949.htm

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