In the Belgorod
region Common Swifts hunt at different heights at different times of the
day. At noon they hunt between 40 - 50 m and in the late afternoon
between 20 - 30 m (Bulyuk & Chernetsov). In Israel they use the
advantage of thermal upwinds and let themselves be carried high into the
sky (Hahn in litt.). In Sweden and Finland Swifts often fly at
about 3500 m high (Gustafson). During their nocturnal “sleeping flights”
in the breeding grounds in Sweden, they fly with about 8.5 m s-1
airspeed and mostly between 1000 and 2200 m high. They orientate to the wind, to stay as close
to their colony as possible (Bäckman & Alerstam). Whatever the position
of the body, Swifts keep their eyes parallel to the horizon at all
stages of the flight, even the most aerobatic (Tigges).
In Berlin the members of a
colony fly within a definite territory, with the exception of a period
of about 6 - 8 hours each day spent away from the colony area. (Tigges).
In Tel Aviv some Swifts share one
hole for access to their different nests (A.Bear pers. com.). In
Holland they enter their nests at 70 km/h (v. Arkel). In Nîmes Swifts
seem to be sensitive to noise: they breed better in the quiet backyard
of a museum than in nests facing a noisy street (Gory). In Italy males
take a smaller share in caring for young (Carere & Alleva) and parents
eat the faeces of their chicks (Dell'Omo et al.). In Pavia the Common
Swifts prefer to occupy nesting sites between 9 - 14 m high, the
exposure to the sun is not a significant factor in nest-hole selection
(Colombo & Galeotti), in Lanzhou the preferred height is 8-20 m (Wang after Yuan).
In the Spessart the holes in Oaks must be 20 cm diameter at least and be
exposed to the sun to be used by them for breeding (Zahner). In Lanzhou
there is room for only one adult on the nest (Wang after Yuan).
Research in Switzerland on different types of nest boxes showed that
insulation of the boxes or nests has nearly no effect. Boxes on the west
facing sides of houses in sunshine got less hot than those on the east
facing side. Nest bricks were of no use, because they got too hot. Nest
sites facing north or at sites with no direct sunshine were always safe
(Knuchel & Weber).
The well known “see-wee” calls of the
Common swift are largely decoded. They identify the sex of the caller
(the higher pitch is from the female, the lower one from the male)
(Kaiser). Exposed as group calls (“screaming parties”) they show the
claim of the territory of the colony (Tigges). Four different groups of
Common Swifts live on the banks of Lake Geneva, the "faithful breeder",
the "young breeder", the "pre-breeder" and the "young banger". Each
group shows specific behaviour and can be clearly differentiated by
their time of arrival. The "pre-breeder" takes a good month to find a
nesting place and a partner. The "young banger" flies into a nest site
only exceptionally (Genton).
Does the aerial copulation
result in insemination? Sometimes one can see that one bird flies on top
of another, and for a second both individuals look like one bird with
four wings. In Oxford DNA surveys of chicks showed that 4,5% of them did
not descend from the father that was hatching and feeding them. Common
Swifts fight a same-sex individual vigourously if it enters the nest
area, and so these offspring may be the result of such aerial
copulations (Thaís et al.).
Common Swift chicks in Spain achieved a far better weight at fledging,
when they were fed predominantly with crickets, than their brothers and
sisters which were fed with minced rat meat. (Fusté). In Oxford
nestlings prepare themselves for fledging with the help of push ups (Markman
et al). In Kronberg they fledge at late dusk (Kaiser) and in Sweden
young Swifts sometimes roost in trees (Holmgren).
The migrating Common Swifts
above the Balearics come from Algeria and fly most often during the
night, especially in the first, eighth and ninth hour after sunset. The
Balearic Isles do not lie on a migration route at all, but the Common
Swifts seem to cross the Mediterranean at about 8,9 m s -1
airspeed everywhere (Speich). In Spain however they prefer routes along
the east coast (Gordo). The Common Swift is a long distance migrant and
does not react to global warming, the arrival dates for vast parts of
Europe have not changed over a period of up to 250 years (Tigges). But
there are periodical shifts forth or back of 15-20 years (Gordo,
Lehikoinen in litt).
In Germany the
principal parasite of the Common Swift, the Swift louse fly (crataerina
pallida) does not cause harm, neither to the parent Swifts, nor to
the chicks; at least in terms of brood success (Walker pers. com.).