dispersal of ticks and tick borne diseases by birds - Lista fuglestasjon

would also be important for transport of
ticks, as red deer, roe deer and moose,
altogether counting about 100,000
individuals (Andersen et al., 2010), have
yearly migratory ranges of 200, 100 and
50-60 kilometers repectively (Reimers,
1990). Although these animals may
reach coastal island by swimming,
transport by birds would be needed to
cross oceans. Birds are commonly
parasitised by the immature stages of I.
ricinus, and can easly cross geographical
barriers, and they occur in enormous
numbers (Table 1).
Bird Migration
Bird observatories, mainly manned by
volunteers, monitor the bird migration
by observation and ringing. Recovered
rings, on dead or recaught birds, give
data for the birds’ movements. The Lista
bird observatory is situated on a
promontory of the southwestern
Norwegian coast. The Store Færder and
Akeröya bird observatories are situated
near the inlet of the Oslo fjord, about 20
km from each other, while Jomfruland is
about 60 km SW of Store Færder (Figure
1 in Paper III).
There are between 30,000,000 and
85,000,000 migratory passerine 5
birds in
Norway (Table 1). During spring
(northward) migration most of the
species, such as the robin (Erithacus
rubecula), redstart (Phoenicurus
phoenicurus), song thrush (Turdus
philomelos) and willow warbler
(Phylloscopus trochilus), follow a
western pathway along the Atlantic
coast. Birds heading for Sweden follow a
more eastern parallel northeastern route
(Fransson and Hall-Karlsson, 2008).
Therefore, few of the species that follow
the Atlantic coast migrate via Sweden.
Norwegian blackbirds (Turdus merula)
5 Passerines are birds belonging to the order
Passeriformes. In Northern Europe, all passerines
belong to the suborder Passeri (oscines).
Passerine birds are also called “perching birds”
or “song birds” (including crows). Only
passerine birds are included in this project.
19
mainly winter on the British Isles and may
migrate directly over the North Sea or via
continental West Europe (Wernham et al.,
2002). The Sylvia warblers migrate broadly
across the Alps and may either cross the
Skagerrak Sea via Denmark or follow the
Swedish coast (Bakken et al., 2006). A few
species have an eastern migratory route, such
as the white wagtail (Motacilla alba), which
may migrate through Denmark or Sweden,
and the bluethroat (Luscinia svecica), which
has a strictly eastern route. The Norwegian
redpoll (Carduelis flammea) may spend the
winter from England to Russia, but it seems
that the nominate subspecies, flammea,
migrate to the east, while the subspecies
cabaret migrate to the west (Bakken et al.,
2006). In this study, the ratio of
flammea/cabaret was 4/183 at Lista and
57/115 at the three more eastern bird
observatories.
However, most birds arriving at the four bird
observatories included in this study have to
cross at least 112 km of open water.
Therefore, these four bird observatories offer
a unique opportunity to study the transport of
ticks across a geographical barrier. A typical
day distance during migration may range
from 40 km/d (blackbird) to 90 km/d
(redstart) (Bakken et al., 2006). However, if
needed, the birds can traverse much larger
distances. Blackbirds that winter on the
British Isles have to cross at least 500 km
over the North Sea. At a flight speed of 47
km/h (Meinertzhagen, 1955), it takes more
than ten hours of non-stop flying to reach
Lista on the other side.
The three eastern study locations are situated
north of Jutland (see map, i.e., Paper III,
Figure 1). Migratory passerine birds will
follow land when possible, to rest and eat.
Therefore, most of the birds arriving at
Jomfruland, Store Færder and Akeröya will
have to come via Jutland. There would be a
negative selection for heading for Lista,
compared to heading north when leaving
Jutland, as there is a risk of not finding land
at all, but still, many birds that are ringed at
Jutland and continental Europe are recovered
at Lista (Bakken et al. 2006). This could be