86 Survival and dispersal in a new Barnacle Goose population
©Wildfowl & Wetlands Trust
Wildfowl
(2013) 63: 72–89
populations is surprising. Van der Jeugd
(1999, 2001) concluded that
c
. 25% of all
birds hatched in the oldest and largest
Barnacle Goose colony in the Baltic on
Gotland, Sweden dispersed during a 10-year
study, although natal dispersal was much
more frequent in males than females. Van
der Jeugd & Litvin (2006) estimated that
6.6% of all juvenile Barnacle Geese from
the same colony dispersed over long-
distances, most probably to the Russian
Arctic, a much lower figure than is found
here. Between 2002 and 2008,
c
. 2000
fledgling and adult Barnacle Geese were
colour-ringed in colonies at Kolokolokova
Bay and on the Kolguev Island in the
Barents Sea region. Despite this,
observations of Barnacle Geese hatched in
the Barents Sea population are still lacking
from the Dutch breeding grounds. It is
therefore concluded that dispersal is
probably not balanced by immigration, and
that the Dutch Barnacle Goose population
currently is a source, from which restocking
of the Barents Sea population takes place.
Although this may seem counterintuitive,
the probability of a Dutch-hatched Barnacle
Goose moving from its natal area during its
first winter and on finding a flock of
Russian-hatched congeners, subsequently
joining them on migration to Russia, must
be much larger than the probability of a
Russian-hatched Barnacle Goose meeting a
member of the much smaller Dutch
population.
Apart from dispersal to Russia, dispersal
to northern Germany was frequent, with
both young as well as adult birds dispersing
to sites
c
. 400 km away. This was especially
apparent from the colony in Fryslân, that
was recently disturbed by foxes (Kleefstra
2010; R. Kleefstra, pers. comm.), that may
have prompted birds to start a new life
elsewhere.
Dispersal over distances < 10 km is partly
an artifact of the fact that the location of
ringing does not necessarily reflect the exact
location of breeding. It is therefore likely
that these birds are in fact philopatric. There
is only a very minor risk that birds that were
ringed during moulting at one of the three
localities were in fact breeding or had been
born at localities that were further away. The
two localities at Goeree-Overflakkee are
c
.
10 km apart from each other and serve as
brood-rearing areas for Barnacle Geese
breeding in the same area (Hellegatsplaten)
or at small islets 1–2 km away from the site
(Krammerse Slikken), with little exchange.
All marked birds were either fledglings or
adult breeding birds leading young and
therefore must have hatched or bred
relatively close by. We cannot exclude
completely the possibility that some adult
birds that exhibit long-distance breeding
dispersal may in fact be birds breeding in
Russia and moulting regularly in the
Netherlands, but given the large difference
in timing between the populations (van der
Jeugd
et al
. 2009) this seems highly
implausible. After all, when Dutch birds
start moulting by the end of June, most
Russian birds have just started incubation.
For birds born in the Netherlands and alive
at breeding age that are subsequently
observed along the flyway during spring
migration, and were never sighted in the
Netherlands during the breeding season,
dispersal seems the only explanation
possible.
