Pitfalls of surveying breeding geese 91
©Wildfowl & Wetlands Trust
Wildfowl
(2013) 63: 90–104
In recent decades, numbers of breeding
geese, notably Greylag Goose
Anser anser,
have shown exponential increases at many
sites throughout central and northwest
Europe. In addition, introduced species
such as the Canada Goose
Branta canadensis
and Egyptian Goose
Alopochen aegyptiaca
have increased their breeding range and
established thriving breeding populations in
many regions (Allan
et al.
1995; Madsen
et al.
1999; Blair
et al.
2000; Geiter
et al.
2002;
Rowell
et al.
2004; Kampp & Preuss 2005;
van der Jeugd
et al.
2006; Austin
et al.
2007;
Fox
et al.
2010; Kowarik 2010; Rehfisch
et al.
2010; Gyimesi & Lensink 2012). These
species not only favour natural breeding
habitat, but may also occur in high breeding
densities in urban and suburban areas such
as parks and sand pits or gravel pits (Wright
& Giles 1988; Rowell
et al.
2004; Kampp &
Preuss 2005; Havekes & Hoogkamer 2008).
Such high goose densities may conflict with
recreational use of parks (especially by
fouling of park lawns by droppings) and
cause damage to agricultural fields (Allan
et
al.
1995; van der Jeugd
et al.
2006; Rehfisch
et
al.
2010). Hence, measures to prevent geese
from feeding in parks and reduce grazing
damage have been discussed and adopted at
several sites (Wright & Phillips 1991; Baker
et al.
1993; Allan
et al.
1995; van der Jeugd
et
al.
2006; Voslamber 2010).
Knowledge of actual numbers of breeding
geese is an important prerequisite for the
appropriate design, implementation and
monitoring of management measures
introduced to reduce such conflicts
successfully. However, surveying breeding
geese is not error-free and Greylag Geese are
particularly regarded as one of the more
difficult species to count effectively, as they
often breed in poorly accessible areas and
local numbers include a varying proportion of
non-breeders (Voslamber
et al.
2000). Hence,
several censuses of breeding geese have
focused on a survey of moulting sites, giving
an overview of total population size, rather
than assess the number of breeding pairs
(Rowell
et al.
2004; Austin
et al.
2007). In this
paper, we report on the comparative results of
breeding bird censuses using different
methods, applied in urban and suburban areas
of Duisburg, Germany, as part of a
population management project there relating
to (reintroduced) Greylag and Canada Goose
populations during 2010–2012. Our aim is to
review the different methods commonly used
in breeding bird surveys (Gedeon
et al.
2004;
Südbeck
et al.
2005; van Dijk & Boele 2011),
and to discuss their applicability in relation to
their accuracy and practical implementation
for ordinary field observers.
Methods
Study area
Censuses of breeding geese were conducted
at three sites in a suburban area on the
western fringe of the Rhein-Ruhr district, in
the municipality of Duisburg (Northrhine-
Westphalia, Germany). The study sites
comprised Lake Uettelsheim, Lake Toepper,
and a complex of Six Lakes at Duisburg-
Wedau (Fig. 1). All lakes were created from
sand or gravel extraction, but are now
mainly used for recreational purposes. At all
three sites, conflicts with recreational
activities occur, because of flocks of geese
fouling lawns and playgrounds with
droppings, and therefore being considered
