98 Pitfalls of surveying breeding geese
©Wildfowl & Wetlands Trust
Wildfowl
(2013) 63: 90–104
March onwards, guarding males were seen
around the breeding island, and in April
incubating females were also observed from
the banks of the lake. The first goslings
appeared in the first days of May. On 6 and
12 May, no broods could be found, but
during later visits these broods were
identified by their age and plumage
characteristics. Only one gosling reached the
age of six weeks, and then disappeared.
Fledging success therefore was apparently
zero. Few Canada Geese were classified as
non-breeders during the surveys, and these
congregated with the unsuccessful breeding
pairs during May. In contrast to Greylags, all
Canada Geese stayed around the breeding
site after losing their broods. A marked
immigration of birds during moult
(observed for Greylag Geese at the site) was
not recorded for the Canada Geese.
Numbers breeding at Lake Uettelsheim in 2011
A nest count on 11 April found 15 active
nests on the island, indicating 30 breeding
adults (method IV in Fig. 4). Some of the
nesting Canada Geese had taken over old
Greylag nests after their eggs had hatched.
Territorial behaviour (including guarding
males), suggested nine territorial Canada
Geese pairs at Lake Uettelsheim (
i.e
. 18 adult
individuals; method III in Fig. 4), based on a
count of three pairs, four pairs with a nest
and two guarding males around the breeding
island on 4 April,
i.e.
60% of the apparent
nesting pairs. Only three pairs (
i.e.
six adult
individuals) were observed simultaneously
with goslings on 3 May (method I in Fig. 4).
One more pair with recently hatched
goslings was seen on 16 May, suggesting
four pairs with goslings in total (Method II
in Fig. 4). Thus 26% of the number of
apparent nesting pairs was recorded with
young (20% when using only the maximum
number of broods).
Numbers breeding at other study sites and in 2012
At the two other study sites in 2011 and
Lake Uettelsheim in 2012, 50–75% of all
apparent nesting pairs were assessed as
holding territories. In 2011, up to 40% of
them were seen with broods (up to 25%
when only broods observed simultaneously
were taken into account). Data from 2012
from the other two study sites were
insufficient as nest counts of Canada Geese
were regarded as incomplete.
Discussion
Pitfalls of the different survey methods
Despite their size, appearance and
conspicuousness, surveying breeding geese
is a challenge and recommending the most
suitable method has not been made easier by
the fact that, historically, this has been
carried out using different methods, or
a combination of methods. The data
presented here showed radically different
results obtained using different methods
which make comparisons between sites or
between years very difficult based on
different methods. Unfortunately, each of
the methods has its own drawbacks and
their application will also depend on site-
specific and practical issues. Use of
individually marked birds would greatly
improve possibilities to assess the size of a
local breeding population and movements
of broods (Nilsson & Persson 2001;
Kampp & Preuss 2005), but is not possible
