Wildfowl 63 - page 103

Pitfalls of surveying breeding geese 97
©Wildfowl & Wetlands Trust Wildfowl (2013) 63: 90–104
11 pairs (i.e. 22 individuals with broods,
method I in Fig. 3), observed on 18 April.
This constitutes only 25% of the apparent
number of nesting pairs.
Numbers breeding at other study sites and in 2012
Data from 2012 and from the other two
breeding sites gave similar results, with the
number of territorial pairs recorded during
the spring counts being 60–75% of the
number of nesting pairs estimated from
counts during nest visits. The number of
pairs accompanied with broods at the other
sites in 2011 represented at least 30% (20%
when only broods recorded simultaneously
were taken into account) of the number of
nests. In 2012, much lower numbers of
broods were recorded during the less
frequent (once every two weeks) surveys:
10–25% of the estimated number of
nesting pairs were found to have broods on
following individual families over several
count days; 10–13% when considering only
broods observed simultaneously.
Canada Goose
Breeding phenology at Lake Uettelsheim in 2011
Up to mid-March, Canada Geese were only
observed as pairs or single individuals at
Lake Uettelsheim (Fig. 4). From the end of
Figure 4. Phenology of numbers of Canada Geese counted at Lake Uettelsheim, Duisburg, in 2011,
separated according to status and age-groups. Numbers below the x-axis refer to the total numbers of
goslings counted. Also given is the size of the breeding population (expressed as the number of
apparently paired individuals), derived from four different methods: I number of broods observed
simultaneously, II total number of broods when taking age-differences of broods into account, III
territorial pairs and IV number of nests found (see text for further explanation).
I
II
III
IV
5
0
5
10
15
20
25
30
01-Mar 14-Mar 24-Mar 04-Apr07-Apr11-Apr15-Apr18-Apr21-Apr25-Apr28-Apr03-May06-May09-May12-May16-May19-May24-May27-May31-May07-Jun 16-Jun24-Jun01-Jul10-Jul 21-Jul
Number of individuals
Parents Paired Paired with nest
Breeding / guarding Single birds / flocks Goslings