biologia - Studia

A. KONTER
started in March and waited 28-33 days before receiving a first egg. One platform
was started in the first decade of April and clutch initiation was 21 days later.
Three platforms appeared in the second decade of April and waited 2, 7, and 15
days before egg laying started. The nest with clutch initiation on the average date
appeared in early April and held its first egg 13 days later. For the 3 early clutches,
the platforms appeared in March, 1 st and 2 nd decade of April and egg laying started
respectively 20 days, 20 days and 5days later.
Nine of the 10 nests with small clutches were clumped with at least 3 other
nests (Table 5). The last nest, already built towards mid-March in 2003, held 2
eggs and was not clumped. It was located within rather poor stands of Reed and
had the nearest neighbour at 3.65 m. Clutch initiation occurred a bit more than one
month after platform initiation.
Table 5.
Total number of full clutches with one or two eggs (small clutches) versus number
with more than five eggs (large clutches) in relation to nest clumping 2003-2006.
Reeds
Bulrush
Number of clumped nests
Number of
clumped nests
0 0 0 0 0 5 6 7 8 0 1 2 >3
Small-large 1-1 0-0 0-1 6-2 0-2 1-1 0-6 1-2 1-2 1-0 2-0 2-0 0-0
clutches
Total clutches 16 16 34 42 35 29 35 19 11 18 22 41 66
% that are small 6.7 0 0 14.3 0 3.4 0 5.3 9.1 5.6 9.1 4.9 0
clutches
% that are large
clutches
6.7 0 2.9 4.8 5.7 3.4 17.1 10.5 18.2 / / / /
In total 5 small clutches were counted in the Bulrush zone (Table 5). The
average clutch initiation dates were quite variable over the 4 years and they were
25 April 2003, 25 April 2004, 16 April 2005 and 19 April 2006. The average
numbers of waiting days from platform to clutch initiation inside the Bulrush for
all years combined were 21 days for March platforms, 11 days for first decade of
April platforms, 5 days for second decade of April platforms and 4 days for later
platforms. With respect to these dates, 2 small clutches were initiated later and 3 on
the average dates. For the 2 late clutches, the platforms were started in March and
in the third decade of April and they waited for 31 and 6 days before holding an
egg. For the 3 others, 2 platforms appeared in March and needed 26 and 39 days
before egg laying was started, the other was built in the second decade of April and
received a first egg within 2 days. The five small clutches were recorded in nests
clumped at degrees 0 (n=1), 1 (n=2) or 2 (n=2).
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