biologia - Studia

PLATFORM INITIATION, CLUTCH INITIATION AND CLUTCH SIZE IN COLONIAL GREAT CRESTED GREBES
Clutch initiation dates of all small clutches fell twice into the first decade
of April, 5 times into the second and 8 times into the third. Thus, the number of
small clutches goes seasonally increasing (Table 6).
Platform
Initiation
(D=decade)
Table 6.
Summary of characteristics associated with small clutches in the Reeds
and in the Bulrush.
Clutch initiation with respect to average date for the colony
Earlier On the average date Later
3 4 8
Waiting time from
platform to clutch
initiation
Below Above
average average
Waiting time from
platform to clutch
initiation
Below Above
average average
Waiting time from
platform to clutch
initiation
Below Above
average average
March 1 2 3
1D April 1 1 1
2D April 1 1 1 2
3D April 1
Total 1 2 1 3 1 7
Exceptionally Large Clutches
All 17 full clutches with more than 5 eggs were laid in the Reed zones and
none of them was recorded in 2003 (Table 5). 16 of these clutches were started
prior to the average laying date for the Reeds, 13 of them more than 5 days earlier,
the other 3 just 1 or 2 days earlier. The 17 th clutch was initiated on the average
date. 10 of the really early large clutches knew a platform initiation in March and
they waited for 4, 6, 11, 12, 12, 17, 18, 20, 20 and 20 days before receiving a first
egg. 2 platforms appeared during the first decade of April and waited for 6 days
each before initiating a clutch and one platform was started during the second
decade of April to hold an egg 3 days later. For the 3 clutches initiated just prior to
the average date, one platform appeared in March and received an egg after 26
days, the remaining 2 were initiated in the first decade of April and held an egg 5
and 10 days later. The only clutch started on the average day knew its platform
initiation during the second decade of April and a clutch initiation 4 days later.
15 of the 17 clutches (88%) occurred in nests clumped with at least 3 other
nests and 10 (59%) in nests clumped with at least 6 additional nests. One nest
holding a full clutch of 6 eggs was located in a narrow part of Reed I. It was
clumped with 2 other nests and had its nearest neighbour at 2.3 m. The platform
started on 25 March 2005 received its first egg on 5 April. The last platform was
located at the beginning of Reed II where the stands of vegetation were much
spaced and therefore prohibited having very close neighbours. It was started on 20
53