SHORT COMMUNICATIONS 
161 
involved only a minority of a group. Active 
vocalization may have helped group cohesion, hut 
il could not be distinguished from advertising by 
solitary birds or from contact calling by partners 
momentarily separated. 
It is not known to where the departing 
grebes flew and whether they targeted breeding 
areas in the region or flew a long distance. Eared 
Grebes can move to other sites used for breeding, 
even after arrival in a breeding area, or emigrate 
from the region (Cullen 1998). It is also unknown 
whether the grebes departed in flocks from the 
English Channel and whether they headed in one 
or different directions. 1 assume they were 
migrants and the extent of their pattering flight 
maneuvers suggests an eagerness to move on. 
The counts of 25 and 26 May show that not all 
Eared Grebes had left the English Channel over 
night. Grebes present in the NS part were not 
observed on 25 May and they may not have 
engaged in group pattering. The first count on 26 
May showed that low numbers of grebes were 
present inside the EW canal and the higher later 
count suggests that new grebes were continuously 
settling there. Over 200 Eared Grebes left the 
English Channel during the night and this number 
corresponds as an order of magnitude to the 
numbers involved in the group pattering. Thus, 
most pattering grebes could have left over night 
iUlt l it is likely their zugunruhe contributed to a 
simultaneous departure. They were gradually 
replaced by conspecifics moving into the EW 
fanal on the following day. 
Eared Grebes often do not arrive within a short 
lJ P se of time inside a breeding region where 
numbers generally build up over several weeks. 
% synchronize, however, nest establishment 
McAllister 1956. Boe 1994). In this context, it is 
01 interest to further investigate how a conspic- 
uous pre-migratory group pattering as observed at 
Tule Lake Refuge may contribute to a coordinated 
'inward flight inside a breeding region that would 
facilitate simultaneous colony establishment by 
•urge numbers of pairs. Unfortunately, the data 
from Tule Lake Refuge do not permit any 
conclusion to be drawn. 
ACKNOWLEDGMENTS 
I am grateful to Michele Nuss from the Tulc Lake Refuge 
Headquarters who was of great help in the preparation of 
my fieldwork. 1 thank J. R. Jehl ,lr and C. E. Braun for 
critical review and constructive comments on the first draft. 
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