On Friday morning it was snowing when I arrived at Farnborough North. As I walked over the bridge I was surprised to see 6 cormorants perched in the tall tree on the Farnborough side of the large lake. This is the largest number of these birds I have seen on these lakes. Then I saw that the lake was almost completely frozen over: only two small areas remained unfrozen and both of these were crowded with ducks and geese. One of these unfrozen areas happened to be just under the tree that the cormorants were in.
I suppose that it is possible that all 6 cormorants have been on lake for the past few weeks or months, and that I have not noticed them all because they were widely dispersed over its surface, busy fishing. Now the ice has forced them off the lake and into the tree, their true number is obvious. Also, with the smaller lakes freezing over before the larger ones, the cormorants from surrounding lakes may have been progressively forced to the big lake.