Competition for Nest Sites between Sand Martins and Coots

Walking along Kennetside this morning, I saw a couple of sand martins (Riparia riparia) flying up and down the river.  This itself is unusual because I cannot remember having seen sand martins before, certainly not since I moved down south in 1988.  Hence I was quite surprised to see them in central Reading. 

On the north side of that part of the river there are several rainwater run-off pipes that stick out from the bank.  At one point, one of the martins swooped down to the mouth of a pipe, but a nearby coot (Fulica atra) raised it head as if surprised, and the martin flew up and away.  Then a few seconds later the sand martin came down again and, this time manage to perch at the entrance of the pipe.  However, when the coot saw this, it flew up, scaring the sand martin away, and  then stood itself in the entrance to the pipe, as if standing guard.  The martins then flew off up the river and, after a little while, the coot flew back down to the water and continued with what it had been doing before the interruption.

I have noticed coots trying to nest in those pipes before, but I don't think any can have succeeded because in heavy rain the flow of water from the pipes is so great that it would easily wash out any nest material.

Update on Fri 2009-06-12 by Tristram Brelstaff

The sand martins are more persistent than I thought.  On two occasions since then I have seen them going in and out of the same pipes, and the coot was nowhere to be seen.