Sand Martin Nesting in Cast Iron Pipe

We were amazed to see a Sand Martin dive into a cast iron pipe sticking out of the embankment of the River Wear on our recent visit to Durham. Intrigued we watched as a bird arrived and then quickly left every 2 or so minutes. Clearly the birds had a nest with young, and fortunately the pipe no longer functioned as a drain. The birds didn't seem disturbed by people standing on the footpath 2 feet above their nest whilst feeding bread to ducks in the river below.

I tried many times to photograph the bird coming into feed its young, trying to anticipate the focus point. These are my best efforts, taken at 1/1250 sec, only just slowing down the action.

Arrival at the pipe, before flying off.

Occasionally the bird would disappear into the pipe for a minute, possibly to clean the nest. This time it peeped out first to check that the way was clear and safe, before flying off.

Later we discovered another cast iron pipe with yet another nest in use by sand martins. Perhaps in Durham we have discovered a sub-species, the Cast Iron Martin!