Exhausted Blue Tits

Blue Tits will occasionally pick some very strange places to nest in. This usually happens when natural holes in trees or nest boxes are in short supply. I was visiting one of my birding sites today when I noticed a Blue Tit carrying food towards a pumping station near to where I had parked. I got back in the car to use it as a hide and watched to see where the Blue Tits were going. It wasn't long before a Blue Tit returned with a beak full of caterpillars and landed on some kind of vertical exhaust pipe. It then dropped inside and came out a few seconds later. 

I repositioned the car to get some photos of the birds entering and leaving this unusual nest site. I have seen Blue Tit nests in street lights and uncapped sign posts but this is the first I have seen in an exhaust pipe.

Exhausting work rearing chicks and literally in this case. Sorry I couldn't resist.

I assume the exhaust pipe is part of some equipment that is no longer used or only gets used in certain circumstances. I just hope it doesn't need to be used before the chicks leave the nest.