“What are you doing?” I’d been lurking round the back of Barclays Bank for about 10 minutes when I realised I’d begun to attract attention. In the car park, about 20 yards behind me, a woman stood staring uncertainly at my binoculars. “It’s just that I work at the bank, and …” At that moment a fountain of house martins broke over our heads. The birds frothed around the eaves of the bank. Some shot into the mud nests there, others perched on the outside repairing them, the rest filled the air around us with their joyous twittering. I explained that I was surveying house martins for the British Trust for Ornithology, and that finding such a large colony in our market town of Thirsk was like striking gold. Not only was she satisfied that I was