The focus is towns and cities in this week's programme, with a report from North America about their largest Swallow, the Purple Martin. Purple Martins are totally dependent on human habitation east of the Rockies for nest sites. West of the mountain range they largely nest in their ancestral way using abandoned woodpecker cavities. As we clear land to build the world's towns and cities what is the impact on the natural world and are there ideas to embrace wildlife in built environment planning? Monty speaks with leading environmentalist Chris Baines and Kate Henderson, the Chief Executive of the Town and Country Planning Association (TCPA).