Warmth and safety in numbers for wagtails

The birds also notice each other’s weight and physique when they meet up to find out who it might be worth following the next morning when they head out to feed

A pied wagtail peeps down from a wall. During the day individual pied wagtails search for insects on their own but typically come together in their hundreds at night to roost. Picture Denis Minihane

Some years ago, I worked with the excellent wildlife filmmakers Crossing the Line, on a TV series called ‘Wild Cities’. My job was to research urban wildlife stories and locations in Cork and Dublin.

One of my favourite scenes from that series centred around a very ordinary street tree on Grand Parade in the centre of Cork city. There is a row of London Plane trees on Grand Parade which all look identical. During the day, this tree, outside Lloyds Pharmacy, looks the same as any other on the street. But after dusk, something magical happened.