Warmth and safety in numbers for wagtails
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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.
At Christmas time, many of the trees in the city centre are draped with strings of Christmas lights, including this special tree.
But if you visit in the evening, you might think this tree has extra lights or festive baubles, but it is in fact alive with thousands of little black and white birds, Pied Wagtails (Motacilla alba).
This tree is their winter roost. As the evening draws in, birds start to arrive from the surrounding suburbs and countryside, where they’ve been feeding during the day. As they arrive, they flutter onto the tree’s branches, until there are thousands of birds perched among the Christmas lights.
The Pied Wagtail is also called a ‘Willy Wagtail’ and is a common bird most of us recognise by how it frantically bobs its tail up and down. There are a few theories about why this bird moves its tail in this way.
My favourite is that it is showing potential predators that it is fit and healthy, with its very active movements, to make it clear that it wouldn’t make a good option to chase. Another name for this bird is ‘Polly Washdish’ which stems from it being commonly seen in places where people used to wash dishes before they had running water in their homes.
During the day, individual pied wagtails are usually seen searching for insects on their own, making it even more surprising to see such a large group come together in a winter roost. The birds choose to roost together here at Grand Parade on winter nights for many reasons. One is that urban areas are warmer than the surrounding countryside.
The tall buildings, dark surfaces and concrete in our towns and cities mean they retain more heat than natural landscapes, and at night the difference in temperature is even more pronounced.
This means these little birds can conserve more energy overnight here than if they were to roost in the countryside. Reedbeds are a more natural habitat for a Pied Wagtail roost, but the warmth of the city centre attracts them to this street bustling with busy shoppers and night-time revellers.
Another reason some species form large winter roosts is for information exchange. It is believed that the birds notice each other’s weight and physique. And this tells them who it might be worth following the next morning when they head out to feed. A fatter bird is obviously more successful at finding food.
There is also ‘safety in numbers’. By creating dense flocks, many birds — such as jackdaws, rooks, starlings, and geese — individually benefit. Each is less likely to be targeted by a predator.
Hundreds of frantically flapping wings can confuse predators, and there are many more eyes on the lookout for danger through the night.
Choosing an urban location can also reduce predation because there are fewer birds of prey, such as sparrowhawks, which will venture onto this busy street. These pied wagtails are willing to accept the car fumes, twinkling lights and noise of their city centre location for the safety and warmth that such a location provides.
And, of course, this isn’t the only pied wagtail roost in the country. They can be found in urban centres and car parks where conditions are right.
As night draws in, hundreds of pied wagtails cover every twig and branch. Under the noise of traffic and passers-by, if you listen closely, you can hear hundreds of little voices with their 'chissick, chissick' calls as they settle down for the night.
As droves of late-night shoppers pass underneath this tree, I’m sure most are oblivious to this lovely winter wildlife spectacle happening right above their heads, here in the centre of the city.