Migration is a big part of bird behaviour through the autumn. It often involves birds heading south for the winter. Swallows and Cuckoos heading to various parts of Africa for example. Some birds are here all year though, but are found in different habitats in different seasons.

Black-headed gull is one of the species which is here all year. There are breeding colonies of hundreds of them not far away, at RSPB St Aidans and another in the Dales near Skipton. In the winter, gulls often roost overnight on reservoirs with thousands (probably tens of thousands) at Eccup Reservoir, north of Leeds. Are these the same individuals, moving short distances from those summer breeding colonies to local fields and parks where they can be seen in winter pulling worms? Actually, it’s more complex than that, with different populations of Black-headed gulls migrating great distances between seasons.

We know about movement and lifespan of birds from ringing studies – birds are caught and a small ring placed around a leg containing information identifying the individual bird and contact details for the ringer. If the bird is re-found that location and date can be sent to the ringer. Bird-ringing in Britain is performed only under licence from the BTO (British Trust for Ornithology) after a long apprenticeship with an experienced ringer. The size and weight of rings are chosen to prevent impacts on bird behaviour and survival.

Coloured rings are also used with letter/number codes which can be read without catching the birds, using binoculars or a camera. The picture is of a Mute swan showing a colour ring. Black-headed gulls are great for this kind of study as they often stand on fences and walls in urban environments giving a better chance of being re-sighted.

In our area, Black-headed gulls have been ringed in Otley, by the Waterbird colour-marking group. I learnt about the Otley birds through social media where @Calybites on Twitter/X reports on “their” gulls returning each autumn. In the spring, some have been reported from Sweden, Denmark and Finland where they probably breed – east-west journeys, rather than south-north migrations.

This technology is relatively cheap but isn’t a full itinerary. One Black-headed gull, ringed as a chick in the Yorkshire Dales in 1999 was re-sighted in Southport in 2010 and 2020. Where was it between those dates? Keep an eye out for colour rings and you could help fill gaps in our knowledge of bird migration journeys.