Gulls in Hereford

A lovely three night stay in Hereford.  On our first day, walking around the city, we were confronted by the noise and sight of gulls.

What are gulls doing in Hereford  so far from the sea?  Someone told me that there are now "land gulls" or "urban gulls", but I had never heard of this before.  They look grand, but the noise!