common or arctic

hi readers
over the past week or so i have seen many ducks on the canal. it starts with the pintail that is still there and there is a group of female mallards (about 8) which i find strange because if they are all in a line they fit halfway across the canal. there are also a lot of chicks aswell, there are small mallard chicks and there are some large coot chicks. unfortunately i haven't seen any moorhen chicks.
other news. i saw a fox run very quickly along the canal, but i didn't get a photo which is ashame.
now relating to the title of this post. today i saw what i thought to be a gull at first but it had a different shape and flew differently this is when i thought, could this be a tern. after it had darted round above the canal it dived down and came out with a fish in its mouth. then to my amazement, it swooped round and flew past me about 2 metres away. i got a good look then. i saw an orange beak and legs and a black head but only the top was black. i heard it very distinctively and when i checked my bird book i figured that it was either common or arctic tern and when i checked my bird songs cd i found that the sound i heard sounded much like an arctic tern.
if anyone in the area of wednesfield reads this and has seen this bird please comment or just comment on any recent findings you have made.