There are three species of owl in the Gainsborough area.
A walk along the riverside at Gainsborough or Morton as dusk falls will sometimes produce a hunting Barn Owl. I have occasionally seen a Barn Owl on Field Lane near Morton. There was one on the Riverside by Roses Sports Field on Apr 11th 2018, and another (perhaps the same one) was flying around the woodyard on the opposite side of the river on Apr 20th 2018.
Barn Owl (pictures from Wikipedia)
There is a Tawny Owl that roosts in Mercers Wood. I have sometimes heard it hooting at night-time, and occasionally in the day when it has been disturbed by other birds. I have never managed to see it despite several attempts, but I have seen Tawny Owls at Morton.
Tawny Owl (picture from Wikipedia)
I have occasionally seen a Little Owl along the riverside, usually away from the town. There was a Little Owl on Walkerith Road, Morton on May 18th 2013, and another was heard calling from near Trentside School in Morton on May 28th 2018.
There were two calling to each other in Mercers Wood on May 30th 2018.
A Little Owl was being mobbed and chased away by several chaffinches at Jubilee Farm on Walkerith Road on Jun 24th 2018.
Little Owl (picture from Wikipedia)
I have never seen a Short-eared Owl in the Gainsborough area, although I have seen them in the Retford area. I once saw one at Stow some years ago, and the warden at Beckingham Marsh has occasionally reported one there.
Short-eared Owl (picture from Wikipedia)