A black egg-shaped UFO over river Tay, Scotland

On July 28, 2017, a couple was visiting the river Tay in Scotland. Over the water, he caught a photo of a weird UFO flying in the sky. This object can be described as a black egg. What is it?

Witness statement:

On July 28, 2017 I used to be at the seashore with household and we noticed dolphins in the river Tay. My girlfriend from Bulgaria does not consider that we’ve got dolphins in the river in Scotland so I attempted to snap some pictures of them with my Sony Xperia x 23mp camera. I took a number of photos whereas focusing on the water and after I appeared again to see if I had caught any dolphins rising, considered one of the pictures in the center of the set taken had a wierd brown egg formed object in the sky.