Wow nice why you choose iso 1250 if may i ask just to improve my photos
Obviously I didn't take the picture but it looks to me like iso 1250 was selected in order to ensure a fast enough shutter speed to freeze any small movements the bird might make and to help to avoid blur from camera shake. These are key to getting a sharp image. The lens was already wide open at f/6.3 so there was no way to increase the shutter speed by opening the aperture more.
If there was more light available the iso could be reduced to get a cleaner image with less grain and noise, whilst maintaining a fast shutter. As it is it looks like the D7200 handled the noise well at that iso.