"Very cool moment you captured there. I've never seen Cranes and Ducks fly together like that.
My first impression is that the birds have sort of a cardboard cutout look to them which is most likely over sharpening. Either that or perhaps too much opening up of shadow detail as the undersides of the wings look as bright or brighter than the topsides which seems like unusual lighting on a blue sky day. Did you do a sky replacement or otherwise mask or select the birds vs the background? "
I would agree with this. Great moment, technically very good, but does not look "real". Looks like the ducks were "photoshoped" into the image. Less sharpening might help, less contrast and like Callie noted, maybe bringing down the blue in the sky might make the ducks look more like they belong there.
Unique image in any case.