I follow the Nature Conservancy on Facebook and enjoy the photos they post. I just saw that they posted their annual photo contest winners but was surprised to see the Grand Prize winning photo since, to me at least, it looks like a composite . I'm no expert and have a hard time drawing much of a conclusion from a pic that's 800 pixels on the long side so I thought I'd get the opinions from the more experienced photographers here on CiC.
The doubts I have are mostly on the depth of field in the pic. Both birds seem to be in focus but the blur of the not too distant background seems rather sudden in relation to the second bird. Could this be a combination of the effect of compression from a long lens, that makes the background seem closer, and maybe also the low resolution hiding the fact that the second bird isn't completely in focus? Besides that, I wasn't sure about the likelihood of catching those two birds flying together or what might be slight differences in the lighting on the two birds.
Looking at the other winners I would guess that this photo has to be a single photo and I'm sure the judges would know much better than me, I'm just hoping to get some other opinions and learn something about what I'm seeing, or not.
The other photos are excellent as well, I especially like 'Bear' by Jim James, Wow!