Cutting off legs and feet

Was it OK for me to crop of the bottom portion of the legs of this impala in South Africa?  In this case, I would argue that it was fine.  I wanted to capture the interaction between the red billed oxpecker and the impala, and had I included all of the legs I wouldn't have filled the frame with the important part of the picture. The bird would have been too small in the frame, and therefore too insignificant. It would have been wrong to cut off just the feet, however.  My feeling about this is that you have to crop decidedly, like I did here, or else it will look like a mistake.  The only thing I find a bit distracting is the tail of another animal in the upper right corner, but beside that, I like this a lot.  Oxpeckers eat ticks and other annoying insects off many of the animals in Africa, so it's a symbiotic relationship in which everyone benefits.  I thought this little nudge on the part of the impala was a 'thank you' to the bird for helping to keep him healthy.  The sunset lighting was beautiful, although I do wish that the shadow on the tip of the impala's nose wasn't there.