Richard, I like the unusual background (no sand!) and the way the gull stands out against it. Since its legs are almost invisible it looks like it is floating, which I'm not so sure is good, makes it look a bit "artificial" to me. But I like the idea, if you could just get some legs in there.
Whites look pretty good. Good eye contact. Consider using a lower F stop then blur BG and FG which would render it less distracting. Light appears to coming from the left which puts the breast in shadow and thus noise on the chest. Some NR would help. Interesting to see it in the grass.
Hi Richard - F11 is overkill here - opening up would have blurred the BG more - making the Gull pop out from the BG a bit.
Would run some NR on the background - appears to be a black line along the back of the bird - possibly from over sharpening.
As with any black and white bird - soft light is the key.
Keep em coming :)