If you used flash, you would have a bit more light on the shady side and some catch light in the eyes. The risk with flash on a raptor is that there light colored retna will reflect back at you which is very hard to fix so keep the power down.
I agree with Steve, you are better off with an SB910 as it has overheat protection. I melted a SB800 firing it too frequently.
Here's my first day out with Tamron 150-600mm.
It was early morning, still some fog, made kite's images soft even after sharpening applied. I liked the warm morning glow on Kite's belly.
I find this lens works great with good light, at close distance and when the object is stationary. Moving targets or distant objects are a little hard for me to get sharp images, operator error. I wouldn't compare this to Nikon 500mm/4 VR I sold, but I paid way below what I sold Nikon 500. If you've got great long lens technic, you'll be very happy, IMO.
