During a stay in the national forest along the Mogollon Rim in Arizona (a.k.a. the southern edge of the Colorado plateau), I noticed this hummingbird repeatedly eating from the same prickly pear cactus throughout the day.  

I was able to take the below picture with the Nikon 200-400mm lens with the 1.4x teleconverter attached.  It was a challenging shot since hummingbirds are very fast and rarely hang still for more than a split second.  I needed a fast shutter speed to freeze the hummingbird's action plus a small aperture to provide the needed depth of field.  The depth of field is very narrow at these focal lengths (barely an inch).  Pushing up the ISO was my only option and I'm happy with how the Nikon D800 performed at high ISO (very little noise).

The below picture is my favorite of the ones I was able to take that day: it includes the hummingbird and the food it's there to eat.