Yeah, the extreme cropping of the hawk image would pretty much render any image of it grainy.
The hummingbird image is slightly different. You'll get way, WAY more grain/noise at ISO 3200 than lower settings. The ISO doesn't really make the camera more sensitive to light; it just amps up the gain on the sensor.
And unless you're dealing with a low-light beast like a Sony a7s, high ISO in the the 3200 range just kills your dynamic range when processing images.