I recently found this savannah sparrow out in the open, pecking away at the ground for food. These sparrows are not as common in my area as the prolific white and golden-crowned sparrows. Savannah sparrows actually derive their name from Savannah, Georgia, where they were first classified.
That day, there were dark storm clouds in the sky and the light was very low. Only after taking several shots of this sparrow did I realize that I was still using ISO 400 (my typical starting point for bird photography), which lowered my shutter speed to only 1/125 sec. With an 800 mm lens, that is a bit too slow for comfort (even with a sturdy tripod). Anything slower than 1/250 sec introduces a real risk of camera shake, leading to a blurry photo. It is a true testament to Canon’s 4-stop lens image stabilization that I was able to pull these shots off, and with remarkable sharpness. If I had been paying better attention, I would have bumped my ISO to 800 (even though this would lead to more digital noise in the resulting photo), and thus halved my shutter speed.