Instead of upgrading my Canon 100-400 f4-5.6 version I with the new version II, I purchased the new Sigma 150-600mm f/5-6.3 DG OS HSM Contemporary Lens which has received highly positive reviews .

Gear: Sigma 150-600 set to 600mm atop my Canon 1D Mark IV with Canon 1.4x III, hence a calculated 840mm, but with the 1.25x crop of the camera body, the equivalent focal length is 1050mm. All shots were taken hand-held or with a monopod tucked into my belt. The selected pictures were culled from ~1000 shots taken within a 2 hr period- this was a particularly lucky day with very active kites and the hawk.

White-tailed kite

Red-tailed hawk and 1 of the 4 kites in the area

A fight for territory, pass 1: the hawk eluding the kite which had dive-bombed the hawk

Hawk chasing one of the kites

Great view of the red-tailed hawk