Common Loons typically arrive in my area some time around late March to early April. My first sighting this year occurred on April 14th. That day I spotted two loons but they were boat-shy and repeatedly submerged while I was still about 100 yards distant; too far for good photographs with any lens.
However my luck changed April 20th when I spotted this lone loon hanging out near the breast wall of the lake.
Stretching its leg
The loon remained calm as I approached to within less than 30 yards.
Loon with eyes underwater
Soon the loon ducked its head underwater and began searching for a morning meal. I have observed a number of fish-eating birds use this technique. The loon cruised for a short while until it located a school of shad.
Shad fleeing the feeding loon
I was able to track the loons underwater movements by the eruptions of shad fleeing on the surface.
Loon moments after surfacing from feeding
Repeatedly I tried to capture the loon as it surfaced but each time I was behind the curve. The narrow field of view of the 600mm made following the fast paced action difficult.
In previous years I used a Canon 100-400mm lens for all of my boat/waterfowl shooting however this spring I have been using the 600 F4 almost exclusively. The 600mm is nowhere nearly as handy as the little 100-400mm which can be shot handheld when light levels allow. The 600 is too heavy to support hand-held for long and I have resorted to setting the tripod on the front of the boat. With a gimbal head it works well tracking swimming birds as long as the water is reasonably calm, however I have found it very difficult to operate the boat and track flying birds simultaneously. Despite its drawbacks (weight & bulk) the superior range and sharpness of the 600 F4 IS is well worth the additional effort.