A very nice shot, there BobG.
If you think an hour is a long time, then my wife will correct you on that ;D
As for getting shots coming out of the water, reaction time is everything and there is no substitute for that! Well, there is if you buy these laser triggers and bait the water with a submerged bucket of fish...
My only tactic was when they were perched I took a guess at where they would dive and pre-focussed on that point so the camera focus time was reduced, so when they dived I could quickly focus on the point they hit the water. I also practiced like crazy on picking an object and seeing if I could put the camera to my eye and have the centre spot right on it.
What camera and lens are you using? When I got my 7D2 to replace the 7D I was hoping that case 5 may have helped (focus on things entering the focus area - in this case, emerging from the water) but that year our kingfishers went all shy and I hardly saw them, so there are potentially ways the gear can help.
I see you are using a 40D (so the AF area option is out for you) but also the 600mm f4L - that gives you a very narrow field of view so getting them in frame is harder and you may be better using a 400mm lens to make it easier to get them in the VF.
Your settings were f4.5, 1/500 and ISO 320.
With a 600mm lens your DOF is thin - I would try and get f8 as an absolute minimum and shutter speed over 1/1500.
The shot below was f8 at 560m (100-400 with 1.4tx), 1/750 at ISO 800 on the 7D MkI (not far removed from from the 40D in ISO capacity). You can see the splash is in focus but the tip of the beak isn't so f4.5 on 600mm will be even shallower DOF. At 1/750 the wings are a blur so focus is critical - the wing blur may not matter but these critters move fast and if your panning is not top-notch their movement across the frame will blur them.
Obviously if light is a premium then attempting with the setting you have is better than nothing but I would put ISO to at least 1600 with shutter speed at 1/1000 minimum and let the aperture fall where it may.
Oh...and enjoy the environment while waiting for the blighters to show up and do something!