Yes Snafu, they will indeed committ kamkazi. And not just divers, but puddlers too-escpecially Mallards. the 2 things I have found best to minimize lost cripples is:
Using High Velocity steel shot loads, this means 1450+fps loads. They hit harder and penetrate deeper. Remember the pellet has to go through the feathers, meat, and breast plate/bone to get to the vidals to kill it.
The second is make sure they are close in and not beyond your effective range of your capabilities.
Granted a reg 1300 fps load is effective to 35 yds--but what about when the 2nd or third shot is over this range? Thus why I use HV. That or discipline yourself of no shooting over 35yds with the slower loads-but many guys can not do it and are tempted to take a long shot. And a big part of it too is that many do NOT gauge range accuratelty, often shots they think are at 35 yds are actually 45 yds shots based upon scientific survey ananalysis.
Also a great cripple load is #6 shot for the head shots. It is hard to find a 1.25 oz loads of it-but it makes for a good dense pattern to 40yds. It is ballistically effective to 42yds as I recall-but a strong wind will blow the pattern too often 3' sideways. So an alternative is #4 shot for cripple loads and it is much more easier to find it than a #6 shot heavy payload is. I keep and extra box of "cripple" loads in my hunting kit and always have 3 cripple load shells in my hunting coat pocket, just for is case I need them. Also, aim a hair below the head when shooting a cripple. Often the pellets rechioche (sp?) off the water, so aiming a little below will put more pellets at the haed for a better chance of hitting it.
BTW--I shot 13 times at one crippled Blue Bill, everytime I squeezed off it doove before the shot got there only to pop up 15 yds further away. All shots were within 40 yds. Yes I got him--that was one expensive bird.
Also often you will not see the body of the bird-only the top of the head swimming along-so look for it being small like 1/2 of a small egg and a wake - look for the head-not the body if you knock down a bird and it "disappears".
I hope these tips helps a few of the less experienced guys out there.