Shooting birds with depth

I downloaded an app called "DOF Master" awhile back thinking that this would be used entirely for landscape shots. I figured I would have it handy on my phone while setting up shots. So far, I have not used it as I planned. So I started thinking about depth of field (DOF) when I shoot birds, specifically multiple birds in a frame. Most of the time, I find that some birds lack focus because of my failure to adjust the DOF correctly and while everything else about the image works, that one issue kills it for me. For example, the first image below was shot with an aperture of f8.0 at 400mm focal length. My focus distance was probably less than 80 feet. According to the DOF Master, at 75 ft, the total DOF was 2.93 ft, which means there was less than 1.5 feet of focus behind and in front of the front bird, where I focused. The bird behind it looks to be about 1.5 ft away from it and when you examine the details on the birds, you can see that the second bird is slightly out of focus.

 Here's another one that did not make the grade, a classic flock of ibises coming in for landing. While I like many things about this image, lighting, background, positioning of the birds (and the fact they are all juveniles), the fact that I shot it at an aperture of f5.6 at 420mm killed it for me. With closer examination, the birds in flight are out of focus and at best guess I was about 100 feet away from them. With my settings, my DOF was less than 4 feet, and for sure, the incoming birds were not captured within that narrow range.

In the next image, the birds were much closer, probably 60 feet give or take 10. I shot it at f5.6 at 400mm. According to DOF Master, I had only 1.5 feet of DOF to work with. But, unlike the birds in the images above, these two birds are basically on the same plane of focus, so both are sharp.

Here's another image of multiple birds where one bird (the ibis) appears to be about 1 foot behind the black-necked stilt on the left, where I focused the lens. I was probably at least 80 feet away from the birds. I used an aperture of f8 with a focal length of 420mm. According to DOF Master, I had 3.5 feet of DOF, just enough to get all three birds in focused.

It isn't so much about the wading birds, but rather the nesting birds where DOF becomes such an important aspect of an image. Most of my images from the great white egret rookery include at least two birds in the frame. Last year, I was mesmerized by about 3 or 4 nests that all fell within a frame when I zoomed out to 250mm. The image below was shot at 400mm with an aperture of f5.6. I got away with the narrow DOF because I was about 120 ft away from the birds. I focused on the front parent and chick and according to DOF Master, I had about 3 feet of distance behind the front bird to work with. The second mother and chick focused in quite nicely as a result; but in retrospect, I would have preferred more DOF at f8 or f9.

The next image was at 300mm and f9.0. I was about 80 feet away and the DOF Master indicates that I had almost 8 feet of DOF. The last image was shot at 250mm, f9.0 and here I had over 11 feet of DOF. Both images had plenty of focus to go around to all the birds in the frame.

So with some thoughtful execution, the correct aperture setting will get all your birds in focus. Always consider three things, the distance between you and the subject (the shorter the distance, the lower the DOF), the lens focal length (the greater the length, the lower the DOF) and of course the aperture (the wider the aperture, the lower the DOF).