I have always struggled with capturing images of Birds in Flight (BIF). My go-to birding lens is the Nikon 600mm f/4 and for mere mortals like me, that is one heavy piece of glass – but an exceptional one nevertheless. And I find it quite impossible to reasonably hand-hold this lens long enough to try and get any decent flight shots.
I now have a second kit – with the super manoeuvrable and ultra-light Nikon 300f/4 PF lens. And it has now become a habit to carry both these combinations with me on every trip and use the 300f/4 for any BIF opportunities.
Even so, BIF poses quite a lot of challenges. The biggest of them is getting the hang of tracking the subject in flight and ensuring that it is composed just exactly so. Invariably, the speed of the bird and that of the camera tracking it go out of sync with each other and you end up with either the subject trailing off the frame (when you are tracking the subject too fast) or it has moved ahead and out of the frame (when you are tracking the subject too slow).
Selection of the right AF mode is another important consideration for shooting in situations like this. You will have to choose AF-C (in Nikon or the AI-Servo in Canon) to ensure that the camera will continuously keep acquiring focus as the subject is moving and the camera is tracking its movements. That alone is not enough though. If you are working with a smaller set of AF points than available, as I usually do, then there is a chance that the AF point strays from the subject as you are tracking it. This would cause the camera to acquire focus of a different part of the frame, say the background, and you would not have messed up the image. With the GRP (grouping) functionality now available in the D500, it is now a much easier task to keep the subject in focus while tracking.
The only way to get this right though is to practice at every available opportunity.
I got that at Bharatpur a few weeks back with this Bar-headed Goose. We were in a boat and came across a flock of these on the edge of the water. We waited for one of them to take off and that was the opportunity. Of course, being in a boat makes it quite tricky for such pictures as even a gentle rocking of the boat would throw compositions off kilter and I should thank my colleagues for being very stable and making measured movements.