Winter for me means bird photography. This may sound odd given that I live in Minnesota, but this time of year is great time to find birds up here in the north land. Why is this? There are a lot of reasons, some of which are:
limited access to open water
arctic bird migration
lack of foliage
A great place to try and capture birds in flight is around open water. In Minnesota, this means eagles, swans, geese, and ducks. We also have migration periods in October and November where sand hill cranes and white pelicans move through the area. One thing that you learn pretty quickly is that the bigger the bird, the slower the bird.
Let's begin with a discussion around equipment. For birds in flight, a long telephoto lens is an absolute necessity. Fortunately, there are a number of very good long telephoto lenses sold by Tamron, Sigma, and Nikon that are "relatively" inexpensive. I have used both the Tamron 150-600, and the Nikon 200-500. Both lenses provide great results. Depending upon the lens you are using, and basic arm strength, you may also want to use either a tripod or monopod to provide additional stability.
For camera settings, the most important setting is shutter speed. Sharpness can be a big challenge because, both the subject and the photographer are moving. I have found that a shutter speed of at least 1/1250 is needed. Most of the time, I try to have my shutter speed set at 1/2000 or faster. This means that we need to make some adjustments for aperture and ISO. My preference is to try and find the smallest ISO value that I can get away with using. The secret is to find an ISO setting that allows you to slightly overexpose the shot when shooting with the aperture wide open. I often find that when shooting in the early morning or late afternoon, an ISO between 800 and 2000 is typically required. For aperture, I can be anywhere between wide open and f/8.
Finally, it comes down to focusing. With wildlife photography, we are taught to focus on the eye. This does not work as well for birds in flight. The reason for this is that the head tends to be small and with all the movement, it is too hard for the camera's autofocus to lock on. My preferred approach is to try and focus on the body of the bird. I have my camera in continuous focus mode, and I use back button focus. I then pan with the bird and shoot a burst of 5 shots.
The reason for the burst is wing position. Some birds look better with wings in a specific position. Most of the time, I prefer wings down since most of the wing detail tends to be on the top of the wing. The burst will give you a selection of wings up and down to choose from.