Additional images can be viewed here.
Photographing birds is an exercise of opportunism. I always carry a relatively long zoom lens but don't often find the necessary conditions to photograph birds, especially flying birds. Egrets and pelicans are generally the easiest to photograph as they fly relatively slowly without a lot of rapid changes in direction. Ducks are quite the opposite; they are fast and move quickly. Their rapid moving wings fake out the auto focus on even the best DSLRs making it extremely difficult to capture the dynamics of their flight.
I was recently visiting Safari Park in northern San Diego County and noticed ducks continuously flying from the flamingo pond at the entrance to a small lower pond. The big pond had been emptied for cleaning forcing the normal inhabitants into the smaller pond. The crowded conditions and back lighting made for a prime opportunity to photograph these often difficult to capture flying birds.
I had dozens of opportunity to capture different ducks in flight but it took a little while to warm up. These guys move fast and following them in flight takes a little practice. In the case of the image above, there were extreme lighting conditions from sun light, to back light, to shade. I originally began with a setting of F8 and ISO 800. On reviewing the images, the resulting shutter speed was simply too slow. I increased the ISO to 1600 and this was still a little too slow. I finally increased the ISO to 3200 and reduced the F stop to 5.6. This resulted in a shutter speed of about 1/1000 which finally resulted in stopping the birds wings to an acceptably sharp level.
The above image shot with a 70-400 F4.0- F5.6 zoom lens on a 16MP DSLR hand held.