I just returned from a walk to downtown Boise for a few errands. I planned my route to pass by the building housing the Peregrine Falcon Nest (webcam). A few blocks before I got there I saw one of the Peregrines flying overhead. I assume it to be the female due to its apparent larger size, but I could be wrong. I didn't have access to the web cam to see which one was still on the nest! Anyway, the falcon was causing quite a stir in the local bird community as you might expect from such an efficient predator.
In watching her behavior, I noticed a few significant points. First, she was clearly on a mission. This has always impressed me about adult predators. The deterministic focus that comes from having to catch your own food to survive. The second thing I noticed is that she was focused on a pair of Canada Geese, but did not appear to be making any move to take one of them. I would have been surprised if she had due to their much larger size. She did fly low over the pair while they were on the edge of a three story building. This caused them to squawk loudly and fly to the next building. She circled around and flew low over them again, causing them to move on to a third building. She repeated the process again, but never made any specific move toward the geese.
I have a few hypotheses regarding what she was up to. The first is that she could have just been testing them. This is common for predators to regularly test their prey. The second, and more likely in my mind, is that she was trying to co-opt the geese in her hunt. By forcing the geese to fly and squawk then they become the center of attention for other birds. If any other prey birds focus on the geese, the Peregrine could take advantage of the distraction to grab the prey. Just a theory, but it definitely seemed like that is what was happening to me.