The linked blog post has some photos of a red-tailed hawk trying to catch squirrels in an urban park. Bob Arihoob notes that two hours of effort didn’t get the RTH anything.
There’s two comments to go with that. First, a lot of juvenile RTHs (as the barred tail on the one in the photos leads me to believe this one is) die in their first winter. If I recall correctly, the figure generally bandied about is about 70% mortality. An inept juvenile may be entertaining, but I can assure you that the issue is deadly serious for the bird. Squirrels are tough prey, fast, thick-skinned, and fully capable of biting off an RTH toe if the bird bungles the grab. Rusty, our 15-year-old very well-experienced Harris’s hawk will only bind to a squirrel if she is sure that she can get the squirrel’s head under control.
Second, the general poor ratio on prey capture attempts and successful catches for raptors like RTHs is what makes falconry possible. As one falconer put it, an RTH makes 20 attempts and catches once, where an osprey makes 20 attempts and fails to catch once. It is easy for a falconer to improve an RTH’s food acquisition ratio and convince it that hanging around the falconer is a good thing. It is generally considered very difficult to impossible for a falconer to successfully train and fly an osprey (harking back to the unregulated days pre-1918 when such could be considered); an osprey doesn’t need the falconer for anything.