This is an amazing study into the mysteries of bird language that investigate how chickadees communicate about a wide range of predators:http://students.washington.edu/ctemple2/chickadee.html
If you want to view the study in more depth, check out this link:
It is amazing to get such clear scientific information on how the vocalizations of black-capped chickadees relate directly to the types of predators that are around and how much of a threat they pose!
It appears the the number of "dee's" added after the more commonly used "chick-a-dee-dee-dee" call relates to the level of danger a predator poses to the flock and therefore points to the kind of predator that is likely around. The second link has a graph that includes 2 mammalian ground predators: ferret and house cat.