In the 1990s, it was estimated that the Cooper's hawks may number well into six figures due to their regular distribution over 8 million square kilometers. Today, the Cooper's hawk is thought to number around 800,000 in the United States and Canada. These estimates were gained cross-referencing the number of hectares per active nest, which was in the range of in the western states and in the Midwestern and eastern states, as well as data from Christmas Bird Counts and migration counts. Evidence from long-time migration counts at Bake Oven Knob show slight peaks at intervals of 3 to 4 years, however no dramatic declines have been detected since the 1980s. Following their historic decline, Breeding Bird Surveys have tracked strong increases of the breeding population (upward trends from 1.2% in California to 4.4% in Pennsylvania) in six states, with a 2.2% increase overall, and similar trends in multiple other states. In many states (Arizona, California, Florida, Missouri, New Mexico and North Dakota) the numbers are probably similar or greater to those prior to 1945. It is thought that the population of Cooper's hawks in Wisconsin is nearly saturated relative to the landmass of the state, after a rough 25-fold increase since the late 1970s. Based largely on data from well-known populations such as Tucson and Milwaukee, some authors opine that the Cooper's hawk may be the most common raptor in American urban areas today, although surely other common raptorial birds such as red-tailed hawks, American kestrels and turkey vultures (Cathartes aura) may easily rival them in this regard.