WHAT IS A GOOD ABA AREA NATIVE MAMMAL LIST?
Brian W. Keelan
With the number of bird list totals published by the ABA, it's easy to get an idea of what constitues a good list, whether it be a year list, state list, ABA area list, or other. With no similar compilation of lists for mammals in the ABA area, it is much more difficult to become calibrated. So what I will do in this analysis is attempt to estimate what an expected mammal list would be for a birder who has traveled extensively throughout the ABA area, has reached an ABA total of around 700, and has paid very careful attention to mammals everywhere he or she went. This should give some idea what a good mammal list might be. I'll review the prognosis by order, giving the types of animals in the order, the total number of species in the ABA area, some comments, and finally, in square brackets, my assumed total for an observer like that described above.
Didelphimorphia: Marsupials. 1 sp. (Virvinia Opossum). Should be seen. 
Insectivora: Shrews and moles. 45 spp. Rarely seen, difficult to identify, but "Shrew sp." is reasonable to expect. 
Chiroptera: 47 spp. Bats. Encountered not infrequently but usually difficult to identify. A few species can be seen leaving known roosts (e.g., Mexican Free-tailed Bat) or can be identified on the wing (e.g., pipistrelles), or are sometimes found roosting during the day (e.g., Hoary Bat).  Note: if an observer were to become proficient at ultrasonic recording of echolocation calls, he or she could hope to identify 50% or more of the ABA area species. See Recording and Identifying Bat Echolocation Calls for more information on this topic.
Xenarthra: Armadillo. 1 sp. Should be seen. 
Lagomorpha: Rabbits, hares, and pikas. 20 spp. Often fairly easy to see and identify, except for some cottontails, which can be elusive and hard to distinguish. 
Rodentia except Sciuridae: Rodents except the squirrel family. 142 spp. Mostly nocturnal and difficult to identify, though driving roads after dark will often produce sightings that can be identified to genus, e.g., Kangaroo Rat sp., Woodrat sp., Deermouse sp., etc. A few of the larger species (American Beaver, Porcupine, and Muskrat) are not hard to see. 
Sciuridae: Squirrels, chipmunks, marmots, and prairie dogs. 67 spp. These are mostly diurnal and not too hard to find. Chipmunks can be challenging to identify, but in most areas only a few species occur, and with experience the majority can be identified confidently. Finding 50% of the species is a reasonable goal, though with research and targeted efforts, a much higher percentage (90%+) can be tracked down. 
Carnivora: Cats, dogs, weasels, pinnipeds, bears, skunks, raccoons, etc. 52 spp. A diverse order containing many highly desired species. It would be a good accomplishment to see 40% of the species. 
Cetacea: Whales, dolphins, and porpoises. 50 spp. Pelagic trips provide an ideal opportunity to see a selection of marine mammals, and leaders can help with identification challenges. A birder taking 20 pelagic trips from both southern and central to northern ports on both coasts might expect to encounter about 20% of the species. 
Sirenia: Manatee. 1 sp. Should be seen in Florida in winter, with a little research. 
Artiodactyla: Even-toed Ungulates (a. k. a. "hoofers"). 12 spp. Most species are reasonably easy to see in at least some national parks that a birder is likely to visit, even if primarily for purposes other than birding. The exception is Muskox, which is not conveniently reached (note: animals in Alaska are introduced). 
The total of the numbers in square brackets is exactly 100, which is not a rigged number -- that is just how it came out. One hundred native mammals in the ABA area is a fine total!