Missing Mammals?

 Animal population distributions can be assessed using iNaturalist.  The website is used by citizen scientists to report animal and plant observations.  Rare animals may not be mapped well, but my hypothesis is that large mammals are well mapped because humans tend to make note of them.  This may be less true for nocturnal animals, and it also depends on the presence of humans.

Raccoon observation from iNaturalist.

The map above of raccoons and the map below of coyote observations shows that both species are well-distributed across the U.S.  Clusters of observations are probably more likely due to sampling bias around large cities rather than actual differences in population density. 

Therefore, these maps can show overall distribution but may not be as useful for determining densities.

Coyote observations from iNaturalist.

The next map shows that moles do not occur in the central arid and mountainous part of the U.S.  It appears that these animals need mesic conditions and rich soil.

Mole (family) observations from iNaturalist.

In contrast, Pocket Gophers, a similar group of burrowing animals, are found throughout the arid West as well as along the Pacific coast and in Florida.

Pocket Gophers

But another burrowing mammal, the Prairie Dog, is restricted to the arid West:

Prairie Dogs

While the Prairie Dog distribution makes sense at the continental scale, zooming in reveals interesting patterns.  In northern AZ, Prairie Dogs are mainly restricted to the I-40 corridor, despite extensive grassland habitat in, for example, the Chino and Prescott valley area. The data for this zoomed-in view is much sparser than the national map and it is likely that there are many areas with missing observations. 

However, I am confident that any highly-visible Prairie Dog colonies in the Prescott area would have been photographed at some point.  Given the presence of suitable habitat surrounding occupied habitat in AZ, it may be that Prairie Dogs populations have been extirpated and fragmented across northern AZ.

Prairie Dog observations in northern AZ.

Each of the above species distributions can be related to environmental variables, but other mammal distributions are more complex.  Porcupines feed on the growing tips of conifer and deciduous trees, but apparently do not occur in much of the Midwest and southeastern parts of the U.S.  I'm not sure why this would be, as there is plenty of what looks like suitable habitat in these regions, and the presence of the species in the southwest and the northeast spans a large environmental gradient.

Porcupine distribution

Porcupine observations are quite scattered across much of the West, despite the fact that they are fairly visible in trees; birders looking for birds would be very likely to see them. There are large areas of suitable habitat in AZ, for example along the Verde river in Cottonwood.  I'm not sure why this species hasn't been observed anywhere on the Verde river.  Perhaps it has been extirpated from these areas.  Or, the two observations around Prescott may have been of dispersing animals and the population is only reproducing in the higher elevations around Flagstaff.

Porcupines in northern AZ.

Badgers also show a predominantly Western and great-plains distribution.  They need large areas of open space.

Badger distribution

However, in Northern AZ few animals have been observed.  This nocturnal burrowing animal may simply escape frequent detection, or it may be very infrequent on the landscape.  Supporting the idea that humans rarely encounter this animal, many of these observations are road kill.  Interestingly, badgers are found in AZ both in high-elevation mountain habitats and in low-elevation Sonoran desert habitat!

Badgers observations in AZ.

 Another animal with a strange distribution is the Opossum.  It seems to avoid most of the interior arid West, except for southern AZ.  The observations in Tucson would seem to be environmental outliers compared to the populations along the West coast and in the Eastern U.S.

Opossum distribution.  

Much can be learned by studying species distributions and noting where animals have been observed as well as where they have not.  Trying to explain the observed distributions raises many questions. The mysteries surrounding animal distributions are fertile ground for theorizing about animal behavior, history, and habitat needs.