Mapping squirrel color morphs - September 2019


The SquirrelMapper project on Zooniverse started in July 2019. We’re delighted to see that more than 1000 people have contributed to classifying the coat color of eastern gray squirrels in just two months. Over at iNaturalist we’ve had over 15,000 contributors of squirrel photos and nearly 4000 participants help identify the squirrels observed in those photos. Thanks to all the citizen scientists for making this project a success.

This is a brief update on patterns we’ve observed with the data collected up to September 12, 2019. At that point 13,199 squirrel photos have been classified for coat color by at least 10 people. The bulk of the observations have been from the eastern U.S. and southeastern Canada where gray squirrels are native, but we’ve also received observations from places where gray squirrels have been introduced, including the U.K., Ireland, Italy, South Africa, and a handful of cities in western North America. Here’s a map of the worldwide distribution of squirrels classified here on Zooniverse:

world_obs.png

world_obs.png

Not all of the 13,199 make it to the data analysis stage. Some photos don’t actually include a physical squirrel (e.g., tracks in snow), and sometimes there’s not agreement among observers on how many squirrels are present or the coat color of those squirrels. The patterns shown below are based on 10,629 photos of a single physical squirrel where there was at least 80% agreement among observers on on the squirrel’s coat color.

The map below shows the color morphs are squirrels in the United States and Canada (red dots = black morph, gray dots = gray morph). Places where the shade of the dots are darkest represent places with the most observations of each squirrel morph. Black squirrels are most common in the northern part of the eastern gray squirrel’s native range, and they tend to cluster around cities, particularly Toronto, Detroit, and Cleveland, as well as cities along the U.S. east coast. We know black squirrels have a thermal advantage over grays in the winter, but they can be quite prevalent even in places with moderate temperatures, such as the introduced populations near Vancouver, Can and the San Francisco Bay Area in California.

NA_points.png

NA_points.png

Here’s another map showing the distribution of color morphs in North America, this time with the data summarized as the percentage of black squirrels in a standard grid. This map shows largely the same pattern but should be interpreted with caution because some grid cells have very few squirrel observations.

NA_chloropeth.png

NA_chloropeth.png

Here’s the situation in Europe, where the vast majority of squirrel observations have been of the gray morph:

Eurmap.png

Eurmap.png

That’s it for now. Many thanks to all the citizen scientists who are contributing to this project!