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Journal archives for April 2020

April 17, 2020

Limits of using geography for species identification

A recent observation highlighted the limitation of using geography to determine species on iNaturalist. If you take a close look at the photograph in https://www.inaturalist.org/observations/41662271 you may note that animal exhibits the characteristics of a mule deer rather than a white-tailed deer. However, the location makes it nearly inconceivable that it is a mule deer.

This is a conundrum that scientists often run into when using citizen science data. What can be inferred from a given observation, and how do you ensure the accuracy of it? It is generally more accurate to base identifications on field marks (physical characteristics) than location. This is the essence of birding and why people get so excited about rare birds showing up in odd locations. If people just ignored field marks and just considered geography, most of these rare birds would never be documented. But why do we ignore this principle with mammals?

In the deer example, as noted by @sambiology, the habitat in the photo doesn't fit north Dallas. This makes it most likely it is a mule deer and the location is simply wrong. But what happens when we know the location is accurate? Should we look at field marks or just consider geography? Take a look at 2 other observations and see what you think.

1) https://www.inaturalist.org/observations/18767407
In this case, we have what appears to be an American marten (with known location). But American martens are endangered in Wisconsin, and are unknown to occur in this area (before this observation). The field marks suggest American marten. The geography suggests it is actually a mink or fisher or some other mustelid or maybe a squirrel. Based on this observation, @lincolndurey extended the range map for American martens. But what if we had just labeled this as a squirrel and moved on without considering the field marks?

2) https://www.inaturalist.org/observations/20912284
Similar to #1, here we have what appears to be a fisher (with known location). But fishers are endangered in California and the population at the southern edge of the Coast Range is considered basically non-existent (before this observation). Specifically, the last fisher sighting this far south was made by Joseph Grinnel nearly a century ago. The field marks suggest this is a fisher. The geography suggests it is a mink or squirrel. Based on this observation, fisher researchers have extended the known range of fishers in the Coast Range of California. But what if we had just labeled this as a squirrel and moved on without considering the field marks?

Posted on April 17, 2020 16:32 by maxallen maxallen | 6 comments | Leave a comment


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