eBird Species Cartogram for the United States

The previous post presented a cartogram for global eBird data by county. Here, we do the same for the States (and Washington D.C.). It is worth noting what the starting conditions are; that is, what base map will be used to generate the cartogram. I am using the WGS84 geographic coordinate system/projection, shown here without any morphing:

Base map image from Natural Earth

A cartogram of the same map based on eBird species counts by states was produced using the QGIS cartogram plugin and is shown in the following figure. The colors of the states correspond to the number of lists submitted, with darker colors representing more lists.

Cartogram of total eBird species counts. Colors indicate number of lists submitted.

What jumps out is the large size of the New England states, an increase in the area of Florida, and a reduction to Texas. The loss in area for Texas leaves California slightly larger, reflecting its status as our leading state for species diversity.

Speaking of California, it is also the home to the best counties in the US for bird variety. There are nine counties in the state with higher species totals than any other county in the rest of the US:

  1. San Diego, 543
  2. Los Angeles, 540*
  3. Santa Barbara, 500
  4. Marin, 499
  5. Monterey, 495
  6. Orange, 483
  7. Humboldt, 474
  8. Ventura, 473
  9. San Francisco, 472
  10. Cochise (Arizona), 464

This seems counter-intuitive, at least to someone living far enough to the east; you would think that none of the many eastern warblers, south Texas or south Florida specialties would contribute to these high numbers. (A reader noted in the comments section that a number of eastern birds have been seen in these counties. A more detailed analysis is in order…)

Future posts will look into the county data more closely.

*I never would have thought that one could live in our second largest city and have access to more avian diversity than what is found in 46 other states, without leaving the county! And the 5th best county alone, Monterey, has more bird species than 40 entire states: Colorado, the 10th higher state, has 496, with number 11 New York at 484.

2 responses to “eBird Species Cartogram for the United States”

  1. Many eastern warblers do show up (as rarities) in those California counties and boost the species totals. For example, San Diego county has such eastern warblers such as the Black-throated Blue, Prothonotary, Hooded, and Kentucky and on the list (and those just from a quick glance at the list just from fall 2017).


  2. Thanks for the comment, Gregg. You’re right. What I’d like to do is determine the species counts by counties excluding rarities and the occasional oddball. Perhaps a threshold of 1.00% of lists would help eliminate these outliers.


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