Cumulative eBird Species Over Time

eBird

If you look at the bottom of the main eBird page, you’ll see that the total number of species reported world-wide, for all time, is 10,420. If you click on that number, you’ll get a list, just as you would if you were looking at the list of recently seen birds in your county or favorite hot-spot. The results are listed from most recently seen in reverse-chronological order.

I’ve been looking at that list for the past week or so, putting it into a spreadsheet and playing with the numbers. Specifically, I pulled the data on April 29th and on May 6, both Mondays. With the latter date coming after the “Big Day” weekend, it was expected that the rate at which species are picked up would be different. The plot is below:

csp
Cumulative number of species versus time; going left to right is going back in time. The leftmost point on the blue curve is for May 5,while for the orange it is April 28. Each point is one day. The Big Day Bump is evident.

I plotted the cumulative number of species recorded on eBird as a function of time (going backwards) in the above figure. Starting with the orange curve, which is for data pulled on April 29th, one can see that on April 28 (corresponding to the leftmost point), just under 1,000 species were reported. During the previous three days, the total was about 4,600. For the blue curve, where Big Day (and spring migration and improving weather, of course) played a role, we can see that about 6,800 species were recorded over three days.

Beyond that, the lines merge, as they must, and by the time we go back to 0.1 years, or just over five weeks, there is no significant difference.

Note that none of the “sensitive” species on eBird enter into this, since they not only have information about locations redacted, but also about the dates of the most recent sightings. There are 133 of these species; just under 1.3%, so the impact on the chart would be difficult to perceive.

The next interesting bit is that about 9,900 species have been recorded in the last 365 days. To get to an even 10,000, you need to go back 568 days, about a year and a half.  Go back five years to get to 10,164 species. Ten years and get to 10,204. But to get to 10,287, which is the total number of species in eBird excluding the sensitive species? You’ll need to go back to the earliest records they keep – 169 years old – for a Cuban Macaw from 1850.

The Cuban Macaw is long extinct, as are many other birds that make up the eBird 10,420 value. How many? I count at least 30 species, the most recent being Atitlan Grebe Podilymbus gigas, last reported in 1986. Sadly there are likely more. Assuming the 133 sensitive species are still doable (doubtful, with the Spix’s Macaw, for example, recently declared extinct), that leaves 10,390 as a more accurate estimate of bird species recognized by the eBird/Clements taxonomy that one could in principle, find.

Getting to half of the total species possible means 5,195… my goal is to get to this value, plus 1% more, just as a buffer – a 1% error rate in ID seems reasonable. That gets one to 5,247. Rounding up, this makes 5,250, my life list goal.

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