Three billion lost birds, and what else don’t I know?

Image: Blackpoll warbler (one of the declining species), © Simon Barrette CC BY-SA 3.0 via

You saw the headline (and maybe you read the study): three billion lost birds.  Three billion fewer birds in North America than there were in 1970.  It’s eye-catching, isn’t it?  There are (as is usually true) some reasons to interpret the result with nuance, but that isn’t my point today – Brian McGill has covered that with admirable thoroughness over on Dynamic Ecology. Instead, I’ll dig briefly into what the study told me about my own ignorance. Three billion is the change.  How many birds remain – and could I have answered that question before seeing the study?

The authors estimate that the three billion lost birds represent about 29% of 1970 abundances, so a quick calculation suggests about 7 billion birds in North America today.  That number in itself isn’t very interesting.  What is interesting is that I could not have guessed it even to plus or minus an order of magnitude.  In other words, I couldn’t have suggested an envelope containing the true number, even if I was allowed to make the envelope two orders of magnitude wide (a guess of 10 to 1000 billion, for example, would be a failure even though it builds in a huge range).  With respect to bird abundances, I wasn’t just a little unsure – I was astonishingly uniformed.

I’m not saying that as an ecologist, or as a citizen, I should have been better informed about this number.  I don’t think it’s a terribly important thing for me to know.  It’s just interesting that I couldn’t even guess to plus or minus an order of magnitude.  It seems like if I’m allowed to be that imprecise, I should be able to guess anything.

Could I?  Guess anything within plus or minus an order of magnitude?  That’s where my mind went.  I quickly decided that with that criterion, I could guess the human population of any country on Earth, the height of any mountain on Earth, the distance right now from me to any planet in the solar system, the speed record for any human conveyance and any animal, the number of words in any novel ever published, and a whole lot more things (all of which are arguably pretty trivial).  That’s even without looking anything up or writing anything down.  With access to paper and pencil and 30 seconds on the internet, I could add things like the volume in hogsheads of Lake Superior or the number of bricks in any building worldwide.  I’m not showing off; these feats don’t make me particularly smart.  They just reflect how low I’m setting the bar by claiming a good guess if I’m within plus or minus an order of magnitude.

So far, you could be forgiven for thinking everything in this post is ineffably trivial (well, except the original study).  But here’s a number that I can’t estimate to within plus or minus an order of magnitude – even if I had unlimited access to every library on Earth.  And it’s an important number.  With how many living species do we share our planet?

That’s right, I’m a professional biologist, and probably the most fundamental number in defining my own field is something I don’t know even plus or minus an order of magnitude!  And it gets worse: if you ask how many species have ever lived on Earth, I can’t guess even to within plus or minus two orders of magnitude.  This is a level of ignorance that’s really quite breathtaking.

But it’s not just my ignorance: no biologist knows these numbers.  Estimates for living insects alone range from 3 to 300 million.  Our estimates for fungi might be even more imprecise, and our estimates for bacteria definitely are.  There are periodic calls for megaprojects to document and describe all living species; the one that got the furthest was probably the “All Species Foundation”, an initiative in the early 2000s that had funding and momentum for a brief period before fizzling when the dot-com bubble burst.

What would it cost to figure out the number I’m after – to complete the job the All Species Foundation had in mind?  Estimates vary widely, but in my forthcoming book, Charles Darwin’s Barnacle and David Bowie’s Spider, I draw on some recent studies to guesstimate about $800 billion.*  It would take some time, of course, so let’s imagine a 20-year crash program at $40 billion per year.  $40 billion is less than half what the world spends on coffee, less than a quarter of what we spend shopping at Amazon, or less than 2.5% of global military spending.  In other words: a complete inventory of Earth’s biodiversity would be easily achievable, by a society that chose to achieve it.  So far, we have not made that choice.  As long as we’re talking about breathtaking levels of ignorance: how about our choice to spend $80 billion a year on coffee while refusing to spend half that to learn the most fundamental number in all of biology?

© Stephen Heard  October 1, 2019

*^I’m confident that this number is within plus or minus an order of magnitude of the true figure.  How fitting!  But the number we’d buy for the $800 billion would be much more precise.

3 thoughts on “Three billion lost birds, and what else don’t I know?

  1. Ken Hughes

    Have you heard of the Fermi problem? Which is “How many piano tuners are there in Chicago?” The idea is that the answer is an arbitrary bit of information, but if you appropriately multiply and divide rough estimates of numbers that are easier to guess (like Chicago’s population or the percentage of households with a piano), you can get much closer to a reasonable answer.
    Number of birds or number of species is certainly a harder answer to reach, but I’m sure this approach would help


    1. ScientistSeesSquirrel Post author

      Yes, and that’s how I’d get estimates for the things I mention being able to estimate. For bird numbers, I don’t have enough intuition to estimate the components. For global biodiversity, what’s astonishing is that nobody does!

      Liked by 1 person

  2. Anonymous

    I know I’m late to this post, and I imagine you already saw this, but this Nature piece on Thomas Crowther’s efforts to map different forms of life ties into this post nicely:

    These are daunting questions for sure. I feel hopeful that there are people being funded that are trying to answer these questions. Do you know of any other large scale efforts to determine global abundance like this?



Comment on this post:

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.