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Comment by abeppu | Hacker News Reader

Actually, is that really what the article said?

> Experts believe that habitat loss due to agricultural development and intensification is most likely the driving factor.

But I don't think the numbers in the article make sense together.

> wild bird populations in the continental U.S. and Canada have declined by 29 percent—or a total net loss of around three billion birds—since 1970.

> between 365 million and one billion birds die each year across the U.S. as a result of window strikes.)

> pet felines kill some 2.6 billion birds annually in the U.S. alone.

So ... the total decline over 50 years (~3B) is approximately the same as the annual deaths from cats and windows at somewhere between a quarter and a third of all birds? I think this is one of those cases where uncritically accepting estimates from independent sources who used different methods produces an incoherent picture.

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The article and numbers are right, it’s just not clearly worded.

I had this same question a couple years back when I read this stat, so I messaged the Cornell Lab Ornithology and one of their reps explained how these numbers make sense.

“We start with a population of breeding adult birds at the beginning of the year. They breed, and multiply, and then the population is "spent" throughout the year on deaths such as window strikes, pesticide poisoning, and cat kills. If the population could keep up with these deaths, we would see a net loss of zero. Unfortunately, instead, we are seeing less and less breeding adult birds at the beginning of each year.

So when we say "we've lost 2.9 Billion birds," what we really mean is, "We've seen a net loss of 2.9 billion breeding adult birds since the 1970's." Back in the 1970's, the breeding season started with about 13 billion adult birds. This year, we had about 10 billion. Throughout the year, they multiply to about 40 billion before they die back. Of that 40 billion, cats kill 2.5 billion.”

I think the honest answer is that we just don't have nearly as much surety around these numbers as you might expect.

I went looking for data on actual bird populations, and I get wildly different estimates.

The 3 billion number comes from the following source (as far as I can tell):

" Critical data were contributed by citizen-science participants in the Audubon Christmas Bird Count, North American Breeding Bird Survey, and other bird-monitoring initiatives. The Partners in Flight Avian Conservation Assessment Database was a critical source for the data. " - https://www.birds.cornell.edu/home/bring-birds-back/

Nat Geo quotes

" New research estimates there are between 50 billion and 430 billion birds on Earth. " - https://www.nationalgeographic.com/animals/article/how-many-...

A lot of articles seem to quote the "at least 50 billion" line, probably based on the above numbers.

Basically - I'd say we have no idea how many birds there really are. Take ALL numbers involved as wild guesses.

Counting population based on deaths alone isn't accurate

If the ecosystem is healthy, a dozen birds dying will make way for a dozen more to replace them

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