
Three billion North American birds have vanished since 1970 - elorant
https://www.sciencemag.org/news/2019/09/three-billion-north-american-birds-have-vanished-1970-surveys-show
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ColinWright
Discussed extensively last week:

[https://news.ycombinator.com/item?id=21019995](https://news.ycombinator.com/item?id=21019995)

[https://news.ycombinator.com/item?id=21018916](https://news.ycombinator.com/item?id=21018916)

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elorant
Oops, sorry I missed it.

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coldtea
> _Since the 1970s, the continent has lost 3 billion birds, nearly 30% of the
> total, and even common birds such as sparrows and blackbirds are in decline,
> U.S. and Canadian researchers report this week online in Science_

So, at 1970s we had 9 billion birds, and we know have 6 billion birds?

I've seen articles that say: "Cats that live in the wild or indoor pets
allowed to roam outdoors kill from 1.4 billion to as many as 3.7 billion birds
in the continental U.S. each year, says a new study that escalates a decades-
old debate over the feline threat to native animals".

Compared to that, a drop of 3 billion birds "since the 70s" seem a tiny
number, no?

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Arnt
That doesn't follow.

Birds are generally prey and have a typical prey strategy; they lay lots of
eggs and expect few chicks to reach adulthood, while the large majority become
food for someone. Sparrows lay about four eggs per year and become >10 years
old, for example.

You should expect lots of sparrows to be eaten. Otherwise, the number of
sparrows would grow by >100% per year. What this study says is that the number
of chicks to reach adulthood is below two per hen, sustained for 50 years.

