# Re: [nysbirds-l] Fwd: News Alert: North America has lost 29% of its birds since 1970, study finds. Experts blame habitat loss, pesticides, light pollution and cats.

```Hi Gus,

I really think it's just an artifact of the way the figure was made, and not
something with a complicated biological explanation. To me it looks like a
simple function that illustrates the entire estimated decline from 10 to 7, as
though the current population size was the end point. In other words, the
graphic looks like the exponential loss of 3 billion birds, starting with all
of the 3 billion birds that used to exist, to the zero of those birds that
remain today.```
```
Shai
_______________________________________
From: Gus Keri [gusk...@zoho.com]
Sent: Sunday, September 22, 2019 12:35 PM
To: Shaibal Mitra
Cc: NYSBIRDS (NYSBIRDS-L@cornell.edu)
Subject: RE: [nysbirds-l] Fwd: News Alert: North America has lost 29% of its
birds since 1970, study finds. Experts blame habitat loss, pesticides, light
pollution and cats.

Hi Shaibal,

I took into consideration the possibility of exponential  decline but it didn't
look like that.
If you calculate the decline in relation to the absolute number of birds at the
beginning of each decade, the difference is more remarkable.
Here is the percentage of decline for each decade alone:
By the end of the 70s: 12%
By the end of the 80s: 9%
By the end of the 90s: 7%
BY the end if the 2000s: 4%
By now: 1-2%

I don't know if birds are finding a way to adjust with all the environmental
changes that are taking place, or there are other factors involved.

Sent using Zoho Mail

---- On Sun, 22 Sep 2019 12:01:35 -0400 Shaibal Mitra
<shaibal.mi...@csi.cuny.edu> wrote ----
> Hi Gus and all,
>
> The curve in the link has the shape characteristic of exponential decline at
> a constant rate. It has the properties you describe, with the amount of
> absolute loss diminishing in the recent years, because the population itself
> is getting smaller all the time. I suspect that this graphic is not to be
> taken literally but instead is a simple, fitted function meant to express
> the overall rate of loss that was estimated over these decades.
>
> Best,
> Shai
> ________________________________________
> From: bounce-123944861-3714...@list.cornell.edu
> [bounce-123944861-3714...@list.cornell.edu] on behalf of Gus Keri
> [gusk...@zoho.com]
> Sent: Saturday, September 21, 2019 6:57 PM
> To: Anne Swaim
> Subject: Re: [nysbirds-l] Fwd: News Alert: North America has lost 29% of its
> birds since 1970, study finds. Experts blame habitat loss, pesticides, light
> pollution and cats.
>
>
> The shape of the curve on the graphic in the above article is very
> intriguing to me. It starts with a steep decline in the first couple of
> decades and plateaued toward the last few years.
> The curve suggests that more than 75% of birds losses happened in the first
> 25 years (betwween 1970 and 1995) and less than 25% of the losses took place
> in the last 25 years(from 1995 to present).
> The fact that habitat loss, climate changes and other adverse environmental
> changes are worse in the last 25 years compared to the previous period
> suggests other factors are at play to slow down the decline of the total
> population.
> Does anyone have any explanation for this contradiction?
>
> Sent using Zoho Mail
>
>
>  ---- On Fri, 20 Sep 2019 07:18:43 -0400 Anne Swaim <annesw...@gmail.com>
> wrote ----
> Lab's website
>  also linked from accompanying Living Birds article
>  >
>  > Anne SwaimSaw Mill River Audubonwww.sawmillriveraudubon.org
>  >
>  >
>  >
>  > On Thu, Sep 19, 2019 at 9:29 PM Anne Swaim <annesw...@gmail.com> wrote:
>  > Further on this topic: someone just passed along a PDF of full text of
> the study.
>  > Reply off list, if a copy would be of interest.
>  > Anne SwaimSaw Mill River Audubonwww.sawmillriveraudubon.org
>  >
>  >
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