[TN-Bird] Re: species apparently in decline (BBS data)

Perhaps the best answer to these questions can be found at the source of the 
BBS project. I have heard these very good questions debated in many different 
forums. The best stab at answering them, including explaining how biases and 
habitat changes are accounted for in the analysis, can be found at the BBS home 
page of the USGS. If you are interested, I recommend you taking a look at: 

http://www.mbr-pwrc.usgs.gov/bbs/bbs.html

Troy Ettel
Nashville

>>> "David F. Vogt" <dfv@xxxxxxxxxx> 03/30/03 02:43PM >>>



> -----Original Message-----
> From:    OLCOOT1@xxxxxxx [SMTP:OLCOOT1@xxxxxxx]
> Sent:    Sunday, March 30, 2003 7:20 AM
> To:    jwcoffey@xxxxxxxxxx; tn-bird@xxxxxxxxxxxxx
> Subject:    [TN-Bird] Re: species apparently in decline (BBS data)
> 
> Jeff,
> The BBS may not be the last word determining the state of bird population
> in North America and, it certainly does not comprehensively sample the
> entire North American Continent. But, I believe that it does sample a
> significant cross section and accurately reflects bird population trends.
> I agree that the change in habitat on a single route can change
> significantly over the years (when running a route in middle TN this June
> I noticed that I had described one stop as a scrubby field  but, this spot
> 18 years later is now what I would describe as oak hickory woods).
> However,  since thousands of routes are conducted across the continent,
> the over all results should reflect the changes of habitat North America.
> The fact that the study is a roadside study undoubtedly results in some
> bias but I believe it probably fairly accurately reflects the current
> population trends.  Results of studies pertaining to TV tower casualties
> collection and weather radar reflect similar population declines. 
> 
>  In a message dated 3/28/03 2:01:27 PM Central Standard Time, 
> jwcoffey@xxxxxxxxxx writes:
> 
> > North American species apparently in decline according to Breeding Bird
> > Survey (BBS) data.
> > 
> 
> I was hoping someone could answer to the following question. BBS are fixed
> 
> routes run over many years (The above report was just a 10 year period)
> how 
> do they adjust or justify the numbers when there is a tremendous
> generational 
> change in habitat along most routes that I know. Some formally rural
> routes 
> are now settled. Some agricultural routes which once sported wide fence
> rows 
> now are farmed to the fence lines. Generally, farm practices in regions 
> change, such as extensive flooded rice fields where there had been cotton
> or 
> soybeans. Tree farms where there had been mixed hardwoods. Once fallow
> fields 
> are grown up in trees. If the exact habitat is not present over these
> periods 
> then the exact birds surely are not present.
> 
> I do not deny a decline in many species but of those listed I have seen 
> habitat changes shift the concentrations from one location to another. 
> Therefore a species can increase or decrease on a route but the species 
> numbers stay the same in the area. If you are looking for Red-headed 
> Woodpeckers in an area where the prime older woods have been clear cut and
> it 
> is now new growth, you are not going to find them, but 2 miles away in 
> another woods that has matured or been selectively cut you will find
> plenty. 
> It's habitat, habitat, habitat. Just as others, I have seen marked
> increases 
> in some of the species listed in my area in the 20 plus years I've been 
> birding.
> 
> I'm sure they have a mechanism that adjusts for this habitat change but I 
> would like to know how it works.
> 
> Good Birding!!!
> 
> Jeff R. Wilson
> OL' COOT / TLBA
> Bartlett Tenn.
> 
> 
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