Is it possible to disaggregate the data to see if the variations over time 
occurred across the board or were attributable to some places more than 

Willem van Vliet--

On Friday, April 13, 2018 at 12:52:32 PM UTC-6, wrote:
> Hi all,
> First off, hi! I'm brand new to this list. As dumb luck would have it, the 
> first post I ever received was yesterday from Diana Beatty. She had the 
> wonderful idea to do a linear regression on Christmas Bird Count (CBC) data 
> from Colorado Springs to see if there has been a decline in House Sparrow 
> population size since 1950. Due to my burgeoning interest in House Sparrows 
> as a graduate student, I asked her if she had any more details. In 
> response, she sent the raw data for me to have a look at. A big thanks to 
> her for sending that along!
> Diana's analysis was of course correct: that is, that when looking from 
> 1950-2017, there has been no overall trend toward decline. However, my eyes 
> wouldn't stop perceiving little peaks and dips in the cloud of data points. 
> So I split the data up and found that there have been 3 cycles of 
> statistically significant growth and decline since 1950. We're currently in 
> the middle of a decline that began in 2001.
> It's no surprise that there have been fluctuations in the 67 years of CBC 
> data that we have. All wild populations fluctuate. The interesting part is 
> telling a story as to why they fluctuate. Often, growth and decline cycles 
> have something to do with climatic patterns, possibly interacting with 
> things like competition and selection. Unfortunately, I'm not sure that I 
> have the expertise to attempt any associations with climate or other 
> factors right now. But it's likely there's something of interest going on, 
> even if we don't know what it is!
> I'm attaching a visual representation of the CBC data to this post. I 
> color-coded each of the cycles. The x-axis shows passage of time with the 
> far left side being 1950 and the far right being 2017. On the y-axis is the 
> CBC count data, with lower values on the bottom and higher counts up 
> higher. Note that the red dots, spanning the years 1950-1984, represent the 
> longest and slowest decline. The last 2 declines (the second of which we're 
> currently in right now) occurred on much smaller time scales, from 
> 1985-2000 (black dots) and from 2001-present (blue dots). The lowest ever 
> count in the entire data set was in 2016 with only 177 House Sparrows 
> reported.
> While it's likely that a population ecologist could point out several ways 
> I've poorly described these patterns, I think it's cool that Diana began 
> all this with an analysis of publicly-accessible data and shared it on a 
> bird listserv. Thanks a lot to all of you for reading this, and I'd love to 
> continue the conversation if anyone is interested!
> Good birding,
> Doug Eddy, Laramie, WY
> <>

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