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 

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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