Date: 4/13/18 7:47 pm From: <wwillem...> Subject: [cobirds] Re: What CBC data can tell us about House Sparrows in Colorado Springs
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 others?
Willem van Vliet-- Boulder
On Friday, April 13, 2018 at 12:52:32 PM UTC-6, <doug......> 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 > > > <https://lh3.googleusercontent.com/-W4ZLspoVpXs/WtDp4O0kJaI/AAAAAAAAEHs/uDW1KB6HAxM4nTqWldzLFY3x87o-QtHxgCLcBGAs/s1600/HOSP%2BCBC%2BCol%2BSprings.png> > > >