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, [email protected] 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> > > > -- You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/cobirds/92bb6b6e-0d8a-4d7a-8cc9-a44ea0fb5331%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
