Re: [cobirds] What CBC data can tell us about House Sparrows in Colorado Springs

Hi again,

After beginning some attempts at correcting for effort (thanks for pointing that out, Joe Roller!), I'm still playing with different ways to quantify things. I can share two possible points of interest:

--Diana's suggestion that the 2016 count may have been low due to poor weather and thus participation doesn't seem to be reflected in the data; the effort for 2016 was much higher than in 1953 (for example), when only half the number of people recorded the highest count in the Colorado Springs dataset, 1476 birds! There were many years with less effort and more birds, which leads me to believe the low count in 2016 might very well reflect a real population thing going on.

--I did a very simple regression of number of participants vs. year. As you can imagine, participation goes up over time. But it's the rate that's the fun part: The Colorado Springs CBC adds almost exactly 1 person every year!

Cheers, birds, and amateur data analysis,

Doug, Laramie, WY

On Fri, Apr 13, 2018 at 1:00 PM, Diana Beatty <otowi33.33@gmail.com> wrote:

2016's low count is likely a product of the weather that day - we had a blizzard with temps around 0 degrees Fahrenheit - some areas of the circle may not have had the usual level of participation due to that weather, as well.  In reading all these posts a few questions that occurred to me were 1. Is there a successional change in habitat at some of these feeders where people are now reporting lower numbers that could be at play?  Newer housing developments tend to have slightly different habitat than more established ones, for example.  2.  Is there any relationship between the success of EUDO in traditional House Sparrow habitat and House Sparrow population fluctuations?  Incidentally, I have not noticed decline in the Security/Widefield/Fountain area but I haven't been keeping close data, either.

Diana Beatty

On Fri, Apr 13, 2018 at 11:34 AM, <douglitas@gmail.com> 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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******

All that is gold does not glitter, not all those who wander are lost; the old that is strong does not wither, deep roots are not reached by the frost.

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Doug Eddy

PhD student, Carling Lab

Program in Ecology (PiE)
Department of Zoology & Physiology
University of Wyoming

www.carlinglab.com

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