[Tweeters] Toppenish CBC Long-term Trends

Eric Heisey magicman32 at rocketmail.com
Thu Feb 11 21:01:25 PST 2021

Hi all,

Sorry for the second post; I meant to post this a while ago but just realized it never sent. Over the past year or so I have been occupied with analyzing long-term data from a demographic study population of study population of Savannah Sparrows from New Brunswick in order to write an honors thesis. As I now bear the know-how, I took this year as an opportunity to analyze some of the long-term trends of species observed on the Toppenish Christmas Bird Count. I thought they may interest some of you, so below is a portion of my annual summary outlining the trends I found. I have made a variety of figures that I am unable to attach due to the 25KB post size limit on tweeters, but if you are interested, feel free to contact me and I am happy to send them along.

The last few years have seen low counts of Black-billed Magpie, Mourning Dove and Western Meadowlark on the Toppenish CBC. Western Meadowlark seems to be showing the one of the most obvious declines, with a steady decline of about 2 birds per year since 1983. Given the imperiled nature of North American grasslands, this unfortunately does not come as a huge surprise. Black-billed Magpies have also been steadily declining for the duration of the count, averaging a decline of 6 individuals per year since 1983. Magpies were actually pretty stable until about 2008, with an average count of 439 per count between 1983 and 2008. However, since 2008, that average has dropped to just 204 individuals per count, less than half of the average in the first 25 years of the count. We tallied 350 Magpies this year, the most since 2008, so perhaps they will rebound, but this is still below the average of the first 25 years, giving us cause for concern.

Mourning Doves are an interesting enough case to get their own paragraph. Between 1983 and 2011, the annual count of Mourning Doves was actually increasing by about 3 individuals a year. Can you guess what happened in 2011? Enter the Eurasian Collared-Dove. This Eurasian invader was first recorded on the count in 2009 and began to really become established in 2011, eventually skyrocketing to a high count of 689 in 2017, less than ten years after their first detection. They have averaged a growth of 30 individuals a year since their establishment. I have heard varied opinions as to whether people think Collared-Doves are negatively influencing Mourning Dove populations. Most people I’ve talked to seem to think they are coexisting well. However, our count data may paint a different picture. Since 2011 (when Collared-Doves took hold), Mourning Doves have declined by roughly 43 individuals a year. 43!!! That’s seriously concerning. Now, it is worth mentioning that Mourning Doves appear to oscillate cyclically, with dips in their population every 3 to 7 years. We still need more data to show that there is a direct correlation between the increase of Collared-Doves and decline of Mourning Doves. However, it’s been 9 years since the establishment of Collared-Doves now, and outside of a one year spike in 2016 (which was an abnormally cold and snowy year; I wonder if this makes it slightly anomalous and could have forced Collared-Doves out of the valley), Mourning Dove numbers have not seemed to rebound. There are a number of other factors that could be contributing to this trend, but anecdotally, I feel like I am seeing many fewer Mourning Doves than I used to around the Yakima Valley, while I just seem to be seeing more and more Collared-Doves. This will be something to watch closely in the coming years.

On this topic, do any of you know of a way that I could easily access the long-term records of other CBCs from across the state so I could do a similar analysis on the statewide basis? It would be very interesting to see how this trend is acting across other counts. I suppose it is possible that this could be a regional trend, as perhaps Collared-Doves, which seem to thrive in the presence of the growing hops industry, could be proliferating more-so than elsewhere given the ever expanding agriculture of the Yakima Valley. I appreciate any tips you you may have!

There have also been a number of species that have seen an increase in their numbers over the course of the Toppenish CBC. Red-tailed Hawks, for example, have been increasing by roughly 2 individuals a year since the inauguration of the count. Bewick’s Wrens and Spotted Towhees have also become more common over the last 37 years, growing by about 1 and .5 individuals a year respectively. However, these increases may be linked to our overwhelmingly negative impacts on the planet. Red-tailed Hawks may be increasing due to the increase in land cleared for agriculture, as they coexist well with our human developments. Similarly, Bewick’s Wrens are likely expanding northward, just like the Lesser Goldfinch and California Scrub-Jay, due to anthropogenic climate change and the milder climate we now inhabit. Lastly, Spotted Towhees could theoretically be increasing as continued deforestation and a prevalence of wildfires leads to the clearing of forests and a subsequent rise in the shrubby thickets they covet in the breeding season. These are all hypothetical explanations, but it’s easy to see how the growth in the populations of these species may be caused by our continual destruction of the natural world.

Hopefully these trends are thought provoking at the very least. It would be really interesting to see how the trends of these same species and others are acting on other counts. Have any of you other count compilers out there looked at trendlines on your counts? I would love to hear from you if so!

Good birding,

Eric Heisey

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