Where Are All The Birds? The Lingering Effects of 2020
|Rufous-crowned Sparrow by Greg Lavaty
While chatting with Tucson Audubon’s Conservation Biologist Jennie MacFarland late in 2021, I remarked to her that I hadn’t seen any Rufous-crowned Sparrows that year, even though I was attuned to the species and often in excellent habitat for them. She replied that she also couldn’t remember any and that she had also not seen any Canyon Wrens that year. These are two common birds in Southeast Arizona, did we miss them—or was there something else going on? We did a little digging and what we found stunned us.
|Canyon Wren by Mick Thompson
For the last several years, I have been excerpting data from eBird to generate annual reports on all of Arizona’s Important Bird Areas. I also track the weather at these sites and some trends appear, such as Montezuma Quail populations/detections being inline with rainfall. Pulling the weather data for the last 40+ years for Tucson, you don’t have to be a statistician to see the obvious trends in our area. Looking at temperature first, you can see that global warming is not a myth, in fact our average annual temperatures here are rising at perhaps twice the global rate! Why? Looking at annual precipitation for this same period, you see the evidence for prolonged drought, our area is getting on average a few less inches of rain every year and that decreased humidity has allowed our average temperatures to soar.
In the chart on precipitation you can also see the catastrophic 2020 drought year, the lowest precipitation on record for this period. So, while we didn’t directly see the impact on many bird populations that year, this could be the cause of our perceived decline in Canyon Wrens and Rufous-crowned Sparrows in 2021.
Is the decline real? To dig deeper, I downloaded all of the eBird data for our three southern Arizona counties for 2019 (pre-drought), 2020 (drought), and 2021 (recovery). In this table, you can see the results for all species presented as the fraction of checklists that a species was detected in (first three data columns), then the changes in those data for 2020 and 2021 vs. 2019. While the effect in 2020 (the drought year itself) is not all that noteworthy, it’s in our anticipated “recovery” year of 2021 that we really see the dramatic impact of the drought on many species.
Looking at Rufous-crowned Sparrow, we see a >40% decrease in observations for this species, and with Canyon Wrens, we see an incredible >75% reduction in 2021. So these apparent population effects are very real, but it is not limited to just these two species, as quite a number of species are showing big decreases (highlighted in red in the reduced table above). The number for Elegant Trogons of >60% closely parallels our targeted survey results in 2021, and we also see that Rose-throated Becards are down >90% as well. So while many of our Mexican migrant species took a big hit in the drought, so did many of our permanent residents including Hutton’s Vireo, Black-tailed Gnatcatcher, Bewick’s Wren, and Cassin’s Sparrow. It seems many of the most affected species are smaller, year-round residents (i.e. non-migratory). With smaller territories and little ability to wander and escape the drought, they were devastated.
What is most disconcerting about these losses is that we are still seeing the effects into 2022. While Birdathon is not the most scientifically controlled study, we and other teams have noted this year that many of these species have been difficult to find. In Madera Canyon, our team spent long periods without any birds at all and completely missed common species like Canyon Wren, Spotted Towhee and both juncos. Similarly, many field trips are having a difficult time finding our favorite target birds.
|Spotted Towhee by Martin Molina
The question now is not whether the drought affected our local bird populations, or even when a recovery is going to happen, but will it ever happen? Is this what global warming looks like in the Southwest, not a gradual, almost imperceptible loss of birds from year-to-year, but catastrophic drought effects where the recovery is interrupted by our continuing higher temperatures and drought? These are very important and open questions that we’ll hopefully start to answer in the coming year, aided in large part by your own observations submitted to eBird. Thanks to birders in Southeast Arizona who are creating tens of thousands of checklists, we have a robust dataset to work with in hopes of helping those species most affected. Stay tuned.
Tim Helentjaris is a retired biologist with a keen interest in the life histories and occurrence of our resident birds in Southeastern Arizona.