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Thursday, October 28, 2021

Sierra Club Christmas Bird Count reveals bird ranges shifting north due to warmer year-round temperatures

Fires, heat and drought pose key threat to bird populations, which can result in an overall loss of range

Every year for the past 50 years, the Yolo Audubon Society has run a Christmas Bird Count in the Putah Creek area. Data from these bird counts provide information about trends in avian diversity. On Jan. 14, the Sierra Club gave an online presentation analyzing this data, titled “Avian Responses to Rapid Climate Change: Examples from the Putah Creek Christmas Bird Count.”  

Webinar presenter Steve Hampton described Christmas Bird Counts as “a huge citizen science data collection effort.”  

“In the 1800s, there was a tradition on Christmas Day for the men in the family to go out and have a contest to see how many birds they could shoot with a gun,” Hampton said. “Some conservationists in 1900 got together and said ‘We’re not going to do that, we’re going to count birds.’ And they created the Christmas bird count circle; it’s a 15-mile diameter circle, which adds up to around 200 square miles. Inside that circle, they’ll have teams of people go out, and they’ll count all the birds they can find and do a survey.” 
One of the most marked changes over time is a northward shift in bird ranges, which is a result of food sources becoming more available year-round.  

“Increasingly, we’re finding birds that normally winter in Mexico, or Central America—birds that we expect to see in the summer, but not in the winter,” Hampton said. “The western tanager is a bird that was never recorded on the Christmas Bird Count until 1996, and now we expect to see one or two every year, which would have been a huge rarity in the past, but it’s not a rarity anymore.”  

Western tanagers are not the only birds which have increased their range, according to Hampton.  

“The other bird that has really increased on the Christmas bird count is the turkey vulture,” Hampton said. “We used to have zero to five turkey vultures on the Christmas Bird Count, and now we have 200 to 300, because we don’t have fog that much anymore. They don’t like fog; they like to soar on the thermals, on warm air, and now that our winters are warmer, the turkey vultures are just here, all year long.”

This quantitative increase in birds may seem like a good thing, but Hampton stated that this northward shift can also result in an overall loss of range.  

“There’s winners and losers,” Hampton said. “Right now, in winter in Davis, we have a lot more birds because we don’t have freezes anymore. In Southern California deserts, they’ve seen a collapse of their bird communities, because it’s too hot and dry in the summer.”  

Fires also decrease the diversity of birds seen during the Christmas Bird Count, according to UC Davis Department of Wildlife, Fish and Conservation Biology Assistant Professor of Teaching Robert Furrow.  

“The area that I covered is a UC Davis reserve—Stebbins Cold Canyon Reserve—and it was completely burned over the last summer,” Furrow said. “The most common thing we found was the wrentit—that’s a species that’s highly localized to these kinds of habitat[s] in California: chaparral, dry scrubby habitat[s]. We saw a pair of golden eagles, but in general we had really low diversity and really low numbers this year, because this is the first year after a fire.” 

Some birds, such as the wrentit, are unwilling or unlikely to adapt to climate change, according to Furrow.  

“[Wrentits] really do not like to fly,” Furrow said. “They do fly regularly, but they don’t fly long distances. They only fly small jumps of a few feet. If their habitat is being lost, they often behaviorally aren’t comfortable flying to new areas, or if the fire becomes more frequent, and they need to leave the chaparral to find other habitats, they might just end up being too afraid to fly and literally burn up in fires.”

Hampton described birds as a canary in the coal mine for what humans will face as climate change worsens. 

“What’s happening with birds is happening fast—it’s happening faster than people realize, and that’s probably because birds are so incredibly mobile, so it’s just kind of a symbol of what humans are facing,” Hampton said.  

Hampton stated that the changes in climate are “exactly what happened 55 million years ago, with the Paleocene-Eocene Thermal Maximum, which was this massive global warming event. The problem now is that the climate is warming at 10 to 20 times the rate of that change.”  

Furrow also emphasized the concerning speed of climate change.  

“Evolution is on a timescale of generation time for organisms,” Furrow said. “So for birds or mammals, that’s many years. Evolution needs to occur over thousands of generations, that’s thousands of years, whereas the changes we’re making are over decades or centuries, which is much faster.” 

Written by: Rachel Shey — city@theaggie.org

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