Jenny Rechel has been studying birds in the San Dimas Experimental Forest above Glendora for 19 years. These days, she's hearing fewer species come through — a result of the historic four-year drought that continues to plague the state.
“Seems like there’s fewer bird calls," the U.S. Forest Service researcher said. "I hear less calling, especially in the areas by the streams.”
Rechel relies on her ears and her vast knowledge of bird vocalizations for the regular surveys she conducts in spring and fall each year. The species and number of birds she identifies give her an understanding of population trends and how different factors, such as development, drought and wildfires impact them.
On a recent morning, Rechel was in the forest, identifying birds during the fall migration. Like a bird herself, Rechel was constantly in motion, trying to note as many birds as possible.
She said she learned to "ear bird" from her father when she was growing up in Colorado. She said he made her use binoculars to locate birds that he heard. (Can you guess bird calls? Take our audio quiz here.)
"Of course you get really annoyed, ‘I can’t see it! I can’t see it!’ And you get really frustrated," she said. "Then, I’d see the bird, and then we’d go back, and he would have me find the bird in the bird book."
A useful skill
The ability to identify a bird by the sounds it makes is important for Rechel's work, as many of the species she studies often stay hidden among branches. It is a refined skill that requires years of practice, however, due to the vast repertoire of calls that a single species of bird can make.
"Birds don’t always make the whole call. So you pull up an app, and the app will have the entire bird call on it, but when you’re out in the woods, you just hear half of it," Rechel said. "Some birds have three or four, and some birds have 10 or 12 calls. And humans can’t hear all the calls that birds make."
Rechel monitors 106 stations throughout the San Dimas Experimental Forest. At each, she gives herself a strict 10-minute window, during which she notes any bird she sees or hears within a 75-meter radius.
Caption: a map of survey plots in the San Dimas Experimental Forest (Courtesy of Jenny Rechel, U.S. Forest Service)
The birds she records are only an estimate of the numbers that come through the area, but by sticking to a rigorous experimental design for such a long time, Rechel has been able to get a solid understanding of population trends over the years.
Recently, her study has revealed that bird species diversity in the region has plunged since the onset of the current drought — in some areas by more than 50 percent from peak levels. The longevity of the decline is more significant than one seen after another major event, -- the 2002 Williams Fire that burned more than 38,000 acres in the San Gabriel Mountains.
"It’s not fire that harms them. It’s the decline in precipitation, brought on by the drought,” Rechel said.
Rechel originally only planned to survey bird populations for five or six years, but she continued, because she and local stakeholder agencies were interested in the results she was finding. She said she plans to retire after making it to 25 years of data collection.
It's her dedication that has allowed her to make the connection between drought and species declines.
"I was only able to deduce this, because I have the long term data set and multiple disturbances," Rechel said. "I know what the fire was because I was here when the fire was here. And I go to the same sites every year.”
Rechel said bird numbers may rebound in a couple of years, as a delayed result of rains expected to be delivered this winter by the strong El Niño. Her data shows a similar upswing occurred after a moderate El Niño in the mid 2000s.
However, with wide predictions that climate change will cause droughts to be more commonplace in the region in the future, Rechel said she is concerned about the future health of bird populations.
“It’s kind of — I was going to say sad, but it’s, you know, it’s kind of negative, because I like the birds. People like the birds,” she said.
Listen as U.S. Forest Service researcher Jenny Rechel performs one of her birding surveys in the San Dimas Experimental Forest. Recorded in stereo; headphones recommended.