By shifting nesting times, early birds adjust to climate change

As the West warms, some songbirds in California are raising their young earlier.

 

For the humans, breakfast meant waking up an hour before dawn in a tent and grabbing something quick — generally a granola bar that had frozen overnight, recalls Morgan Tingley, an ornithologist at the University of Connecticut. Then he and the other researchers would hike through forests in California’s Sierra Nevadas, listening for the peeps and trills of birds stirring in the crepuscular light. As a graduate student in the mid-2000s, Tingley helped lead the , an effort to repeat the remarkably thorough biological inventories that Joseph Grinnell, the founding director of Berkeley’s Museum of Vertebrate Taxonomy, had orchestrated across California 100 years previously. “You’d write down every single bird you could detect, by sight or mostly by sound,” Tingley recalls.

For the songbirds, breakfast meant leaving a nest or tree hollow at dawn to seek insects, nectar, fruit. The birds’ meals depend on local phenology, the seasonal timing of the cycles of plant and animal life. But as the climate has changed in the Sierra Nevada mountains, that age-old rhythm has slipped. By the time they are ready to nest, migratory songbirds often find that their food sources are available either higher up mountains or further north than in the past. For the most part, the birds follow suit. But a surprising number keep nesting in their old ranges, and until recently, researchers haven’t had a plausible explanation as to why. Now, a new analysis of the Grinnell Resurvey data suggests that many California songbird species are compensating for the effects of climate change, not by altering their range, but by nesting and raising their young much earlier in the year.

A house wren constructs its nest.
Tibor Nagy/Flickr

Nesting is an especially vulnerable time for birds. “Bird nestlings are featherless, naked, need to be incubated — which is to say, they are basically coldblooded,” says Jacob Socolar, a postdoctoral research fellow at the University of Connecticut. “They are at the mercy of whatever temperatures they are experiencing.” Also essential for baby bird health is a high-protein diet, in the form of beetles, grasshoppers and worms, which harried parents stuff down endlessly gaping beaks. This means that baby birds are temperature sensitive in another way, too: They can’t thrive if it’s too hot for the insects that they eat to survive.

For years, researchers have documented songbirds in the West moving in response to climate change. The evidence is especially thorough for northern California and other parts of the West that Grinnell explored a century ago, sometimes accessing field sites by pack train, sometimes by an old, decrepit car that he called “the machine.” Grinnell revolutionized field biology through his meticulous note taking system. “He invented the first standardized bird surveys,” Tingley says. One hundred years later, Tingley and colleagues retraced Grinnell’s and his colleague’s steps, sometimes walking the exact same trails in national parks and other protected areas. This resurvey resulted in groundbreaking findings that documented most of the songbirds that Grinnell and his colleagues encountered shifting to cooler places to nest over the intervening century. But about 37 percent were not shifting.

Joseph Grinnell's field notes from May 26, 1911, when he and his wife Hilda ("Mrs. G.") spent the morning photographing a Calavera's Warbler nest in Yosemite.
With the permission of The Museum of Vertebrate Zoology, University of California, Berkeley. Field Notes: Grinnell J. 1911 (Part 1), v1318

One explanation may lie in the birds’ timing. Socolar, who works with Tingley, analyzed the nesting behavior of more than 300 birds in California’s Sierra Nevadas and Coast Range Mountains using the Grinnell Resurvey data. He found that, on average, these birds have begun nesting five to twelve days earlier than they did in Grinnell’s time. While most of the birds have shifted their nesting locations as well, close to 40 percent have not. But by nesting about a week early, these homebody birds still get to raise their babies at about the same temperatures as they would have a century ago.

Socolar used data from , a citizen science program that records nesting success of wild songbirds across the country, to seek a connection between nest temperature and nestling survival. “It was a massive data set,” he says. “We restricted ourselves, and we had 47,000 nests.” As the researchers predicted, nestlings in cold areas fared poorly in colder years and did much better in warmer years. Nests in warm areas had the opposite fate. To Socolar, this demonstrated that nest temperatures matter for baby bird survival.

The Wilson’s warbler is one of the songbirds found in both the Sierra Nevada and Coast Range that is helping scientists understand how species respond to climate change.
Doug Greenberg/CC via flickr

Which is not to say that scientists know what is motivating these birds to nest earlier. “Is the main reason finding a good temperature to nest under? Or tracking insect emergence and the temperature story is a happy side effect? We don’t know the answer to that question,” Socolar says. Either way, the birds get both benefits. If some birds can cope with climate change by shifting their nesting time, then this research challenges a fundamental understanding of how species respond to climate change. “One core prediction that is canonical of climate change biology … is that as it warms up, they should shift to where it’s cooler,” he says. But these birds are breeding so much earlier, they may not need to.

Socolar is quick to point out that this research is only one possible explanation for why some birds are not moving their nesting locations in response to climate change. Other possibilities haven’t been ruled out yet, he says — maybe some California birds can tolerate wider temperature ranges than others, for example. As temperatures continue to rise, the future of many of California’s songbirds may depend on that answer.

Maya L. Kapoor is an associate editor for NewTowncarShare News.

NewTowncarShare News Classifieds
  • Must see for sng/extd fam or corp retreat in pines! $1,030,000
  • The American Forest Foundation seeks a smart and highly motivated candidate to join our Western conservation team. The Regional Manager supports the Regional Director to...
  • Exciting opportunity to lead the charge on meeting the future transportation demands of our community! This position will develop, coordinate, and implement the Integrated Transportation...
  • with Robert Michael Pyle September 26-30, 2018, in Missoula MT.
  • Boise State Public Radio is hiring a Reporting Fellow as part of a new nationwide collaborative, Guns & America. Based in the state capitol, Boise...
  • Middle Colorado Watershed Council. Rifle, CO.
  • RiversEdge West is seeking an entrepreneurial leader with solid nonprofit management skills to lead our high functioning team and help us make an impact on...
  • Conservation nonprofit Friends of Cedar Mesa in Bluff, Utah is hiring an Education Center Director to oversee the operation of the Bears Ears Education Center....
  • Western Resource Advocates (WRA) is seeking a talented, organized person with great people skills, who is passionate about protection of the natural environment to work...
  • The Wilderness Society is recruiting for an experienced Communicator for our Northwest Region. This position is located in Seattle, WA. For more information please visit...
  • Here is an opportunity to have a piece of self-sufficient paradise on Idaho's Main Salmon River adjacent to the largest Forest Service wilderness area in...
  • in 5-home conservation community & botanical sanctuary on 20 acres.
  • The Montana Wildlife Federation is looking for an enthusiastic and innovative Membership and Engagement Coordinator to help grow and maintain our grassroots voice for wildife,...
  • The City of Fort Collins is excited to announce a Sr Environmental Planner position within the Natural Areas Department. This position will be housed within...
  • on beautiful Snow Angel Ranch located within San Juan National Forest near Pagosa Springs, CO. Lakes, fly-fishing, swimming, hiking, mountain biking, horse trails, horse accommodations...
  • 5 acres, well. Abuts Carson NF; hike fish ski; deer turkey elk.
  • Paonia, CO - Part-time, live-out, Tues to Fri. Childcare and light housekeeping. Able to interact with children and speak English, non-smoker. REFERENCES. Contact [email protected]
  • The Marketing Director develops the strategy and leads all marketing efforts at NOLS. The director is first and foremost responsible for driving enrollment of over...
  • The Nature Conservancy, one of the world's leading conservation organizations, seeks a Program Manager to help advance our Sierra Nevada conservation and restoration efforts. Working...
  • Boise-based Winter Wildlands Alliance is looking for an experienced and highly motivated individual to organize our annual Backcountry Film Festival and Tour and coordinate additional...