The birds and the bees

Pollinators face an uphill battle amid climate change

Feed the birds (and bugs):
To aid pollinators, Kristina Schierenbeck recommends adding flowering native plants to your yard—and consulting the Mount Lassen chapter of the California Native Plant Society ( to determine which species.

“The thing that alarms me most is the lack of alarm.”

Kristina Schierenbeck, a biology professor at Chico State, has spent the past few years vigorously sounding a warning bell about the loss of wildlife to the effects of climate change. She wrote a book, Phylogeography of California, placing the phenomenon in scientific-historical context and continues to educate about the plights native flora and fauna face.

Not all audiences are receptive. She receives push-back from people she calls her “conservative friends” who repeat the same refrain: Why aren’t you as concerned about humans?

The answer: She is. From grasslands to hummingbirds, bees to farmers, nature comprises connections—“and sometimes we don’t understand the complexities of the ecosystems we’re damaging,” Schierenbeck said.

“We depend on the plants and animals, particularly in a place like Chico, where almonds are such a part of our economy and we’re seeing such a catastrophic decline in pollinators, yet we’re not restoring natural habitat in this region.

“I don’t get it. I truly don’t understand.”

Pollinators—bees, butterflies, hummingbirds—are vulnerable to climate change, at least in part because the plants they pollinate tend to be susceptible to climatic impacts. Less than 1 percent of California’s grasslands remain, Schierenbeck said, “and this is where a lot of wildflowers would have occurred. We don’t have that buffer to be able to recover, so there are no places of refuge for organisms—plant or animal—to be able to survive or wait out the drought.”

Fragile species don’t survive heat and drought; heartier species adjust their flowering, sometimes out of synch with their pollinators. Scarcity and “desynchronization” present “a double whammy” for which it’s difficult to adapt due to the rapidity of climate change.

“Organisms cannot respond evolutionarily,” Schierenbeck continued, “[because] this kind of extinction is not natural.”

Timing strikes at the heart of the interaction between pollinators and plants. The scientific term is “phenology”: the influence of climate on life events. These include roses budding, bees growing active and birds migrating.

“There seems to be mounting evidence that plant phenology—both leaf phenology and flowering phenologies—is responding to, changing with, climate changes,” said Chris Ivey, a Chico State biology professor whose research includes evolutionary ecology and plant-insect interactions.

“In almost all plants, there’s an acceleration with warming so the phenology is advancing: plants are flowering earlier, leafing out earlier.”

What about pollinators’ habits? Scientists around the world, Northern California included, are tracking the insects and birds.

“It does seem for the most part that phenologies of plants and pollinators are changing at a similar rate,” Ivey said, “but it’s not universal. There are some pairs of plants and pollinators that seem to have responded independently.

“There’s really not that much known about how these shifts are likely to impact the long-term viability, either for plants or pollinators.”

A key consideration is what Neal Williams calls “plasticity.”

Williams, an entomology professor at UC Davis, studies pollination ecology with a focus on bees. By plasticity, he means the degree to which a plant or animal can alter its phenology. (“Bug bursts” represent an example of plasticity, since the insects collectively emerge to coincide with specific conditions.)

“Whether or not they will be able to adapt to ongoing stressors like availability of moisture … is different than what I’m talking about,” Williams explained, distinguishing these changes from evolution. “There’s a certain ability of the organisms to be able to adjust that will buffer them potentially, but not forever.”

Habitat loss may be just as big a concern.

“Although climate is a big driver, it will be layered on top of land-use changes and [land-]management changes,” Williams said. “Together these things have really put the squeeze on forage availability for pollinators, whether they’re wild or managed.”

Hummingbirds face their own issues. Their diets vary—nectar and/or insects—and they have wide migration patterns that are hard for scientists to track.

Jenny Hazlehurst, a hummingbird researcher at Tulane University who lends expertise to UC Davis colleagues, says inquiries abound. Still unanswered are questions as basic as whether backyard feeders help more than hinder, and she’s pursuing opportunities to find out.

“It’s important to look at all restoration efforts on an ecosystem-wide level,” she said. “Just focusing on one group of pollinators without looking at the big picture is not necessarily the right way to do it.”