The birds might disappear from parts of their range within a few decades
By Bob Berwyn
SUMMIT COUNTY — Broad-tail hummingbirds that migrate to the Colorado high country in the spring may soon find that their arrival is out of synch with key nectar-providing plants they need to sustain themselves during breeding.
Graceful glacier lilies, for example, are one of the first flowers to bloom when the snow melts, but meticulous research at the Rocky Mountain Biological Laboratory near Crested Butte shows they are blooming 17 days earlier than in the 1970s.
The hummingbirds are also migrating a bit earlier, but perhaps not soon enough — by the time they arrive, many of the nectar-laden plants have withered away. Biologists calculate that, if current trends continue, in two decades the hummingbirds will miss the first flowers entirely.
Disruption of the delicate balance between flowering and the nesting cycle could make it difficult for the birds to sustain their populations at the northern end of their range. The hummingbirds only lay two eggs per year and have a relatively short lifespan of only two years. Within a few decades they could disappear from the Southern Rockies, researchers suggest in a new study.
“This year is pretty much a record,” said University of Maryland biologist David Inouye, referring to the March meltdown, when most of Colorado’s snowpack vanished during a month that usually sees maximum accumulations.
Detailed flower counts
In 1973, Inouye started monitoring two-meter square study plots at the lab, counting all the flowers every second day, and documenting year-to-year changes about 100 species.
“Plants that flower early in the season are changing a little faster, but all of the species out here are changing their phenology,” he said, adding that, this year, the glaciers lilies won’t be producing any seeds because of the unusual winter and spring weather.
The plants are long-lived, so it won’t wipe out the population, but it could be a long-term problem, especially if similar weather patterns prevail more frequently, he said.
These rapid climate-driven changes in plant communities have a cascading effect on other species. Similar climate change effects have been observed and documented in other ecosystem interactions.
In March, Inouye published research showing how early spring warming, followed by late frosts, is affecting Mormon Fritillary butterflies. Like hummingbirds, those insects depend on certain species of early blooming flowers. When the buds are damaged by frost, the butterflies don’t have enough food.
Biologists in Antarctica have observed similar impacts, documenting declines in penguin colonies that appear to be linked with changes in the timing of ice melt and formation, which affects the life cycle of plankton and krill.
The changes are most noticeable at the “poleward limits of migratory routes, where phenological advancements in the spring are progressing more rapidly than at lower latitudes,” the biologists wrote.
The results of these studies suggest a novel hypothesis: “Some species may contract their range toward lower latitudes under continued warming,” Inouye and his team concluded. The decoupling of these complex interactions could cause entire ecosystems to collapse.
“I think that’s going to be a pretty common problem for plants and animals that interact,” Inouye said.
Timing is everything
That includes the broad-tailed hummingbirds that migrate north from Central America every spring to high-mountain breeding sites in the western United States. The birds have only a short mountain summer to raise their young.
Male hummingbirds scout for territories before the first flowers bloom. Based on observations at the Rocky Mountain Biological Laboratory, the males especially feed on the nectar of the glacier lilies, which begin to bloom about one week after the snow melts and stop blooming two weeks later.
Subsequent nesting appears to be synchronized with flowering the dwarf larkspur. Hummingbirds also appear to be important pollinators for this plant.
But the time between the arrival of the first hummingbird and the first bloom has collapsed by 13 days during the past four decades.
“In some years, the lilies have already bloomed by the time the first hummingbird lands,” said Amy McKinney, also a University of Maryland researcher.
“Northern species, such as the broad-tailed hummingbird, are most at risk of arriving at their breeding sites after their key food resources are no longer available, yet ecologists predict that species will move northward as climate warms,” said Saran Twombly, program director in the National Science Foundation’s Division of Environmental Biology, which funded the research.
Broad-tailed hummingbirds that breed farther south have fewer challenges.
“In Arizona, for example, there’s no obvious narrowing of the timing between the first arriving males and the first blooms of, in this case, the nectar-containing Indian paintbrush,” Inouye said.
Higher latitudes may be more likely to get out of sync ecologically because global warming is happening fastest there.
As the snow continues to melt earlier in the spring, bringing earlier flowering, the mountains may come alive with glacier lilies long before hummingbirds can complete their journey north.