Owls react to megafire and climate trends in central Colorado
In the 1980s, when ecologist Brian Linkhart first started digging around in old woodpecker holes in Colorado for flammulated owls – fuzzy, black-eyed creatures weighing just one to two ounces – his research was all about the birds. He wanted to understand if and where the secretive little animals were breeding – questions he pursued purely because the owls fascinated him.
Not many people have extensively studied “flams,” as Linkhart calls them, because they’re elusive: The birds are nocturnal and sing for only a short span of time during mating season, and even then quietly. Linkhart has studied flammulated owls longer and more deeply than anyone, which puts his research in a unique spot to evaluate how long-term trends like warming temperatures may impact the owls. It takes decades of observation for those cause-and-effect relationships to exit the speculative realm and come into relief – and that’s exactly what’s happening with Linkhart’s data.
I the early 2000s, he first started seeing Colorado flams breeding earlier in the year than they used to. “That was one of my first clues,” Linkhart says, that the owls were responding to changes in the climate. Then he began to notice fewer offspring and evidence of siblicide in broods. More recently, these changes inspired Linkhart to examine the larger trends that could be causing them.
Linkhart has found that the earlier breeding cycle has a direct correlation with warmer spring temperatures. Precipitation declines over many years in the Manitou Experimental Forest, one of his study areas in the Pike National Forest southwest of Denver, are likely a factor in the decrease in offspring. Flams usually produce two or three fledglings a year, but over the past 15, Linkhart has seen an average closer to one. With less moisture between January and June, he thinks the shrubs, flowers and vegetation that insects – the owls’ primary food source – depend on, aren’t growing as abundantly as they used to and support fewer insects. That makes for hungrier flams. Increasingly parched summers have also made a major predator, red squirrels, more aggressive. With trees producing fewer seeds for squirrels to eat, the rodents have been pillaging flam nests more often than usual, to feast on eggs.
These temperature and precipitation trends may be a result of the last half-century of climate change, though it’s difficult to prove. Either way, future climate change will no doubt exacerbate the trends.
Another piece to the puzzle of earlier breeding and fewer offspring is fire and forest management. As wildfires increase in frequency and intensity – scientists predict that by midcentury, fire season will be about three weeks longer and start earlier – the owls’ ponderosa pine habitat may become more threatened by fires that incinerate whole stands of trees. One of Linkhart’s four study areas, each six to eight miles in circumference, includes a stand severely burned in 2002’s massive Hayman Fire. He has no pre-burn data, but his team has seen an influx of owls in unburned areas in the Pike National Forest since the fire.
Megafires like the Hayman that level big swaths of forest send flams – and other wildlife – in search of new homes. Fewer flams return to burned areas after their winter migration to Mexico. Those birds that actually have come back to the Hayman burn scar are isolated in small pockets of surviving trees in between the most-severely charred areas. That’s not to say all fires are harmful for the species. Smaller fires that clear young trees are actually key to maintaining ideal habitat for flams, which usually prefer older, spacious ponderosa and douglas fir stands.
Flams like “pre-settlement conditions,” Linkhart says, where small fires were relatively common, keeping the forest open. The birds have fewer offspring in younger stands of trees, and as Linkhart points out, flams struggle where forest managers have actively suppressed all fire, including natural, small ones, allowing forests to become overcrowded with younger trees. Not only has the past century of suppression likely resulted in lower-quality habitat for flams, but it’s helped precipitate this era of megafire.
One fire suppression method that could actually be a boon for the owls in this part of Colorado is tree thinning. Linkhart says that it’s still unknown exactly how it affects most wildlife, though he’s preparing to study its impact on flams. Parts of the Pike National Forest have been slated for thinning, “but the Forest Service money has been drying up,” Linkhart says, and the agency put the project on hold. So the professor is collecting pre-thinning data in the meantime. If thinning mostly targets young trees that have sprung up in the absence of fire, then it might be beneficial, performing the same service small fires would had larger suppression efforts not made them scarce.
It’s clear that flams are challenged by changes in climate, but overall health of populations in the Rocky Mountains and across their range, which runs from the Pacific Northwest to Mexico, is still largely unknown. Their migration route was only confirmed a couple of years ago, when Linkhart and a group of undergraduates outfitted several flams with dime-sized geolocators that tracked their journey, which covered a thousand miles or so between central Mexico and the U.S.
This May, a handful of Colorado College students will venture into the Pike forest to expand the narrative Linkhart has pieced together since he first got hooked on flams as a junior at Colorado University in Fort Collins. This summer, as in previous years, he’ll teach students to mimic the males’ call, look for tagged birds returning from migration, and take turns on night watch to document the owls’ nocturnal flutterings in and out of their nests. Some lucky members of his team will witness a fledge – when a young flam leaves the nest for the first time and crashes to the forest floor, a plume of grey fuzz and a data point in the making.
Tay Wiles is the online editor at High Country News. She tweets @taywiles.