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.