Curious about the smaller raptors of North America? Look no further than the Flammulated Owl. Residing in the western United States and Mexico, these beer can-sized owls are perfectly camouflaged to match the ponderosa pine and mixed woodlands they call home.
Stunningly patterned in gray with rusty flashes and black streaks, Flammulated Owls are rightfully a top target for many birders. But their cryptic coloration makes them challenging to find, especially during the daytime. As a result, they were once considered uncommon to rare on the landscape. However, they may be more common than birders think. Yet, despite their probable abundance, we know very little about much of their life history, resulting in a critical data gap that could threaten their presence in the West.
Fortunately, that gap is closing. Thanks to scientists like Dr. Scott Yanco, who has deployed numerous transmitters on Flammulated Owls. We are now gaining critical insight into the migration ecology of these remarkable raptors, uncovering their mysterious lives.
Understanding where birds originate and migrate through tracking can help determine the causes of population change. For instance, due to carryover effects, populations declining on the wintering grounds could result from what we do on breeding grounds. “We don’t know when, where, and how these species are dying,” says Yanco. So, for Yanco, tracking Flammulated Owls has direct implications for their conservation. Light-level geolocator tracking data is one piece of the puzzle in this effort, with eBird, banding (limited), and isotope data, as well as GPS tracks helping fill in the gaps.
“Three billion birds gone in fifty years makes me nervous,” says Yanco, referring to the seminal 2019 paper published in Science, which details the staggering decline of North America’s birds since 1970. “Studies like this rely on well-sampled species, and in the results, it is clear that common species are declining,” he says. Unsurprisingly, Flammulated Owls, like many secretive and nocturnal species, are poorly sampled, and researchers like Yanco genuinely do not know if their populations are increasing or decreasing. Approximately 2.5 billion of the birds in the study were from migratory species, including other raptors, so there is a valid cause for concern.
Flammulated Owls are simply hard to reach. Additionally, their diminutive size has made tracking them difficult until recent advances in miniaturization have made trackers small enough. The resulting knowledge gap was immense, leaving researchers to debate essential elements of their life history, including facts as basic as their diet, which we now know primarily includes moths, as well as grasshoppers, crickets, and beetles.
However, our understanding of Flammulated Owls changed in 1981, when Yanco’s undergraduate mentor, Dr. Brian Linkhart, started studying the species in Colorado. Their diet was not the only life-history trait that caused debate amongst researchers and curious naturalists. For example, what happened to them in the winter? Did they go into torpor? If so, where did this happen? As Yanco and his colleagues later revealed to science for the first time, Flammulated Owls migrate long distances to Mexico annually, with some birds reaching Guatemala. According to Yanco, future research may reveal their wintering in other Central American locales, such as the pine highlands of Belize or possibly Honduras. But for now, that is purely speculation.
This research stands out as some of the only migration research on this species. Banding records are slim, with the USGS Bird Banding Laboratory only showing a few banded individuals recaptured between 1913 and 2017. According to Yanco, perhaps only three true re-encounters as of 2019. For Yanco, this comes as no surprise, as Flammulated Owls are a low-density, highly nocturnal species. “Think about how many well-studied species researchers catch at MAPS (Monitoring Avian Productivity and Survivorship) stations. Even with these factored in, it takes something like 2000 captured birds across all taxa to gain one incidental capture later,” he explains.
Yanco’s research focuses on migration and aims to understand how and why migration emerges across different species, ultimately using this information to inform conservation decisions that protect wildlife. “Tracking is the thing we need the most. We don’t know where most species are going,” says Yanco. “We need to know how they link the areas they use over time.” Like all migratory species, Flammulated Owls need healthy ecosystems throughout their full annual cycle, including their breeding, non-breeding, and migration periods. “To best protect these ecosystems and habitats, we first need to see how they are connected,” Yanco claims. “You can’t protect breeding grounds alone as individuals live and survive across the annual cycle.”
In 2021, Yanco and his colleagues published evidence of environmental factors influencing the migrations of these diminutive owls. Their research suggests that Flammulated Owls seek relatively stable food resources during migration and the non-breeding season, matching closely to the conditions they experienced while breeding. In other words, Flammulated Owls like to keep the relative available resources around them constant. This strategy makes sense, especially considering their prey base of insects, which are only active under certain conditions.
To understand the relative prey availability to the owls throughout the year, Yanco and others used satellite-based measurements of the Earth that are known to correspond to insect abundance and activity. The first is nighttime temperatures, and the other is a measurement of how green the Earth’s surface is, which tells researchers a lot about how productive an ecosystem is, including how many insects are present. For Flammulated Owls, resource conditions do not vary much during their migrations from the Rocky Mountains to Mexico and back. Leaving the cool, dry, montane forests of a place like Colorado, Flammulated Owls must travel across increasingly isolated mountains surrounded by vast arid lands as they fly south. “From our research, we determined that Flammulated Owls are trying to track their niche throughout their full annual cycle,” says Yanco. However, while the research of Yanco and others has helped to illuminate these owls’ substantial migrations, there is also a year-round resident population in Mexico in the comparatively early stages of research.
For this study, Yanco and others deployed 63 trackers across five sites in four states (Colorado, Idaho, Utah, and New Mexico) between 2016 and 2019. At the time, the tags they deployed were new archival GPS tags. They were experimental PinPoint-8 or PinPoint-10 tags, commercially available from Lotek but not widely used. “These are cool pieces of technology. They are tiny at around one gram each” about the weight of a paperclip or dollar bill. “Flammulated Owls are about 60 grams, the weight of a C-battery. In other words, these are tiny owls, and they need small tags.” One of the main challenges with deploying such small tags is that you must catch the bird again to retrieve the tag and its data, usually the following year. Thankfully, male Flammulated Owls have a strong tendency to return to a previously occupied location. “Males never undergo breeding dispersal,” claims Yanco. “So, if they’re caught and survive, we would almost always find it again within a few hundred meters of where it was.” On the other hand, females sometimes move far enough away that Yanco and his associates have chosen not to tag them due to the difficulty of recapturing them again.
To capture owls for his research, Yanco used two different methods. “If we were working in a new area where we didn’t know where owls were, such as our work in Idaho, New Mexico, and parts of Colorado, we would first broadcast playback, stopping every quarter to half mile, listening for a response. We would then set up mist nets with an active lure.” Because Flammulated Owl males are territorial, they would come from several hundred meters away, attracted by the low hooting of an .mp3 owl. The probability of recapturing a bird was much higher if Yanco worked in a known nest area. But finding a nest is challenging work. In a place like the San Juan Mountains in southwest Colorado, Yanco and his associates could check 1000 to 2000 cavities and maybe find ten Flammulated Owl nests. The results were the same even at familiar study sites like the Rio Grande National Forest on the east slope of the mountains.
In Flammulated Owls, males are responsible for the energy needs of the female and the nestlings. Like all other forms of raptors, these owls are single-prey loading, meaning they only capture and carry one prey item at a time. Therefore, many trips back and forth to a nesting cavity are required for a species specialized in eating moths and beetles. Fortunately for Yanco, these foraging trips provide many opportunities for capturing an owl. “Once a nestling hatches, these foraging trips will happen as frequently as once per minute.”
But more opportunities to capture the owl do not necessarily mean it is any easier. “There’s a lot of ways not to catch a Flammulated Owl!” exclaims Yanco. “You let the male fly in, enter the nest, and quickly swing the net over the hole.” But as Yanco points out, this is much harder than it sounds, especially at night. “The pole can sometimes be up to 50 feet long, and sometimes you may have to hold the pole up for an hour or more,” says Yanco. “It is in the middle of the night and dark out, the pole is heavy, and you’re tired. And once they fly out of the nest and into the bag, you have to quickly work to get the net down to secure the bird.”
Scientists have discovered that large, old trees on the landscape are vital breeding grounds for Flammulated Owls. Sadly, this park-like forest habitat is threatened across their range. In Mexico, where the migratory Flammulated Owls overwinter—and a resident population lives year-round— threats such as logging place significant challenges upon these systems as the owls’ favored trees are the same trees targeted by the timber industry.
In the United States, two significant threats are urban encroachment and climate change, which at times work synergistically to compound the adverse effects of things like forest fires. Historically, forest fires in the region were relatively low in severity but high in frequency, and the vegetation responded by becoming fire-dependent. Unfortunately, the fires no longer burn as they did in the ever-increasing wildlands-urban interface. Fires are becoming more severe and more frequent. According to Yanco, the five largest fires in Colorado history have all burned in the last 20 years. For Flammulated Owls, these modern-day megafires can devastate large swaths of quality habitat in a relatively little amount of time, making the forests they call home unsuitable to occupy.
Yanco ways we need to restore the physical structure of forests that enables native fauna to persist, which is a big challenge. How to do so is another question. “It is too expensive to mechanically thin the forests to reduce fire as one of the largest threats. Now, with fire interlacing with the wildland-urban interface, it is a huge challenge.” Yanco continues. “I fear that ecosystem as we know it is itself threatened.”
In the future, Yanco is hopeful Motus or Icarus tags will be deployed on Flammulated Owls, giving greater precision and—most importantly—never requiring the researcher to recapture the bird to retrieve data. Yanco also relays his strong belief in collaboration, noting his hope to work further with colleagues in Mexico in determining what is happening on the wintering grounds for Flammulated Owls as well as the resident population. He is also keen on making data open access, contributing to large-scale outreach and conservation efforts like Audubon’s Migratory Bird Initiative. “We now have billions of animal locations from these amazing new tracking devices. By sharing data with efforts like the Migratory Bird Initiative, scientists can contribute to large-scale projects like the Bird Migration Explorer that allow us to understand ecological patterns at huge spatial scales and across species. The insights these types of projects promise will be invaluable in addressing the twin challenges of climate change and biodiversity loss.” Yanco encourages researchers to put their data into practice. “I believe researchers can do more applied outputs with their work.”
Like many who research the migrations of North American birds, Yanco acknowledges the role of the Migratory Connectivity Project (MCP) in the success of his research. “[Co-founder of the MCP] Pete Marra was on my graduate committee, we connected through research, and eventually, MCP provided tags, support, advice, and collaboration. MCP was essential for the success of deploying transmitters for multiple sites.” Yanco also recognizes the role of his Ph.D. advisor, Dr. Mike Wunder, in the success of this publication as part of his dissertation.
Dr. Scott Yanco is currently a Postdoctoral Associate serving a dual appointment at the Max Planck – Yale Center for Biodiversity Movement and Global Change and the Department of Ecology and Evolutionary Biology at Yale University (since 2021). For up-to-date information about his research, please visit his website at http://www.scottyanco.com.