the awe he felt seeing migrant songbirds resting at a reserve on High Island, a peninsula on the Texas coast near Galveston. At the time, Frank Thompson was just beginning his work as a USDA research wildlife biologist and adjunct professor at MU — positions he still holds almost three decades later. It was April, an ideal time to watch migrants arriving from across the wide Gulf of Mexico. Seeing the great streams of birds, exhausted from their long journey, made a lasting impression.

“Being there on a day when hundreds of birds arrive from non-stop flights crossing the gulf… it is pretty incredible to witness,” he says.

Sadly, it’s an experience that may be denied future generations. In the 30 years since Thompson made that memory, songbird species have declined precipitously, some to the point of collapse. The North American Breeding Bird Survey — a mostly volunteer effort that since 1966 has been the leading source for long-term, large-scale-abundance data for more than 400 North American bird species — reports that almost half of the survey’s 239 songbird species have significantly declined.

Earlier this year, Thompson contributed to an important evaluation of data that could help scientists better understand why. The study, published in The Journal of Wildlife Management, sheds light on what may turn out to be a crucial driver of songbird declines — high mortality among juvenile birds.

“A major finding was that the first three weeks when these songbirds are out of the nest is, in fact, a period of very high mortality,” Thompson says. “It isn’t a universal explanation, but it is a potential contributing factor for declines in some birds.”

Thompson has devoted his career to researching potential causes of songbird decline and developing targeted conservation strategies. One conservationist who uses his findings is Jane Fitzgerald, Central Hardwoods Joint Venture coordinator for the American Bird Conservancy, a non-profit dedicated to the conservation of wild birds and their habitats in the Americas.

“Our partnership’s job is to get habitat on the ground to help declining bird populations,” Fitzgerald says. “We use the best available science to decide what kind of habitat needs to go where, so for more than 10 years now, I’ve been going to Frank. He’s not just doing science for science’s sake. He’s doing science to give to managers and people like me who are trying to get things done, so his work is very informative to actual on-the-ground conservation work.”

Thompson arrived at MU in 1983 as a doctoral student, having completed his bachelor’s degree at Rutgers University and master’s degree at the University of Vermont. After earning his Ph.D., he “very luckily” got a research job with the USDA Forest Service in Columbia, and soon after, joined the MU faculty. It was a good time to be starting a career in bird research because by the late 1980s, thanks to analysis of the North American Breeding Bird Survey, word was out that many birds were experiencing significant declines.

In the beginning, scientists and conservationists drew what seemed to be the obvious conclusion that the declines were linked to habitat loss. Declining tropical forests received the most press, but there was also concern about changing habitats here in the U.S. — and that was where Thompson began his investigations.

Runoff Collector

ready to take wing
Left: Eastern Phoebe nestlings ready to "fledge," or develop wings capable of flight, near Augusta, MO. Photo by Danny Brown. Right: In the Baskett Research Forest near Ashland, MO., MU student researcher Julianna Jenkins uses a stick-mounted mirror o check on an Acadian Flycatcher nest. To study juveniles, researchers such as Jenkins need to acurately predict when nestlings will fledge. Photo by Freeman Jenkins.

“Very early on, our lab — working with some other people here and in other universities in the Midwest — detected a pattern that nest success was less where forested habitats were fragmented versus where habitats were large and contiguous,” Thompson says.

That research received international attention in 1995, when it was published in the journal Science. Thompson was the second author on the paper. It reported that nest success for some forest bird species was low enough in fragmented forest landscapes to create population “sinks,” or areas where local reproduction was insufficient to compensate for adult mortality.

While research indicated one cause might be higher nest predation in fragmented areas, Thompson had little direct evidence to determine which predators were to blame.

“That turned out to be a much harder question to answer,” he says. The clues predators left at the nest usually were not enough for researchers to make a positive identification. They needed a way to catch the predators in the act, and Thompson and his MU team came up with an ingenious solution: security cameras for nests.

“Our lab helped pioneer the use of miniature video equipment to monitor nests,” Thompson says. They began using video surveillance in the 1990s.

Today there are hundreds being monitored by video in Missouri and Texas, he says. The footage reveals that the most common nest predators are snakes and other birds, among them raptors, cowbirds and jays. Rodents and other small mammals, such as raccoons and squirrels, are also a threat. The research also revealed these predators are a greater problem for birds nesting in fragmented landscapes.

“This had conservation implications because now we could suggest that we need to conserve large, non-fragmented forests to support populations of forest and shrubland birds,” Thompson says. He adds that others at MU, including biological sciences professor John Faaborg, an internationally known ornithologist and author of the reference book Saving Migrant Birds, had done similar work with grassland birds and come to a similar finding — that their nests face less predation in large grasslands than in fragmented landscapes.

It’s research Fitzgerald has used often. “We promote restoration of habitat in ecological subsections that are the least fragmented,” she says, “because we want to put new habitat in the good landscapes.”

Having solved important riddles about nest productivity, Thompson began to wonder about the next stage of birds’ lives, the fledgling period — that span of time when juvenile birds begin to leave the nest but are not yet completely independent. That was a stage of songbird life that, until the late 1990s, had mostly been ignored.

“And for really good reasons,” Thompson says, explaining that gathering data on birds in this stage was nearly impossible until the advent of super-small radio transmitters, devices light enough not to hinder young birds just learning to fly.

After the technology arrived, MU researchers were once again among the first to make use of it. Thompson and Faaborg co-advised a master’s student, Angela Anders, whose published research was among the first to use radio-tracking data to document habitat use and survival rates for juvenile songbirds.

Over the next decade, the juvenile stage attracted a few dozen studies — still far less than the nesting and adult stages. But it was enough that, two years ago, Thompson and Andrew Cox, a post-doctoral student at MU, joined two other colleagues to take a look. Their goal, Thompson says, was “to summarize what we had learned to date, and to ask: ‘What do we need to do next? Do we need to put more emphasis on juvenile survival from a conservation perspective?’”

The team focused the review on species survival rates and the factors affecting those rates, as well as how those rates impact population growth or decline.

After collecting 53 studies, Thompson’s team compiled estimates of juvenile survival for 37 species in the passerine order, which includes birds with feet adapted for perching, a characteristic of all songbirds. Averaging across species, they found about 60 percent of fledgling birds survived the juvenile stage; for some species, the rate was much higher; for others, much lower.

To determine whether juvenile survival rates could be having a significant effect on population decline for specific species, Thompson’s team used a two-stage population model that factored in three key areas: annual adult survival of females, survival of female fledglings to the following breeding season, and the number of female fledglings produced per female per breeding season.

Thompson says the results were telling. For some species, he says, juvenile survival rates were low enough to be “a very plausible driver of a population decline.”

While that answered the question of whether this stage needed conservationists’ help, it did not address what form that help should take. That answer depended on which factors were impacting survival rates and how. The literature covered several factors impacting survival, from species traits to weather. Thompson’s review revealed age consistently had the greatest significance: In the first three weeks, every additional day brought a dramatic increase in survival rates.

Threatened From the Ground Up

threatened from the ground up
Left: Graduate-student researcher Andrew George employs radio-telemetry to locate the whereabouts of a Western Ratsnake, Pantherophis obsoletus, an important predator of nesting birds. Such systems allow researchers to gain a wealth of information on animal movements and habitat use by mapping locations through time. Photo by Andy Meuller. Right: Undergraduate research technician Shae Anderson watches a ratsnake climb a tree near a monitored Acadian Flycatcher nest. Photo by Julianna Jenkins.

“The birds obviously started to develop better life skills, like how to fly and escape predators or what’s good habitat and where to find food,” Thompson says.

The review also identified habitat as a notable factor and the one with “the biggest conservation implications,” Thompson says. “A lot of studies found support for at least one habitat factor. Those are the kinds of things we can manipulate to eventually increase survival to benefit birds.”

Although the different studies looked at different aspects of habitat, one common theme emerged: Fledglings that quickly moved into thick cover were better off. “Birds that could get into shrub thickets and very dense forests, they survived better,” Thompsons says.

This finding confirmed research by two graduate-student members of Thompson and Faaborg’s team. And while the habitat need wasn’t brand-new knowledge, the fact that it had been found in several studies was news. “Because we see these common patterns, we now have more confidence in what is happening than from any individual study,” Thompson says.

The review also gave Thompson and Faaborg direction for new research. They currently have a graduate student investigating how habitat choices affect survival of fledgling Ovenbirds and Acadian flycatchers.

“It is important for conservation groups and land managers to know exactly what types of habitats need to be provided in order to protect these birds,” Thompson says. “Providing habitats needed by breeding adult birds won’t make much of a difference if those birds don’t survive long enough to reach adulthood because they don’t have adequate shelter when they are young.”


MODELING BIRDS' FUTURE

along with continuing to research specific factors affecting bird populations, Thompson has also been developing new approaches that combine the “demographic” modeling done in the juvenile study — that is, modeling that seeks to define how various factors affect population rates — with habitat modeling exploring how various forces might influence the places birds call home.

Dubbed “landscape-based population viability models,” these allow scientists like Thompson to learn more about how different forces — such as extreme weather and land use — might be interacting with the drivers of bird population change, factors such as nest predation and juvenile survival.

The first step in developing these models is to use data from satellites, remote photography and similar sources to examine current landscapes. Next comes computer analysis that helps researchers predict how landscapes will likely change in response to known drivers of change, events such as timber harvests, commercial development, fires and even tornadoes.

“We ask, ‘If things continue to happen about the way they happen now, how’s that landscape going to look in 50 or 100 years? What’s that going to mean to the birds?’ ” Thompson says.

Answering this second, crucial question requires locating birds in that predicted landscape. This is where all of Thompson’s previous research — how habitat fragmentation, predators, juvenile survival and other factors impacting survival rates — comes together.

“We bring in all of this information about nest survival, juvenile survival and environmental drivers together to try to predict whether in that landscape, the population would be increasing or decreasing,” Thompson says.

Not only does such modeling allow researchers to predict how birds might fare if things continue on their current trajectory, it also lets them evaluate what could happen when something not predicted occures.

“We can play ‘what if’ games,” Thompson says. “We can say, ‘What if severe storms increase due to climate change?’ Or ‘What happens if demand for wood products increases and timber harvest doubles in 100 years?’

“Or, for bird conservation, ‘What if, through landowner incentive programs, we encourage people to restore native grasslands?’ The state actually does that now. Or we ask, ‘What happens if we encourage landowners to manage their forests in a way that would benefit some of these species of concern?’ We can actually implement that in the model and predict how birds would respond.”

In fact, Thompson has used a landscape-based, population viability model to show that some of these conservation actions, when done on a big enough scale, could have real benefits for bird populations. That research was published in the journal Biological Conservation last year. The finding is one many conservationists will use, including Greg Wathen, coordinator for Gulf Coastal Plains & Ozarks Landscape Conservation Cooperative, part of a national network of applied conservation-science partnerships.

“Right now, we’re working with the Missouri Department of Conservation, the Arkansas Game and Fish Commission, the Oklahoma Department of Wildlife, and Frank’s lab to look at these future projections of forests [and to identify] what we’re calling conservation opportunity areas within that landscape — areas that would be important for conservation in the future,” Wathen says. “The work that Frank has been doing through these forest predictive models has been very important to us in terms of identifying those conservation opportunity areas.”

It’s exciting work, says Thompson. “Because we’re bringing all of these little things together now in a very comprehensive way, and that’s the way it happens in reality — those are all going on at once. In any particular study, we’ve got to pick them apart to understand them, but now we want to bring them back together.”

Post a Comment

Reader comments are reviewed by Illumination staff before they are posted, so please keep your message civil and appropriate. All fields are required.

– Will not be published

Back to Top

University of Missouri

Published by the Office of Research

© 2017 The Curators of the University of Missouri