PRESS RELEASE: Study Reveals Key Locations for Declining Songbird

PROW_fullsize_Joan_Eckhardt
Many of North America’s Prothonotary Warblers winter in the same small area of Colombia. Photo by Joan Eckhardt.

Many of North America’s migratory songbirds, which undertake awe-inspiring journeys twice a year, are declining at alarming rates. For conservation efforts to succeed, wildlife managers need to know where they go and what challenges they face during their annual migration to Latin America and back. For a new study published by The Condor: Ornithological Applications, researchers in six states assembled an unprecedented effort to track where Prothonotary Warblers that breed across the eastern U.S. go in winter—their “migratory connectivity”—and found that nearly the entire species depends on a relatively small area in Colombia threatened by deforestation and sociopolitical changes.

The Ohio State University’s Christopher Tonra and his colleagues coordinated the deployment of 149 geolocators, tiny devices that use the timing of dawn and dusk to estimate birds’ locations, on Prothonotary Warblers captured at sites across their breeding range. When the birds returned to their nesting sites the following year, the researchers were able to recover 34 devices that contained enough data for them to use. The geolocator data showed that regardless of where they bred, most of the warblers used the same two major Central American stopover sites during their migration and spent the winter in a relatively small area of northern Colombia. Additionally, many Prothonotary Warblers appeared to winter in inland areas, rather than in coastal mangrove habitat, which previous studies suggested they relied on most heavily.

These unexpected findings show that we may not understand the winter habitat needs of migratory songbirds as well as we thought. “The most surprising thing about the results was the overwhelming importance of Colombia to this species,” says Tonra. “We weren’t sure what to expect in terms of migratory connectivity, but we never expected that nearly every bird would use the same wintering region. This provided a clear conservation message and shows the power of geolocators in addressing gaps in our knowledge of migratory songbirds.” Colombia’s 50-year civil war accelerated deforestation in the region of the country where the warblers are concentrated, but the good news is that the convergence of birds in this single area means that conservation efforts targeted here could benefit breeding populations across North America.

Collecting data on birds across such a broad geographic area required close collaboration among the study’s thirteen coauthors. “This was very much a team effort, but it really started with Erik Johnson at Audubon Louisiana and Jared Wolfe with the Louisiana Bird Observatory,” says Tonra. “Erik founded and leads our Prothonotary Warbler Working Group, and he initiated the idea of deploying tags across their range. This was an extremely rewarding example of what you can accomplish through collaboration across the range of a species of concern. Everyone put in an enormous effort to gather data in their region, as well as contributing to the preparation of the paper.”

Concentration of a widespread breeding population in few critically important nonbreeding areas: Migratory connectivity in Prothonotary Warbler is available at https://academic.oup.com/condor/article-lookup/doi/10.1093/condor/duz019.

About the journal: The Condor: Ornithological Applications is a peer-reviewed, international journal of ornithology, published by the American Ornithological Society. For the past two years, The Condor has had the number one impact factor among 27 ornithology journals.

PRESS RELEASE: UV Lights on Power Lines May Help Save Sandhill Cranes

Illuminating power lines with UV lights could reduce collisions by Sandhill Cranes. Photo by James Dwyer, EDM International.

Crane species are declining around the world, and lethal collisions with power lines are an ongoing threat to many crane populations. Current techniques for marking power lines and making them more visible to cranes aren’t always effective, but new research published in The Condor: Ornithological Applications shows that adding UV lights—to which many birds are sensitive—can cut crane collisions with power lines by 98%.

EDM International’s James Dwyer and his colleagues created what they dubbed the Avian Collision Avoidance System, or ACAS, by mounting UV lights on power lines’ supporting structures and shining them on the lines at night. They tested its effectiveness in 2018 at Nebraska’s Iain Nicolson Audubon Center, where a power line crosses the Central Platte River in key habitat for migrating Sandhill Cranes. Randomly assigning the ACAS to be on or off each night, they observed the behavior of cranes flying along the river at dusk and during the night. They documented 98% fewer collisions and 82% fewer dangerous flights when the ACAS was on and showed that cranes reacted sooner and with more control to avoid hitting the power lines.

“This project came about as a result of years of studying avian collisions with power lines throughout North America. My studies included collisions involving numerous species and families of birds, even on lines modified to industry standards to mitigate avian collisions, and I thought perhaps there could be a more effective approach,” says Dwyer. “Even so, I did not imagine that the ACAS would have the effect that it did—a 98% reduction in collisions! I thought it would have some effect, but I didn’t dare think the ACAS would pretty much solve the Sandhill Crane collision problem at our study site on our first try.”

The Avian Collision Avoidance System at night. Photo by James Dwyer, EDM International.

Conventional line markers were already in place on the power lines crossing the Central Platte River, and Dwyer and his colleagues speculate that the ACAS illuminated them and made them easier for cranes to see. “We don’t know how effective the ACAS will be on wires without line markers, so we’re testing that now,” says Dwyer.

“I hope to see the ACAS applied to and studied on other power lines and on communication towers to identify whether it is as effective with other species, habitats, and wire configurations,” he continues. “From there, if the ACAS proves broadly effective, I hope to see it made easily available to the global electric industry. I also very much hope to see collision studies expanded. Because large carcasses like those of cranes and waterbirds are more easily noticed than smaller species like sparrows and warblers, collision studies have mostly focused on those larger species, and I fear that we may not understand the true distribution of species and habitats involved in the global avian collision problem.”

Near-ultraviolet light reduced Sandhill Crane collisions with a power line by 98% is available at https://academic.oup.com/condor/article-lookup/doi/10.1093/condor/duz008.

About the journal: The Condor: Ornithological Applications is a peer-reviewed, international journal of ornithology, published by the American Ornithological Society. For the past two years, The Condor has had the number one impact factor among 27 ornithology journals.

Singing Above the Urban Ruckus, If You’re a Mockingbird

Mitchell Walters

Linked paper: Urban background noise affects breeding song frequency and syllable-type composition in the Northern Mockingbird by M.J. Walters, R.P. Guralnick, N.J. Kleist, and S.K. Robinson, The Condor: Ornithological Applications.

Northern Mockingbirds adjust their songs to noisy urban environments. Photo by Mitchell Walters.

Imagine having a conversation with someone next to a very busy intersection at rush hour. You can’t hear one another at a normal volume, so what do you do? You could talk louder, maybe wait for the noise to die down, or simply pick up your belongings and move to a quieter setting to converse.

Our research shows that if you’re a Northern Mockingbird, one of North America’s most famous avian songsters and the state bird of five U.S. states, you adjust to noisy settings by conversing at a higher pitch. Northern Mockingbirds’ songs are incredibly complex, made up of hundreds of different elements, and we also found that urban mockingbird songs include more high-pitched elements.

So why raise your pitch? Noise in urban environments overlaps most strongly with lower-frequency bird vocalizations, so mockingbirds may be increasing the pitch of their songs to avoid being drowned out by urban background noise. However, mockingbirds also love to mock things, so it’s possible that individuals mimic higher-pitched sounds more often in urban environments. In any case, the Northern Mockingbird is a great example of a bird adapting to urban habitat. Previous research in our lab has shown that not only is this species more abundant in urban areas, it also adjusts its nesting, foraging, and anti-predator behavior in these settings. The acoustic flexibility we found in our study may add to their ability to coexist with urbanization and people.

Because mockingbirds love to mock other bird species in their environment, it also makes sense to ask how much of a role surrounding bird communities play in the characteristics of their songs. This is important, because a male who’s a prolific impressionist may be very attractive to female mockingbirds. Future research aims to look at whether urbanization affects the quality of mockingbird songs via changes in bird diversity. If this is true, then human disturbance could be indirectly impacting the evolutionary trajectory not only of Northern Mockingbirds, but of other mimicking species as well.

When I started my master’s degree at the University of Florida, I actually had no intention of working with mockingbirds. I originally planned to do a project overseas, but my advisor and I quickly realized that was unrealistic. After a few mild panic attacks and brainstorming sessions I turned to urban ecology, a topic I had recently developed an interest in. Our lab had done long-term studies on urban mockingbirds, but no one had looked at what was, in my opinion, the most fascinating part of mockingbird life history — their songs. So the stage was set, the field gadgets were bought, and the grant proposals were accepted, sort of. After two years of blistering Florida summer heat and several strange encounters with locals asking what the heck I was doing with recording equipment, the project was complete and the results are now in! I just want to thank AOS for publishing my first first-author manuscript; it’s been an absolute pleasure working with this amazing journal.

AUTHOR BLOG: Lifting hunting limits hasn’t solved the Snow Goose overpopulation problem

Robert Rockwell

Linked paper: Liberalized harvest regulations have not affected overabundant Snow Geese in Northern Manitoba by D.N. Koons, L.M. Aubry, and R.F. Rockwell, The Condor: Ornithological Applications.


A large flock of snow geese during spring migration in North Dakota. Photo by Craig Bihrle, North Dakota Game and Fish Department.

As many marshes along the Gulf Coast were drained in the late 1970s, Snow Geese that had used them as wintering areas began shifting to agricultural land instead. Leftover crops in farm fields provided them with a generous new winter and spring diet, and the population began growing at an unprecedented rate. While they have ample habitat in the south, the growing number of geese, coupled with their destructive foraging behaviors, has led to increasing and widespread habitat destruction in the Arctic coastal habitats where they breed.

In response to this habitat degradation and the resulting negative impacts on other species, the U.S. and Canada attempted to reduce the size of the population by liberalizing the regulations on Snow Goose hunting beginning in 1997. This included increasing bag and possession limits, expanding the hours during which hunting is permitted, allowing the use of unplugged shotguns and electronic callers, and instituting a spring conservation harvest. Adult mortality has a greater relative impact on the growth rate of this species than any other demographic variable, so wildlife managers hoped that removing more adults from the population through hunting would help bring it under control.

Severely degraded coastal and near-coastal habitat in Wapusk National Park outside of Churchill, Manitoba, Canada. Photo by Stephen Brenner, Nebraska Game and Parks Commission.

Adaptive Harvest Management is an approach used in North America that examines the impacts of management decisions and readjusts those decisions as necessary to meet management goals. We used our 50-year database on more than 100,000 Snow Geese banded on Canada’s Cape Churchill Peninsula to assess whether the new regulations were having the desired effect of increasing adult mortality. Using new analytical techniques, we could estimate the rates of both hunter and non-hunter deaths of adult geese and see whether those rates changed when the new hunting regulations were implemented.

Adult harvest mortality has stabilized at a low level, with only around 3% of adult geese being killed by hunters in a given year, probably because the sheer abundance of Snow Geese in this population has overwhelmed the number of hunters. The number of North American hunters has not increased in recent years, and most hunters are only willing to harvest enough geese to meet their family’s needs. Adult non-harvest mortality declined through the 1970s and 1980s to trivial levels (around 1% per year), but has increased recently and now fluctuates between 10% and 19% per year. Unfortunately, the combined mortality isn’t enough to limit the species’ growth, and the population continues to increase in size.

In light of our results, the next cycle of Adaptive Harvest Management needs to consider the potential causes of the increase in non-hunting mortality and its year to year variability, especially since such variation actually reduces overall population growth rate. We also suggest that management agencies further refine hunting regulations to increase the harvest per hunter and make efforts to increase public participation in hunting, perhaps through outreach to currently underrepresented groups.

The authors are all associated with the Hudson Bay Project. More about our work can be found at http://research.amnh.org/users/rfr/hbp.

AUTHOR BLOG: Herbicides Don’t Affect Survival of White-Crowned Sparrow Nests & Fledglings

Jim Rivers

Linked paper: No evidence of a demographic response to experimental herbicide treatments by the White-crowned Sparrow, an early successional forest songbird by J.W. Rivers, J. Verschuyl, C.J. Schwarz, A.J. Kroll, and M.G. Betts, The Condor: Ornithological Applications.

A juvenile White-crowned Sparrow. Photo by Jim Rivers.

A number of birds that use forests disturbed by timber harvest have been declining for decades in North America’s Pacific Northwest. In this region, timber management often requires spraying competing vegetation with herbicides so that crop trees can grow, but the consequences of this herbicide treatment on bird nesting are poorly understood. We designed an experiment to find out how herbicide application was affecting nesting in the White-crowned Sparrow, a songbird that’s declining in the Pacific Northwest. We treated study sites with different levels of herbicides, as well as establishing control sites that experienced no herbicide application. Then, we located and monitored sparrow nests at each site to evaluate how herbicide intensity influenced the outcomes of nesting attempts and the survival of fledgling birds immediately after leaving the nest.

Although herbicide treatments had a major effect on the vegetation in our study plots, as we had expected, we found no effect of herbicide treatment on nest survival. That is, nests had similar rates of survival regardless of where they were located across the continuum of herbicide intensity. Similarly, the survival of fledgling sparrows did not differ between control sites that received no herbicide and sites where herbicide was applied in a way that simulated current management of industrial forest plantations. These results were surprising, because we know from previous work that herbicides have a strong influence on the extent of broadleaf vegetation, a key habitat component for foraging and nesting for many declining songbirds including the White-crowned Sparrow.

White-crowned Sparrow nest with eggs. Photo by Jim Rivers.

Although our study demonstrated that herbicides reduced plant cover in the general area around sparrow nests, we did find that the amount of concealment provided by nest site vegetation was similar across treatments. This suggests that despite the reduction in vegetation cover from herbicides, sparrows in even the most intensively-treated stands were still able to find suitable hiding places for their nests. Because most nest failures were due to predators, it’s possible that nest predators were impacted more by vegetation cover right around the nests than by a reduction in vegetation cover at bigger scales. We were unable to measure predators in our study, but hopefully future work in this system can improve our understanding of the ecology of songbird nest predators and how they are—or are not—affected by herbicide treatments.

Many declining bird species in the Pacific Northwest are united by their need for recently-disturbed forests that contain broadleaf vegetation. Our work shows that one declining species, the White-crowned Sparrow, is not influenced by herbicide intensity, but it remains unknown whether these results also apply to other species. Therefore, studies that expand beyond sparrows would be especially useful for understanding the effects of herbicides on other species that have similar habitat requirements yet differ in their foraging behaviors.

Learn more about the work of the Forest Animal Ecology Lab by visiting their website or following them on Twitter.