Press Release: Despite Habitat Protection, Endangered Owls Decline in Mount Rainier National Park

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Spotted Owls in Mount Rainier National Park. Photo by Anna Mangan.

When the Northern Spotted Owl was protected under the Endangered Species Act in 1990, the primary threat to the species was the loss of the old-growth forest it depends on. However, new research published in The Condor: Ornithological Applications shows that the Northern Spotted Owl population in Washington’s Mount Rainier National Park has declined sharply in the past two decades despite the long-term preservation of habitat within the park. The culprit? The spread of Barred Owls, a closely related, competing species that has moved into Spotted Owls’ range from the east.

Biologists have seen Barred Owls in Spotted Owl territories within the national park more and more frequently since Spotted Owl surveys began in 1997. For their new study, Oregon Cooperative Fish and Wildlife Research Unit’s Anna Mangan, the National Park Service’s Tara Chestnut, and their colleagues analyzed two decades’ worth of data from these surveys. “We found that Spotted Owls now occupy 50% fewer territories in the park than they did 20 years ago when the study began, despite the lack of habitat disturbance,” says Chestnut. “Spotted Owls were less likely to be present in territories where Barred Owls were detected, and if Spotted Owls were there, sharing space with Barred Owls made them less likely to breed. Only 18 adult Spotted Owls were detected in the study area in 2016, down from a high of 30 owls in 1998.”

“Barred Owls eat a wider range of foods and use a greater variety of forested habitats, including the old-growth forest required by Spotted Owls, and these generalist traits have aided them in their highly successful range expansion throughout the Pacific Northwest,” explains co-author Katie Dugger, a researcher the US Geological Survey’s Oregon Cooperative Fish and Wildlife Research Unit. “Barred Owls are now competing with Northern Spotted Owls for food and space, and increased Barred Owl densities are associated with declines in Northern Spotted Owl populations across their range.”

“What is particularly alarming is that this decline has occurred even at Mount Rainier, where Spotted Owl habitat has been protected for over 100 years, with virtually no fire or logging disturbance,” says Mangan. “With Barred Owls detected at nearly every Spotted Owl territory monitored in the park, the future of Spotted Owls at Mount Rainier is tenuous. It also suggests that preserving owl habitat, while still crucial, is likely no longer enough to sustain the Spotted Owl population at Mount Rainier.”

If current trends continue, scientists predict that the Spotted Owl could be extinct in the region within approximately six to eight decades. “Conservation managers can focus on protecting old-growth habitat with steeper slopes, as we found this to have higher Spotted Owl occupancy, and can continue to monitor Barred Owl populations to better understand their effect on local Spotted Owl populations,” adds Mangan. “Managers will need to consider some creative solutions, and likely some unpopular choices, if the Northern Spotted Owl is going to be prevented from going extinct on public lands.”

Barred Owls reduce occupancy and breeding propensity of Northern Spotted Owl in a Washington old-growth forest is available at https://academic.oup.com/condor/article-lookup/doi/10.1093/condor/duz031.

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

Black-backed Woodpeckers & the Emerging Threat of Homogenous Forest Fires

Andrew Stillman

Linked paper: Nest site selection and nest survival of Black-backed Woodpeckers after wildfire by A.N. Stillman, R.B. Siegel, R.L. Wilkerson, M. Johnson, C.A. Howell, and M.W. Tingley, The Condor: Ornithological Applications.

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A Black-backed Woodpecker visits its nest in a burned tree. Photo by Jean Hall.

It’s fire season again in northern California. In some parts of the state, the evenings will glow with those too-familiar burnt orange sunsets while residents keep a wary eye on the news. Although wildfire can sometimes be catastrophic to human life and property, the raging flames don’t usually create lifeless wastelands. Walk through a recently burned forest, and you’ll be met with a myriad of birdsong. Fresh herbaceous growth and numerous wildflowers dot the forest floor, and woodboring beetles gnaw their way through burned trees. Then — if you’re lucky — you’ll hear it: the accelerating drum of the Black-backed Woodpecker.

Black-backed Woodpeckers are strongly associated with recently burned forests in the western U.S. They colonize these habitats rapidly after fire to take advantage of abundant post-fire resources, such as the dead trees that provide nest sites and access to a feast of woodboring beetle larvae. These birds may be jeopardized by logging activities that can destroy or degrade post-fire habitat, and Black-backed Woodpeckers are sometimes used as an indicator species to guide management activities on the post-fire landscape.

But post-fire landscapes are changing. Many recent studies indicate that current environmental conditions are yielding larger, more severe wildfires that leave post-fire habitat conditions outside of the historical norm. Add that to threats from post-fire logging, and we urgently need to understand how habitat specialists like the Black-backed Woodpecker will respond to these new conditions.

My colleagues from The Institute for Bird Populations and the U.S. Forest Service and I examined how Black-backed Woodpeckers use burned forest when deciding where to breed and whether the factors that influence nesting habitat selection also influence nest success. Over the course of eight years, we located 118 Black-backed Woodpecker nests in areas burned by six different fires, carefully monitoring the fate of each and surveying the characteristics of the surrounding habitat. Black-backed Woodpeckers selected moderately-sized nest trees in areas of high dead tree density burned at high severity. They also tended to select nest sites towards the outer edges of high burn severity patches. While our results showed strong relationships between nest site selection and habitat characteristics, we were surprised to find that none of the habitat variables that we measured affected nest success. Only nest initiation date had a strong effect, with early-season nests typically showing more success than late-season nests.

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Researchers take a break from collecting data in a patch of burned forest. Photo by Jean Hall.

We already knew that Black-backed Woodpeckers select nesting habitat with high densities of dead trees, but our results reveal an important nuance to this association with severely-burned forest. The birds in our study selected nest sites near the edges of severely burned patches — “ecotones” where the habitat transitions from severely-burned dead trees to intact living trees. The term for this is “pyrodiversity,” referring to the amount of variation in fire severity within an area and the different post-fire habitats that result. It seems that pyrodiversity is important for breeding Black-backed Woodpeckers. A related study, published recently in the Journal of Applied Ecology, found a similar positive association between pyrodiversity and the woodpeckers’ foraging habitat.

Changing fire regimes in the American West are leaving larger, more uniform areas of severely burned forest. This means less variation in post-fire landscapes, and potentially less habitat for pyrodiversity-loving species like the Black-backed Woodpecker. Our research suggests that land managers can manage burned forests to benefit Black-backed Woodpeckers by prioritizing retention of burned stands with dense dead trees located adjacent to areas burned at low severity or left unburned.

Reproduction Versus Immigration in North Carolina’s Piping Plovers

Chelsea Weithman

Linked paper: Growth of two Atlantic Coast Piping Plover populations by C.E. Weithman, S.G. Robinson, K.L. Hunt, J. Altman, H.A. Bellman, A.L. DeRose-Wilson, K.M. Walker, J.D. Fraser, S.M. Karpanty, and D.H. Catlin, The Condor: Ornithological Applications.

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An adult Piping Plover with a numbered leg bad. Photo by Katie Walker.

The beach: the sun, the sand, the water. It’s a wonderful place to be in the summer, whether you’re a shorebird or a human. Beach-nesting shorebird species increasingly have to share the shore with recreationists and human development, and many species of shorebird have been declining as a result. One beach-nesting specialist is the Piping Plover, which nests on sandy beaches along the North American Atlantic Coast, the Great Lakes, and riverine and alkali lakes of the Great Plains. To aid the recovery of the federally threatened Atlantic Coast Piping Plover, wildlife managers try to reduce disturbance and predation risks on its breeding grounds so that the plovers can successfully raise more fledglings. The hope is that increasing the number of fledglings will lead to population growth and, eventually, species recovery.

As part of my graduate work, my coauthors and I studied the population dynamics of Piping Plovers at Cape Hatteras National Seashore and other parts of the North Carolina Outer Banks. North Carolina is a particularly interesting place for these little shorebirds, because it hosts plovers throughout the year. Plovers have been studied in other parts of their range for decades, but the North Carolina population has not received as much attention. Would this breeding population be any different?

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Researchers survey a beach for Piping Plovers. Photo by Chelsea Weithman.

Based on analysis of long-term reported population estimates and reproductive output, this population—along with others in Virginia, Maryland, and Delaware—was thought to potentially reap some benefit from its position in the southern end of the breeding range. Particularly, these plovers were hypothesized to have higher survival rates, since they don’t have to migrate as far to reach their breeding ground as their brethren in the northeastern U.S. and Canada do. Perhaps, then, these southern populations may not need to produce as many young each year to maintain their population. If true, this difference in survival rates could have implications for how we think about and evaluate the recovery of this species. We set out to examine this hypothesis by comparing two populations in different areas of the breeding range: one population on Fire Island, New York, and one in North Carolina.

Contrary to our expectations, we found that plovers in North Carolina and New York have very similar survival rates and presumably need to produce similar numbers of chicks per breeding pair to maintain their populations. The New York population has grown considerably over the decades, especially after Hurricane Sandy created vast new areas of ideal habitat in 2012. The North Carolina population, on the other hand, has not met the estimated reproductive rate needed to maintain their population for more than 30 years. Based on this result, our burning question was, how are there still plovers in North Carolina at all?

We believe that the population in North Carolina is being sustained by a constant influx of immigrants—instead of chicks growing up and taking the place of their parents, immigrants from outside the population are keeping their numbers up. However, we don’t yet know where these immigrants are coming from or what their departure means for their original populations’ growth prospects. We’re continuing to study this phenomenon in hopes of better understanding how and why plovers choose to disperse and join other populations. This is important for the bigger picture of plover conservation, since so much time, energy, and money are dedicated to the important work of improving reproductive success. If other factors such as immigration are key components of a population’s health, then management strategies may need to be developed to support them, too.

Revisiting the Classics: What factors influence the start of the dawn chorus of House Wrens?

Sharon Gill, Erin Grabarczyk, and Maarten Vonhof

Linked paper: Social factors, not anthropogenic noise or artificial light, influence onset of dawn singing in a common songbird by C.J. Stuart, E.E. Grabarczyk, M.J. Vonhof, and S.A. Gill, The Auk: Ornithological Advances.

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A House Wren sings at its nest box. Photo by Erin Grabarczyk.

One of the daily joys of summer is waking to the sounds of bird song. Those early morning bursts of singing herald the start of our days, for birds and people alike. If we listen carefully, though, the dawn chorus also reveals something about the state of nature. We might channel Rachel Carson and, based on when birds start to sing each morning, consider what they are telling us about their environment.

What might birds tell us? Historically, they might have told us that cool temperatures on cloudy nights delayed the start of dawn singing. Or that female breeding partners were fertile and males were guarding them closely, either by singing more and earlier or singing less and later depending on the particular species. Today, birds might tell us about how they react to changes in their environment: do they sing earlier when the night sky is brighter, or later if it’s noisier at night, at dawn, or throughout the day?

It was the latter question that initially motivated us and led undergraduate Carley Stuart to do her honors thesis research on whether artificial light and human-caused noise affect the daily onset of the dawn chorus. But given the classic research that shows social context also modifies onset of singing, we considered the role of social factors such as the number of competitors or the mate’s fertility on the start of singing as well. We studied a common songbird, the House Wren, which breeds in nature preserves as well as urban environments. Our ongoing research on this species has found that males alter the structure of their songs and their responses to intruders under noisy conditions, but also that social context matters too. By considering anthropogenic influences and social context together, we hoped to get a broad perspective on the onset of the dawn chorus.

With these questions in mind, we headed to our field sites, positioning autonomous sound recorders at nest boxes to record the onset of singing by male House Wrens and ambient noise levels and using light meters to record sky brightness. We also color-banded and monitored the breeding activities of males, documenting their complex social lives.

We were glad we took this broader perspective. House Wrens began singing around civil twilight, when the sun was just starting to brighten the night sky. We found that it was social factors, not anthropogenic influences, that affected when males began to sing. More neighbours? Sing earlier. Nest building or fertile mate? Sing earlier. More noise and artificial light? Don’t change the timing of the dawn chorus. In regards to when males start their day, our research told us that House Wrens don’t appear to be bothered by artificial light and noise.

We were surprised by this result, as other species that begin dawn singing at similar times of day as House Wrens do sing earlier with brighter skies and more noise. Also, our previous studies have shown that noise affects male House Wrens in other ways, changing how they sing and how they interact with intruders. This makes our job of listening more complicated, as it means that just because one aspect of a bird’s life isn’t affected by human-generated environmental change doesn’t mean birds aren’t affected in other ways. That is a humbling prospect at this time of rapid environmental change and threats to our natural world. It means we need more information and broad assessments to fully understand the responses of animals to changing environments. We need to listen even more carefully.

https://birdsoundscapes.wixsite.com/gilllabwmu

Subsistence Harvest and Indigenous Knowledge in Alaska

Liliana Naves

Linked paper: Shorebird subsistence harvest and indigenous knowledge in Alaska: Informing harvest management and engaging users in shorebird conservation by L.C. Naves, J.M. Keating, T.L. Tibbitts, and D.R. Ruthrauff, The Condor: Ornithological Applications.

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Sharing a meal of wild foods with the James family at the community of Platinum, after an indigenous knowledge interview. Photo by Lili Naves, ADF&G Division of Subsistence.

Many shorebirds migrate across continents and oceans, relying on key areas to rest, eat, and refuel. Habitat loss, climate change, and other factors are affecting these birds at their breeding, migration, and wintering grounds. Numbers of long-distance migrating shorebirds that breed in North America are down by about 50% since the mid-1970s.

Biologists and social scientists joined forces in this interdisciplinary study to quantify shorebird harvest and document indigenous knowledge in Alaska. We wanted to learn about the importance of shorebirds as food and cultural resources, what Yup’ik people know about shorebirds, and how they could join in conservation efforts. We worked within the Harvest Assessment Program of the Alaska Migratory Bird Co-Management Council.

Twelve million shorebirds converge in Alaska every summer to breed, then migrate to winter in the Americas, the Pacific, and Asia. The Yukon-Kuskokwim delta in western Alaska provides critical habitat and food for these shorebirds. The delta is also the homeland of the indigenous Yup’ik people. For thousands of years, Yup’ik people have shared this vast wetland with shorebirds. Shorebirds represent only 1% of the subsistence bird harvest in Alaska, but this harvest includes species of conservation concern, in particular the Bar-tailed Godwit. These birds’ population size and adult survival have been declining, and some annual harvest estimates seemed high.

We generated Alaska-wide harvest estimates using a large dataset (775 community-years!) including surveys conducted between 1990 and 2015. The total harvest was about 2,800 shorebirds per year. Godwits were about 1,100 birds per year, and based on species distribution, these were all most likely Bar-tailed Godwits. The egg harvest was about 4,700 eggs per year.

The indigenous knowledge research for this study focused on the Yup’ik culture of the Yukon-Kuskokwim Delta. Working with tribal councils, we interviewed 80 respondents in 5 communities in 2017. We asked about shorebird ethnotaxonomy (how local people name birds and categorize species), importance for subsistence, place names, ecology, and concerns. Traditional knowledge is based on observation and experience accumulated over generations by people living in close contact with nature. We learned that shorebirds are known mostly by specialists. Yup’ik people name shorebirds in their Native language, so we worked with a translator. We learned 24 Yup’ik shorebird names, 7 of which were more widely known among our respondents. Most names are multi-species categories. Some names are onomatopoeic. For instance, the Yup’ik name for Wilson’s Snipe is Kukukuaq, after the sound made during their distinctive winnow display. Place names may tell about sites important for birds: Tevatevaaq Bay is a shallow, protected bay that indeed looks like a gathering place for the Tevatevaaq (Bar-tailed Godwit).

Shorebirds and their eggs are not primary food sources, but are harvested in times of scarcity. Traditionally, children learning to hunt focus on small birds, including shorebirds. Shorebirds are a joyful part of nature and connect people with their environment, traditional culture, and language. Yup’ik people have noticed a decline in local shorebird numbers in recent decades. Based on traditional knowledge, they understand that animals, people, and the land are interconnected. If populations of shorebirds or other animals are not doing well, something is out of balance in nature, and that thing may finally also affect people.

Whether a harvest is sustainable depends on both harvest levels and on the status of the bird populations being harvested. Data gaps still prevent robust assessments of shorebird harvest sustainability, but Bar-tailed Godwit populations currently have low harvest potential, and recent sharp declines in shorebird populations mean that we need to account for uncertainty in harvest sustainability in our conservation efforts. Shorebirds now depend on citizens, biologists, and managers to protect and restore their habitats. It is important to include indigenous peoples and other stakeholders in shorebird conservation along flyways. This study is already the basis for culture-focused conservation outreach efforts in western Alaska. As a next step, we want to collaboratively develop conservation approaches that benefit shorebirds as well as the well-being of these subsistence communities. We all play a role in our relationships with nature!