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.

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!

Tracking Guam’s snake survivors

Henry Pollock

Linked paper: Pervasive impacts of invasive brown treesnakes drive low fledgling survival in endangered Micronesian Starlings (Aplonis opaca) on Guam by H.S. Pollock, J.A. Savidge, M. Kastner, T.F. Seibert, and T.M. Jones, The Condor: Ornithological Applications.

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A Micronesian Starling. Photo by Martin Kastner.

For bird aficionados, waking up on Guam can be a surreal experience. The soundscape is nearly devoid of birdsong other than the clucking of chickens and the occasional chirp of a Eurasian Tree Sparrow. Guam’s silent forests are the work of the brown treesnake, an invasive predator that was accidentally introduced to the island after World War II. Following its initial establishment on Guam, the brown treesnake population exploded, causing the extirpation of ten out of the island’s twelve native forest bird species within a few decades. However, a couple of species have managed to persist, and understanding how they’ve managed this feat in the face of such a formidable predator can inform future avian conservation strategies and snake suppression efforts on Guam.

Our research focused on the Micronesian Starling or Sali, a glossy black, gregarious bird that is a staple of forests throughout the Mariana Islands. On Guam, Sali declined precipitously following the introduction of the brown treesnake, but a small population has managed to persist in an urbanized landscape on Andersen Air Force Base in northern Guam. To understand why Sali have survived while so many other bird species have disappeared, we set out to study fledgling survival. The post-fledging period, when a bird has left its nest but is still dependent on its parents, is a period of great vulnerability, because young birds are often clumsy, sedentary, and less equipped to evade predators than adults.

To track fledglings through this crucial period, we attached small radio transmitters to Sali just before they left the nest and then came back each day to see whether our birds had survived the previous night and where they were spending their time. All of our birds fledged from nest boxes in an urban housing area, and tracking young birds through backyards on a military base was an interesting experience. We had regular run-ins with the military security forces, as well as also a lot of curious homeowners wondering what exactly we were doing decked out in field gear and holding large antennas! After a while, though, people got to know us, and many were truly interested in what we were doing and excited to know that they had a locally endangered bird species in their own neighborhood.

Our findings were staggering: only 25% of the fledglings survived, one of the lowest fledgling survival rates ever recorded for any bird species. The primary culprit was, of course, the brown treesnake, which caused approximately 60% of all mortality. However, cats were also an important source of mortality, responsible for around 20% of fledgling deaths. Beyond establishing these baseline numbers, however, we were also able to identify spatial patterns of predation risk and provide important management recommendations for future bird conservation on Guam.

We found that fledglings from nest boxes closer to the forest were more likely to be killed by brown treesnakes, indicating that locating nest boxes in core urban areas away from the forest perimeter would maximize fledgling survival. Furthermore, our data showed that brown treesnake predation actually extended weeks beyond the vulnerable post-fledging period, demonstrating again that these snakes are uniquely pernicious predators and that intensified snake control efforts are needed. We hope that our research provides impetus for further controlling the invasive brown treesnake and serves as a stepping stone for bringing birds back to Guam and enriching the island’s soundscape once again.