AUTHOR BLOG: How vulnerable are California’s Great Gray Owls to wildfire?

Rodney Siegel

Linked paper: Short-term resilience of Great Gray Owls to a megafire in California, USA by R.B. Siegel, S.A. Eyes, M.W. Tingley, J.X. Wu, S.L. Stock, J.R. Medley, R.S. Kalinowski, A. Casas, M. Lima-Baumbach, and A.C. Rich, The Condor: Ornithological Applications 121:1, February 2019.

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A Great Gray Owl nest within an area recently burned by the 2013 Rim Fire in Yosemite National Park. Photo credit: Dustin Garrison

Throughout western North America, the combination of longer, hotter dry seasons and dense forests is yielding more frequent, larger, and more severe wildfires, including immense “megafires.” Habitat loss from increased fire activity could put wildlife species that depend on mature forest at risk. Concern over this threat is an increasingly important driver of forest management efforts in California’s Sierra Nevada, but recent efforts to assess the consequences of megafires on one bird species associated with the region’s mature forest, the California Spotted Owl (Strix occidentalis), have yielded conflicting results. Some research suggests that California Spotted Owls may be vulnerable to habitat loss and local extirpation due to forest fire, while other studies indicate that the owls may be fairly resilient, at least to low- and mixed-severity fire.

Like Spotted Owls, the Great Gray Owl (Strix nebulosa) is imperiled in California (where it is listed by the state as endangered) and is associated with mature forest. California’s Great Gray Owls typically nest in large, dead trees in shady forests adjacent to mountain meadows. In 2013 the Rim Fire, the largest fire on record in the Sierra Nevada, burned 104,000 hectares in Yosemite National Park and Stanislaus National Forest – the heart of Great Gray Owl’s range in California. Within the burned area were 23 meadows known to be occupied by Great Gray Owls during the decade prior to the fire, nearly a quarter of all known or suspected territories in California at the time.

We analyzed 13 years (2004–2016) of Great Gray Owl survey data from 144 meadows in the central Sierra Nevada, including meadows inside and outside the Rim Fire perimeter in Yosemite National Park and Stanislaus National Forest, to assess the effect of the fire on Great Gray Owls’ persistence during the early post-fire years. Would Great Gray Owls continue to use historically occupied meadows within the burned area, or would the fire cause those sites to go vacant?

During three years of surveys after the fire, we detected Great Gray Owls at nearly all (21 of 22) surveyed meadows within the burned area that were occupied during the decade prior to the fire, and anecdotal evidence indicated that the owls were not only present but actually nested at many of these sites during the post-fire years. Analyzing the full dataset, including surveys conducted before and after the fire as well as inside and outside the burned area, revealed that rather than decreasing after the fire, owls’ persistence actually increased at meadows across the study area. This increase suggests that the owls remained resilient during the three years after the Rim Fire and that other factors such as weather were likely favorable to Great Gray Owls during those post-fire years.

Our results indicate that wildfires, including unusually large megafires, may not pose a great threat to Great Gray Owls in the short term. However, processes not apparent during our study’s short timeframe, including the eventual decay and loss of the large snags that the fire created, could affect the owls’ longer-term persistence after fire. Further study is needed to determine whether Great Gray Owls continue to be resilient to fire over longer timeframes.

More information about The Institute for Bird Populations’ Great Gray Owl research and conservation efforts is available at http://birdpop.org/pages/greatGrayOwlResearch.php.

Road Proximity May Boost Songbird Nest Success in Tropics

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A juvenile White-rumped Shama with identifying leg bands. Photo credit: Rongrong Angkaew

In the world’s temperate regions, proximity to roads usually reduces the reproductive success of birds, thanks to predators that gravitate toward habitat edges. However, the factors affecting bird nest success are much less studied in the tropics—so does this pattern hold true? New research published in The Condor: Ornithological Applications shows that interactions between roads, nesting birds, and their predators may unfold differently in Southeast Asia.

Rongrong Angkaew of King Mongkut’s University of Technology Thonburi and her colleagues placed 100 next boxes for the cavity-nesting White-rumped Shama in forest interior and 100 near a road at an environmental research station in northeast Thailand. Monitoring nests and radio-tracking 25 fledglings from each site for seven weeks, they found that nest success was 12% higher and post-fledging survival 24% higher at the edge versus the interior—the opposite of the pattern commonly observed in temperate regions.

“There were some special challenges involved in carrying out the field work,” says Angkaew. “When we started setting up the nest boxes in the field, we found a lot of tracks and other signs of poachers and illegal hunting, so we had to avoid some parts of the forest edge in order to reduce human disturbance to our nest boxes, which could have affected nestling and fledgling survival rates.”

Predators caused 94% of nest failures and 100% of fledgling mortality, and locally important predators of small birds, such as green cat snakes, northern pig-tailed macaques, and raptors, appear to prefer interior forest habitat. Fledglings also preferred to spend time in dense understory habitat, which provides cover from predators and was more available near roads.

Overall, the study’s results suggest that the effects of roads on birds’ reproductive success depend on local predator ecology—the same rules don’t necessarily apply in different biomes. Angkaew and her coauthors hope that more studies like theirs will help identify key nest predators and assess their foraging behaviors in multiple landscapes, in order to determine the best ways to conserve vulnerable bird species in areas affected by human development.

Nesting near road edges improves nest success and post-fledging survival of White-rumped Shamas (Copsychus malabaricus) in northeastern Thailand is available at https://academic.oup.com/condor/article/121/1/duy013/5303795.

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.

Homebody Tendencies Put Hawaiian Gallinules at Risk

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Hawaiian Gallinules’ limited dispersal may be putting them at risk. Photo credit: J. Underwood

The Hawaiian Islands are home to a range of unique, endangered bird species. Many waterbirds such as the Hawaiian Coot and Hawaiian Gallinule have been recovering in recent decades thanks to intensive wetland management, but past declines have left them with reduced genetic diversity. A new study from The Condor: Ornithological Applications looks at what the birds’ genes can tell us about their behavior today and finds that one species’ lack of wanderlust may be putting it at greater risk.

The U.S. Fish and Wildlife’s Jared Underwood and his colleagues trapped birds on Oahu and Kauai and took blood, tissue, and feather samples. Genetic analysis conducted at the U.S. Geological Survey by Sarah Sonsthagen and colleagues showed that Hawaiian Coots disperse regularly between islands, while Hawaiian Gallinules do not. The researchers believe that Hawaiian coot populations in some wetlands are reaching the maximum they can support, which is one factor causing them to leave in search of new territories. Historical evidence suggests that gallinules also moved around frequently prior to population declines, so either their behavior has changed, or, unlike the coots, they have yet to reach local carrying capacities.

“The Common Gallinule as a species is considered quite vagile—that is, it tends to move around a lot—so it was surprising to find a high level of genetic structure between two islands separated by only 175 kilometers,” says coauthor Jared Underwood. “Other Common Gallinule subspecies found in the Pacific frequently move between islands that are separated by greater distances.” Hawaiian Gallinules’ homebody tendencies put them at greater risk from severe one-off events like hurricanes, which could wipe out an entire island’s worth of birds. Their lack of gene flow also means that populations on individual islands need to be larger in order to be viable long-term.

Despite recent population gains, the researchers warn that rising seas, diseases, and introduced predators continue to threaten both species. “A key component of the resilience and persistence of species and populations is the retention of genetic diversity,” adds Underwood. “Information regarding the genetic structure for each species will allow managers to design different strategies and criteria for the species’ recovery.”

Interisland genetic structure of two endangered Hawaiian waterbirds: The Hawaiian Coot and Hawaiian Gallinule is available at http://americanornithologypubs.org/doi/full/10.1650/CONDOR-18-98.1.

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.

AUTHOR BLOG: Saving Saltmarsh Sparrows will help other species, too

Chris Elphick

Linked paper: Evaluating a focal-species approach for tidal marsh bird conservation in the northeastern United States by B.T. Klingbeil, J.B. Cohen, M.D. Correll, C.R. Field, T.P. Hodgman, A.I. Kovach, B.J. Olsen, W.G. Shriver, W.A. Wiest, and C.S. Elphick, The Condor: Ornithological Applications 120:4, November 2018.

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Salt marshes in the northeastern USA are getting wetter, increasing the risk that the nests of marsh-breeding birds will be flooded during high tides. Photo credit: Chris Elphick

Saltmarsh Sparrows are in trouble. They are found only in the eastern USA and—as their name suggests—occur only in salt marshes, nesting primarily in the higher elevation portions that are dominated by saltmeadow cordgrass (Spartina patens) and where the risk of nests flooding is lowest. With rising sea levels and increasing storm surges, however, that risk is rising. Since the 1990s, the global population of Saltmarsh Sparrows has declined by about 75%, and demographic studies suggest that extinction is likely by mid-century. Marshes are also changing, with a shift towards vegetation characteristic of wetter conditions, supporting the idea that sea level rise is responsible and that flooding risk for the birds is increasing.

The good news is that people are starting to take notice. The species is considered globally endangered by BirdLife International, it is being assessed for listing under the US Endangered Species Act (ESA), and it is the subject of considerable attention by the Atlantic Coast Joint Venture, which represents most of the key management agencies in states where the species occurs.

Saltmarsh Sparrows, of course, are not the only birds that use salt marshes in eastern North America. Black Rails have already disappeared from much of the East and were recently proposed for ESA listing; Clapper Rails and Nelson’s Sparrows are also declining in the northeastern USA, the only region for which there are comprehensive, large-scale surveys; and other salt marsh specialists nest in similar conditions and will potentially face a similar fate in coming decades.

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Conservation for Saltmarsh Sparrows (right) is likely to benefit most other salt marsh specialist birds nesting in the northeastern USA. An exception is Nelson’s Sparrow (left), which has limited range overlap and will require separate conservation actions. Photo credit: Chris Elphick

A key question, then, is whether conservation focused on Saltmarsh Sparrows will also benefit these other species. Conservation biologists have long debated the pros and cons of management focused on individual species. Arguably, centering conservation on an individual species can help garner conservation support that will have ecosystem-wide benefits. At the same time, if the chosen species does not adequately represent the entire suite of species (or other ecosystem properties) that one wants to protect, then the endeavor will fail. In our new paper, we set out to test whether Saltmarsh Sparrows can play this role.

Using the conservation planning software MARXAN, we prioritized salt marsh patches for five bird species that nest in salt marshes across the ten states in which Saltmarsh Sparrows breed.  These species are those most dependent on salt marshes and most likely to be affected by changes to the habitat. (Black Rail, the sixth species in this group, is now so rare in these states that it was not included.) We found that land protection scenarios focused on Saltmarsh Sparrows are more effective at protecting the entire suite of species than scenarios focused on any of the other individual species. Conserving areas that support the bulk of the current Saltmarsh Sparrow population will also protect large (>50,000) populations of all other species except Nelson’s Sparrow. Similar planning based on Clapper Rails—the other declining species—performed much worse, while multispecies combinations performed no better. Nelson’s Sparrow would not be protected well by prioritizing based on any of the proxy species considered, which is not surprising, given the limited overlap between the range of this species and the other four.

Of course, showing that conservation focused on Saltmarsh Sparrows will benefit other salt marsh specialist birds is only a partial answer to the question of whether they are a good focal species for long-term conservation of salt marshes. Birds that use these marshes outside the breeding season, other types of organisms, and the full range of other ecosystem services that marshes provide also warrant consideration. It is clear, however, that work designed to protect sparrows has good potential to benefit some of the other high-priority conservation targets. And given the reliance of Saltmarsh Sparrows on high-elevation marsh—the portion of the system that seems to be most vulnerable to losses due to sea level rise—it appears likely that other organisms that use this habitat will also benefit.

Getting to the Root of Long-Term Tree Swallow Declines

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Kent Island’s Tree Swallow population has collapsed as immigration from the mainland has declined. Photo credit: B. Woodworth

Aerial insectivores—birds that hunt for insect prey on the wing—are declining across North America. Conserving vulnerable species such as these requires a good understanding of the factors impacting them at every stage of life. Juveniles and adults, for example, may face different threats and die at different rates. Two new studies from The Condor: Ornithological Applications take a deep dive into the demographic factors behind declining populations of Tree Swallows and show that although specifics may vary between locations, action is needed to address environmental changes affecting these birds across their geographic range.

Queen’s University’s Amelia Cox and her colleagues used a dataset from a swallow population in southeastern Ontario that was monitored from 1975 to 2017, while Bowdoin College’s Liam Taylor and his colleagues looked at data from a population from an island off the coast of New Brunswick that was monitored from 1987 to 2010. Having access to detailed long-term data allowed both sets of researchers to do demographic analysis and determine which life stages were having the largest impact on local population declines. In Ontario, overall declines were driven primarily by drops in overwinter survival and the rate at which swallow chicks successfully left the nest. On Kent Island, analysis showed that the population was dependent on immigration from the mainland, which dropped as mainland populations declined throughout the region. Over the course of the study, the Kent Island population plummeted from 202 adult birds to only 12.

Cox and her colleagues believe that increasingly unfavorable weather conditions and declines in insect availability may be behind the demographic shifts they found. “I hope that our results will spur more research into the environmental causes of Tree Swallow declines and declines of other similar species. Our research points the finger at poor survival overwinter and poor fledging as the probable demographic causes of population declines,” says Cox. “The next step is to figure out exactly what has changed in their environment and why these birds are dying during these critical life stages. We have additional work in progress that is aimed at answering these questions. When we know that, I hope we will be able to start making changes to improve survival and fledging.”

“It was an incredible opportunity to analyze a dataset that started before I was born,” adds Taylor. “Working with these long-term data had an emotional connection for me as a researcher and birder. My own fieldwork on Kent Island took place during the summers of 2014 and 2015, by which time most of the swallow nest boxes on the island were empty. For me, it was sobering to look back through the data and envision those nest boxes full of activity and life.”

“These studies are part of a growing number of studies addressing the causes of population declines among aerial insectivores,” according to the University of Wisconsin-Milwaukee’s Peter Dunn, a Tree Swallow expert who was not involved in either project. “In terms of understanding population declines in aerial insectivores, both studies point to adult survival during migration or on wintering areas as an important factor. Thus, these models identify areas where we can focus our future research efforts. Recent studies of Tree Swallow migration using geolocators suggest that populations breeding in eastern Canada are migrating along the east coast to winter primarily in Florida and Cuba, so these areas should probably be the next focus of study.”

Demographic drivers of collapse in an island population of Tree Swallows and Demographic drivers of local population decline in Tree Swallows (Tachycineta bicolor) in Ontario, Canada are available at http://americanornithologypubs.org/doi/full/10.1650/CONDOR-18-75.1 and http://americanornithologypubs.org/doi/full/10.1650/CONDOR-18-42.1.

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.