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.

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.

Newly Discovered Hummingbird Species Already Critically Endangered

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A male Blue-throated Hillstar. Photo credit: F. Sornoza-Molina

In 2017, researchers working in the Ecuadorian Andes stumbled across a previously unknown species of hummingbird—but as documented in a new study published in The Auk: Ornithological Advances, its small range, specialized habitat, and threats from human activity mean the newly described Blue-throated Hillstar is likely already critically endangered.

Hillstars are unusual among hummingbirds—they live in high-elevation habitats in the Andes and have special adaptations to cold temperatures. Francisco Sornoza-Molina of Ecuador’s Instituto Nacional de Biodiversida, first observed and photographed a previously unknown hillstar during fieldwork in southwest Ecuador in April 2017. After this first expedition, Sornoza-Molina engaged fellow researchers Juan Freile, Elisa Bonaccorso, Jonas Nilsson, and Niels Krabbe in the study of this possible new species, returning in May to capture specimens and confirm the finding. They dubbed the new species Oreotrochilus cyanolaemus, or the Blue-throated Hillstar, for its iridescent blue throat.

The Blue-throated Hillstar is found only along bush-lined creeks in an area of about 100 square kilometers, and the researchers estimate there are no more than 750 individuals, perhaps fewer than 500. Threats to its habitat include fire, grazing, and gold mining, and it meets the criteria to be considered critically endangered. “Complete support from national and international conservation agencies is needed in order to save this species,” says coauthor Francisco Sornoza-Molina. “The action plan for the conservation of this bird is creating a network of protected areas along its geographic range.”

“The hillstar hummingbirds occur in the most rugged, isolated, and inaccessible parts of the Andes, where they roost in caves, forage on the ground, and spend half their lives in hypothermic torpor, so the discovery of a new species in this group is incredibly exciting. This striking discovery confirms that life in the high Andes still holds many secrets to be revealed,” according to the University of New Mexico’s Christopher Witt, a hummingbird expert who wasn’t involved in the study. “The location is fitting for a new species of hillstar, because it’s a remote, high mountain range that is isolated and is sandwiched between the ranges of two other hillstar species. The authors did a thorough job comparing the new form to its relatives in every respect.”

A striking, critically endangered, new species of hillstar (Trochilidae: Oreotrochilus) from the southwestern Andes of Ecuador is available at http://americanornithologypubs.org/doi/full/10.1642/AUK-18-58.1.

About the journal: The Auk: Ornithological Advances is a peer-reviewed, international journal of ornithology published by the American Ornithological Society. The Auk commenced publication in 1884 and in 2009 was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.

Improving “Silvopastures” for Bird Conservation

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Black-crowned Antshrikes are among the insectivorous birds that forage less efficiently in silvopasture habitat. Photo credit: B. Tarbox

The adoption of “silvopastures”—incorporating trees into pastureland—can provide habitat for forest bird species and improve connectivity in landscapes fragmented by agriculture. But how do silvopastures measure up to natural forest habitat? New research from The Condor: Ornithological Applications shows that birds in silvopasture forage less efficiently than those in forest fragments but offers suggestions for how silvopasture habitat could be improved.

The University of Florida’s Bryan Tarbox and his colleagues observed the foraging and flocking behavior of insect-eating birds in silvopastures on farms in the Colombian Andes between 2013 and 2015. They found that silvopastures were less structurally complex than forest fragments, with fewer and smaller trees, a sparser understory, and less diversity of tree species. Birds in silvopastures attacked insects less often, were less selective about where they foraged, and were less likely to join mixed-species flocks. Flock members attacked prey more frequently than solitary birds in forest fragments, but not in silvopastures, suggesting that something about silvopasture habitat negated the benefits of joining a flock.

The results show that silvopasture habitat could be improved by managing for higher tree species diversity and greater structural complexity, but that preserving natural forest fragments in agricultural landscapes is also crucial. “I hope people don’t get the impression that our results mean silvopastures aren’t a good idea,” says Tarbox. “The existing literature makes it clear that silvopastures are beneficial for biodiversity conservation. I think the big takeaway here is the importance of getting to the details of how specific land uses impact particular species or functional groups, so that we can figure out the best regional configurations of land use, given the competing needs of wildlife and agriculture.”

“Protected areas alone will be insufficient to conserve biodiversity at global scales. Instead, we must find ways to safeguard species and ecosystems while also sustaining human communities and livelihoods that depend upon local resources,” according to Cornell University’s Amanda Rodewald, an expert on bird responses to human land use who was not involved with the research. “In their study of insectivorous forest birds, Tarbox and his colleagues report that Andean silvopastures provided low quality foraging habitats and, as such, may fail to support resident and migratory birds as well as forest fragments. Fortunately, the study points to several strategies, such as planting preferred tree species and creating specialized microhabitats, that can be implemented at local and regional scales to improve suitability of silvopastoral habitats for birds.”

Foraging ecology and flocking behavior of insectivorous forest birds inform management of Andean silvopastures for conservation is available at http://americanornithologypubs.org/doi/full/10.1650/CONDOR-18-1.1.

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.

Newly Identified African Bird Species Already in Trouble

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A Mountain Sooty Boubou. Photo credit: J. Engel

Central Africa’s Albertine Rift region is a biodiversity hotspot consisting of a system of highlands that spans six countries. Recent studies have shown that the population of sooty bush-shrikes occupying the region’s mid-elevation forests is a distinct species, and new research from The Condor: Ornithological Applications reveals that this newly discovered species may already be endangered due to pressure from agricultural development.

The newly identified mid-elevation species has been dubbed Willard’s Sooty Boubou, as opposed to the previously recognized high-elevation species, the Mountain Sooty Boubou. The Field Museum’s Fabio Berzaghi (now with the CEA Laboratory for Sciences of Climate and Environment in France) and his colleagues used museum records and bird survey records to analyze the ecological niche occupied by each species, and their results confirm that there is very little overlap between the ranges of the two species—Willard’s Sooty Boubou is found at approximately 1200–1900 meters and the Mountain Sooty Boubou at 1800–3800 meters. In Burundi, Rwanda, and Uganda, 70% of the potential for Willard’s Sooty Boubou lies outside of protected areas and has been converted to agriculture, and the numbers for the Democratic Republic of Congo are only slightly better.

Willard’s Sooty Boubou joins several other imperiled bird species that depend on the region’s mid-elevation forests, which have been largely overlooked by conservation efforts. “The Albertine Rift is a crossroads of amazing biodiversity, dramatic and diverse landscapes, and heartbreaking social and political unrest. It goes from glaciers to volcanoes to plateaus to lakes, with a succession of vegetation types from high-elevation cloud forests to lowland tropical forests,” says Berzaghi. “It is home to gorillas and forest elephants as well as a high number of endemic animal and plant species. Unfortunately, much of the region has gone through never-ending conflicts, with very negative consequences for both humans and biodiversity, and conservation involving local populations is paramount.”

“This paper provides additional data in support of the recognition of Willard’s Sooty Boubou as a species distinct from Mountain Sooty Boubou. Clarification of the niche that Willard’s Sooty Boubou occupies, that of mid-elevation forests, distinct from the higher-elevation Mountain Sooty Boubou, is important, because these habitats are among the most heavily impacted in Africa from agriculture,” according to UC Berkeley’s Rauri Bowie, an expert on African birds who was not involved in the study. “Conservation agencies have an opportunity to move beyond taxonomic debate and use the models derived from this species to improve conservation outcomes for not only this species, but also a broad set of mid-elevation Albertine Rift endemic vertebrates through protection of mid-elevation forests that have received relatively little protection in comparison to high-elevation montane habitats.”

Comparative niche modeling of two bush-shrikes (Laniarius) and the conservation of mid-elevation Afromontane forests of the Albertine Rift is available at http://americanornithologypubs.org/doi/full/10.1650/CONDOR-18-28.1.

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.