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.

Possible Oahu Populations Offer New Hope for Hawaiian Seabirds

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A juvenile Newell’s Shearwater. Photo credit: Lindsay Young.

The two seabird species unique to Hawaii, Newell’s Shearwaters and Hawaiian Petrels, are the focus of major conservation efforts—at risk from habitat degradation, invasive predators, and other threats, their populations plummeted 94% and 78% respectively between 1993 and 2013. However, a new study in The Condor: Ornithological Applications offers hope of previously undetected colonies of these birds on the island of Oahu, from which they were believed to have vanished by the late 1700s.

Shearwaters and petrels nest colonially in crevices, burrows, and under vegetation at mid to high elevations. They currently breed on other Hawaiian islands including Kauai and Maui, but were both believed to have extirpated from Oahu prior to European contact in 1778; biologists believed that occasional records from the island were birds thrown off-course at night by city lights.

Pacific Rim Conservation’s Lindsay Young and her colleagues used a spatial model based on elevation, forest cover, and illumination to identify potential suitable breeding habitat for both species on Oahu, then deployed automated acoustic recording units at 16 sites on the island to listen for the birds’ calls in 2016 and 2017, accessing remote mountain locations via helicopter. To their surprise, they detected petrels at one site and shearwaters at two sites.

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Automated acoustic recording units picked up the calls of endangered seabirds at remote locations on Oahu. Photo credit: Lindsay Young

“We were doing a statewide survey for these species for the U.S. Fish and Wildlife Service as part of recovery action planning, but Oahu was not initially included as one of the sites to survey, since evidence suggested they weren’t there,” says Young. “Since we’re Oahu-based, we thought we would at least put a few recording units out to see if there was anything. And we were surprised, to say the least, that we not only had calls detected, but detected both species across two years.”

These could be the last survivors of remnant breeding populations on Oahu, or they could be young birds from other islands that are searching for mates and breeding sites. “Either way, it gives us hope that we will be able to use social attraction—that is, using calls and decoys—to attract them nest on an island where they were once abundant,” says Young. Oahu birds could help boost connectivity between individual island populations and provide extra insurance in case any one island’s seabird population is decimated by an event such as a hurricane. As petrel and shearwater numbers continue to decline, protecting Hawaii’s remaining seabirds remains a major conservation priority in the region, and the possibility that they’re continuing to breed on Oahu provides new reason for optimism.

Evidence of Newell’s Shearwaters and Hawaiian Petrels on Oahu, Hawaii is available at https://academic.oup.com/condor/article/121/1/duy004/5298327.

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.

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.