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.

AUTHOR BLOG: Manage hunting and the rare can once again become the common

Lucía Vargas and Andrew Whitworth

Linked paper: Secondary forest is utilized by Great Curassows (Crax rubra) and Great Tinamous (Tinamus major) in the absence of hunting by A. Whitworth, C. Beirne, E. Flatt, R.P. Huarcaya, J.C.C. Diaz, A. Forsyth, P.K. Molnár, and J.S.V. Soto, The Condor: Ornithological Applications 120:4, November 2018.

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Great Curassows and Great Tinamous are tropical gamebird species that are highly threatened by hunting and deforestation.

In one of the most biologically diverse rainforests of the world, the Osa Peninsula of Costa Rica, curassows and tinamous are thriving by hiding from hunters in protected, regenerating forests. These forests were once grasslands and disturbed forests that were hunted out. We have found that conservation efforts by the nonprofit group Osa Conservation (www.osaconservation.org) have been efficient for protecting these stunning gamebirds.

Game birds are important seed dispersers, control insect populations, and are food for many mid-level and apex predators. They provide social and economic services and are a source of protein, materials, and economic income from birding tourism. However, deforestation and hunting are leading causes of declines in populations of game birds such as the Great Curassow (Crax rubra) and the Great Tinamou (Tinamus major). The Great Curassow, for example, had lost 69% of its original habitat by 1977, and hunting was responsible for greatly reducing many populations, to the point of local extirpation in some regions. We wanted to know how valuable recovering habitats can be for such species, providing that hunted is controlled.

The field work to set up 60 camera traps during the very hot dry season was intense. It can be tricky to determine what factors play a role in habitat choice, but we had an ideal study site. Our grid covered a relatively small protected area (free from hunting) that comprises several different habitat types: old-growth primary forest, naturally regenerating secondary forest, recovering secondary plantation forests, and active agricultural land. Moreover, we analyzed the influence of roads, rivers, elevation, and whether cameras were located on or off trails, all of which are known to influence the distribution of rainforest wildlife.

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Camera traps minimize researcher–bird contact and provide an effective means to study elusive ground-dwelling bird species. Here, Eleanor Flatt from Osa Conservation’s team, a co-author of the article, sets up a camera.

Both bird species chose to use secondary growth forest frequently, despite being described in other studies as primary forest specialist species. This is likely due to the eradication of hunting since the establishment of Osa Conservation in 2002, the close proximity of remaining old-growth forest tracts, and the fact that the regenerating forests have had over 45 years to recover.

One surprising result from our data was that Great Curassows are more likely to be seen near roads. This makes sense when we consider that they are likely benefitting from a higher abundance of fruiting trees, but they must be careful, because this could also result in what is known as an ecological trap. If hunting were to return, roads would provide easy access for hunters. On the other hand, although the tinamous utilized all types of forest, they very clearly avoided agricultural land. Even the forest strips in farm areas are not sufficiently safe and cozy for the Great Tinamou—they like it cool, dark, and well-connected.

Our study demonstrates the significance of protecting wildlife from hunting through understanding spatial behavior. What would the results be like at another site? In a place with no source population nearby to allow for natural recolonization as the forests recover, could we reintroduce and reestablish these species once hunting has been controlled?

Their importance as rainforest seed dispersers will affect the pathway of regeneration and growth of secondary forests, and their presence will also provide food for predators like ocelots and margays, assisting their recovery as well. “Secondary” forests don’t mean second-rate habitat—instead, they mean that wildlife and people have a second chance.

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AUTHOR BLOG: A new hummingbird species in Ecuador

Juan Freile

Linked paper: A striking, critically endangered, new species of hillstar (Trochilidae: Oreotrochilus) from the southwestern Andes of Ecuador by F. Sornoza-Molina, J.F. Freile, J. Nilsson, N. Krabbe, and E. Bonaccorso, The Auk: Ornithological Advances 135:4, October 2018.

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Adult male (above left, center right), adult female (below), and immature male (above right) Oreotrochilus cyanolaemus. Image credit: P. Greenfield.

Last year a new hummingbird species was unexpectedly discovered on a seldom-visited mountain top in southern Ecuador. A brief visit to the rocky outcrops of Cerro de Arcos in the southern province of El Oro produced a photographic record that rang a bell: a mysterious immature male clearly assignable to the genus Oreotrochilus, the hillstars, which included six species at the time. A few days later, an adult male was captured in another photo, and a week after that, several males and females were observed and a handful collected for scientific purposes.

Such an outstanding discovery needed a thorough assessment to understand the taxonomic status and phylogenetic relationships of the putative new species and their evolutionary implications for the genus Oreotrochilus. This genus is remarkable in being the one that reaches the highest elevations: records above 4,500 meters, with a mean of 3,600 meters above sea level. As such, these hummingbirds need a very special set of physiological and behavioral adaptations to feed on the scarce nectar resources available. One plant in particular is extremely important for the hillstars—the spiny-leaved Chuquiragua, with its fire-orange flowers.

The newly discovered hillstar of southern Ecuador is not an exception in its feeding associations. In fact, its geographic range seems to be shaped by the availability of Chuquiragua in a very restricted region between the geographic ranges of the Ecuadorian Hillstar, Oreotrochilus chimborazo, found in Ecuador and extreme southern Colombia, and the Green-headed Hillstar, Oreotrochilus stolzmanni, found in Peru and extreme southern Ecuador.

The latter species is likely the closest relative to the new species, sharing an overall plumage pattern and being very similar genetically. But a single striking characteristic sets them apart: the Green-headed Hillstar has a glittering lime-green throat patch, or gorget, whereas the gorget in the new species is a glittering deep blue. Given that gorgets are likely used in courtship displays by males, the strikingly different color suggests that reproductive isolation is effectively segregating these taxa.

Being extremely restricted in distribution, confined to a few mountain tops where habitat degradation is dramatic, the conservation status of this new hillstar seems critical. No conservation projects exist across its tiny range; on the contrary, the agricultural boundary is progressing, cattle graze free in the few natural grasslands that remain, burns are frequent every windy summer, and not a few mining concession cover the area. Urgent research and conservation actions are on the way, but there is little time left.

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.

AUTHOR BLOG: “Bird-in-the-middle”—a mid-elevation tropical species stuck in limbo

Fabio Berzaghi & John Bates

Linked paper: Comparative niche modeling of two bush-shrikes (Laniarius) and the conservation of mid-elevation Afromontane forests of the Albertine Rift by F. Berzaghi, J.E. Engel, A.J. Plumptre, H. Mugabe, D. Kujirakwinja, S. Ayebare, and J.M. Bates, The Condor: Ornithological Applications 120:4, October 2018.

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A search through the tropical forest literature for “mid-elevation forests” reveals relatively few results compared to a search for high-elevation or lowland forests, and looking at a map of protected areas and land cover in mountainous tropical regions makes it clear why. For example, in the African Albertine Rift, most national parks tend to be in high elevation areas where slopes are steep and land conversion for human use is more difficult. As we move down the slopes, the habitat starts degrading until we arrive in the lowlands, where almost no intact habitat remains, particularly on the eastern side of the Rift.

In 2010, Voelker et al. described a new species of bush-strike, the Willard’s Sooty Boubou (Laniarius willardi), and noticed that this species occurs at lower elevations than its sister species, the Mountain Sooty Boubou (Lanarius poensis). We were thus wondering how much habitat was left for this mid-elevation species, knowing that in this region lower-elevation forests are degraded or have been converted to agriculture. Using niche modeling and land cover data, we discovered that these two species of birds reside at different elevations across a small portion of montane Africa, overlapping only in part. Unfortunately, the habitat for L. willardi has been greatly reduced, because mid-elevation forests are outside protected areas and national parks. L. willardi may not be able to move to higher elevations, as its preferred environmental conditions are between 1200 and 1900 meters; a large portion of its suitable habitat is found in the Democratic Republic of the Congo’s Itombwe Plateau, technically a protected area but problematic to protect.

The plight of L. willardi is probably similar to that of many other mid- and low-elevation species in the area. Even though our results are not such good news for birds and other mid-elevation species in the region, we also want to highlight the importance of scientific collaborations with local researchers and conservation units. These collaborations help us define habitats and species in need of attention. Importantly, the authors of our study are a combination of Africans and non-Africans, with a range of research foci including ornithology and conservation but also niche modeling and bioinformatics. The data used in our study are based on both museum specimens (historical and modern) and modern field observations, which were carried out by teams that always included African students and scientists from the countries where the data were collected. Conservation can only be successful in the long run if in-country capacity for conservation science is developed around the world.

The discovery of L. willardi and its description were made possible through modern scientific collection during collaborations between local Albertine Rift ornithologists and the Field Museum. Data from such modern collections will help clarify lingering concerns in the taxonomic community (particularly Birdlife International and the IUCN) in regards to the status of these two species relative to other black boubous occurring far to the west in the Cameroonian Highlands. Work like this has great value, because it allows highlighting issues of conservation concern at both regional and local scales. Each region of the Albertine Rift has its own history and ongoing issues with deforestation, instability and protection. There is no “one size fits all” solution to conservation in the Albertine Rift, but this paper helps emphasize that there is regional expertise in the form of researchers and conservation professionals who will make a difference. Opportunities to work with international colleagues to combine conservation and science, as in this paper, will be instrumental in building efforts to protect the incredible biota of this wonderful region.