For Disappearing Bicknell’s Thrushes, Statistical Models are Lifesavers

Bicknell's Thrush, East Mt, Vermont
Bicknell’s Thrush (Photo Credit: Steve Faccio)

Bicknell’s Thrush has been identified as a globally vulnerable Nearctic-Neotropical migratory bird in need of serious conservation efforts. This species travels each year between its breeding grounds in the Canadian maritime provinces and upper northeastern United States and its winter home in the Greater Antilles. Males and females use different habitats in winter, with females preferring middle elevation forests that are more vulnerable to human disturbance than the higher, more remote forests used by males.   A new study from The Condor: Ornithological Applications identifies key habitat for females in the remaining fragmented montane wet forests of the Dominican Republic.

“Today’s multiple environmental threats and stressors (e.g., deforestation, predation by invasive species, climate change, bioaccumulation of heavy metal pollutants, etc.) are crafting an uncertain future for species with complex life cycles in their breeding grounds, stopover sites, and wintering grounds,” adds Eduardo E. Ingio Elias, a senior research associate of the Cornell Lab of Ornithology who was not involved with this research. “However, to conserve key suitable habitat for any species, ornithologists and land managers need to identify where that habitat is, what the population survival is within that habitat, and what threats birds face there.”

Vermont Center for Ecostudies scientist Kent McFarland and colleagues used a combination of field and GIS methods to predict areas that would be the best to conserve for Bicknell’s Thrushes. A model to predict Bicknell’s Thrushes’ distribution and habitat use was created using occurrence data and environmental variables collected from field surveys, combined with land cover data from remote sensing. Thrush presence and abundance in an area was best predicted by the combination of elevation (densities peaked at ~600 m), aspect (northeastern slopes), the amount of forest cover within 1 km, and forest density.

Lead author Kent McFarland emphasizes the importance of this work, which has demonstrated putting research into conservation action, “We used our results to help identify, purchase, and create the Dominican Republic’s first-ever private reserve, the 400-ha Reserva Privada Zorzal, where 70% of the land is to be forest and ‘forever wild’ while the remainder is for compatible crops such as organic chocolate. We are hoping that our work will be used to identify and prioritize additional lands for conservation of the Bicknell’s Thrush in the region and elsewhere.”

 

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Modeling spatial variation in winter abundance to direct conservation actions for a vulnerable migratory songbird, the Bicknell’s Thrush (Catharus bicknelli) is available at http://www.bioone.org/doi/full/10.1650/CONDOR-17-234.1.
Research contact: Kent McFarland, kmcfarland@vtecostudies.org

About the journal: The Condor: Ornithological Applications is a peer-reviewed, international journal of ornithology published by the American Ornithological Society. The journal began in 1899 and in 2016 The Condor had the number one impact factor among 24 ornithology journals.

For flickers, looks can be deceiving

Northern Flicker (male)
Red-shafted Flicker (Photo Credit: Glenn Lahde)

The North American woodpeckers known as “flickers” stand out for their distinctive wing and tail feathers of bright reds or yellows, and for their rampant interbreeding where these birds of different colors meet in the Great Plains. Despite the obvious visual differences between the Red-shafted Flicker of the west and the Yellow-shafted Flicker of the east, scientists have never before found genetic differences between them. A new study from The Auk: Ornithological Advances uses data from thousands of regions across the genome to distinguish these birds molecularly for the first time.

Stepfanie Aguillon and her colleagues at the Cornell Lab of Ornithology explored patterns across the genomes of these birds and find them to be incredibly similar at the molecular level. In spite of the strong similarity, they still have the ability to distinguish the western Red-shafted Flickers from the eastern Yellow-shafted Flickers for the first time through the use of new genomic methods. Genomic technology is advancing at such a rapid rate that genetic sequence differences that were undetectable in the 1980s using (then) cutting-edge methods are now readily apparent using next-generation sequencing techniques.

“Flickers have intrigued ornithologists and naturalists at least as far back as Audubon, but only recently has it become possible to understand these birds genomically,” says lead author Stepfanie Aguillon. “I was unsure what we would find, given how much trouble previous researchers have had with these birds. I was surprised—and excited—by how similar we found them to be since we now had thousands of markers across the genome. I think this paper underlies a theme that has become more and more apparent over the last few years—even when two birds look very different, they may not be very different genetically.”

“The hybrid zone between the yellow- and red-shafted flickers is particularly striking, but despite very apparent morphological and ecological differences, genetic studies beginning in the late 1980s found few differences between these two ‘subspecies,’” adds flicker expert William S. Moore, a Wayne State University professor who was not involved with this research. “Hybrid zones are often described as “natural laboratories” for studies on speciation. Despite the low level of genetic divergence across the flicker hybrid zone, it is certain that selection is operating on genes involved in plumage divergence and ecological adaptation. Aguillon’s study will be a foundation stone for studies that identify the adapted genes and will bring us to a new understanding of the processes of speciation.”

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A flicker of hope: Genomic data distinguish Northern Flicker taxa despite low levels of divergence is available at http://www.bioone.org/doi/full/10.1642/AUK-18-7.1
Researcher contact: Stepfanie M. Aguillon, sma256@cornell.edu

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.

Whiskered Auklets Lack Wanderlust, Are Homebodies Instead

Auk-17-235_Whiskered Auklet_Ian Jones
Whiskered Auklet (Photo Credit: Ian Jones)

A new study from The Auk: Ornithological Advances presents some of the best evidence that Whiskered Auklets are an outlier in the auklet family by not migrating and instead staying close to “home” (their breeding colonies) year-round. Most migratory birds lead two opposite lifestyles in the same year. During the breeding season a bird’s location is constrained and their habits are repetitive given a nest full of chicks that require food, warmth, and protection. For some birds it is the only time they congregate or otherwise come together. Comparatively, during the non-breeding season their only true task is to survive. Whether migratory or residential, as long as the bird makes it back to the breeding grounds to reproduce, they can go almost wherever they want. Whiskered Auklets are consistent through the year though and don’t wander far at all.

Carley Schacter and Ian Jones of Memorial University of Newfoundland used light-based archival geolocation tags on Whiskered Auklets in Buldir Island, Aleutian Islands, Alaska, to determine the locations of their full annual life cycle. The data they collected corroborated what researchers have long suspected. This species is unique in the auklet family for not migrating at all. Most seabirds roost on the water at night, but Whiskered Auklets stay in the vicinity of the breeding colony year-round and consistently return to roost at night on land. Such behavior may not only be unique to auklets, but to the entire seabirds group. How could this unusual adaptation have come about? Whiskered Auklets capitalize on the foraging habitat close to their breeding colony which reduces metabolic costs. Given the influence of tradeoffs on animal behavior and life history strategies, this foraging area could be a large contributor to their residential behavior.

But there are risks to this strategy as well. Lead author Carley Schacter notes, “While this non-migratory behavior is very interesting to us on a theoretical level, there are also important implications for the conservation and management of this most vulnerable of auklet species. Year-round residence near the breeding site (an area of high fishing and shipping traffic) makes Aleutian-breeding Whiskered Auklets even more exposed than previously thought to human threats such as oil/fuel spills and light attraction leading to fatal collisions with vessels. Their nocturnal roosting behavior also makes them especially vulnerable to introduced mammalian predators such as rats and foxes.”

“The authors found evidence for an almost unique adaptation of a seabird in a remote, difficult-to-work-in, and isolated environment,” adds Jeff Williams, Assistant Refuge Manager at the Alaska Maritime National Wildlife Refuge, who was not involved with this research. “We now know that Whiskered Auklets are particularly sensitive to human-caused disturbances (oil spills, light attraction, invasive species introductions etc.) and can incorporate this information into management planning.”

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Confirmed year-round residence and land roosting of Whiskered Auklets (Aethia pygmaea) at Buldir Island, Alaska is available at http://www.bioone.org/doi/full/10.1642/AUK-17-235.1
Researcher contact: Carley R. Schacter, crs634@mun.ca

About the journal: The Auk: Ornithological Advances is a peer-reviewed, international journal of ornithology that began in 1884 as the official publication of the American Ornithologists’ Union, which merged with the Cooper Ornithological Society in 2016 to become the American Ornithological Society. In 2009, The Auk was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.

Long-Term Study Reveals One Invasive Insect Can Change a Forest Bird Community

Condor-17-204_Acadian Flycatcher_D Williams
Acadian Flycatcher in Hemlock forest (Photo Credit: D Williams)

Eastern hemlock forests have been declining due to a non-native insect pest, the hemlock woolly adelgid. A new study from The Condor: Ornithological Applications presents some of the best long-term data showing how the decline of a single tree species (eastern hemlock) leads to the disappearance of birds specialized to those trees. The data also indicate birds associated with non-hemlock habitat features (deciduous forest, woodland edge, and shrubs) are spreading into former hemlock forests. A single insect species has led to a less diverse bird community across this landscape.

Pennsylvania State University’s Matthew Toenies and colleagues analyzed a long-term response to the decline of eastern hemlocks using vegetation and bird abundance surveys. The researchers took advantage of surveys they had conducted in 2000 before adelgids had caused hemlock decline and compared those data to new data from the same forests in 2015-16, after decline. They then analyzed how both individual bird species and groups of species responded to this habitat change.

The data showed that as hemlocks became less abundant in the forest, the bird species most associated with these trees also disappeared. As the hemlock-specific birds left, birds that are normally found in more general hardwood forests replaced them. Thus, biodiversity was reduced with the decline of hemlocks as well and the composition of the landscape became more similar over a larger area.

“Invasive species, climate change, and land-use change are all similar in that they make our world a less diverse place, and this study helps greatly in understanding how the loss of the eastern hemlock plays its own role in the degradation of biodiversity,” adds University of Connecticut Professor Morgan Tingley, a community ecologist who was not involved in this research.

Lead author Matthew Toenies says, “To sum up, to people who are saddened by the loss of hemlocks and the birds that rely on them, I would say one thing: We cannot turn back the clock–we cannot un-introduce the hemlock woolly adelgid; but we absolutely possess the power to prevent this story from repeating itself.”

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Shifts in vegetation and avian community structure following the decline of a foundational forest species, the eastern hemlock, is available at http://www.bioone.org/doi/full/10.1650/CONDOR-17-204.1.
Research contact: Matthew Toenies, mkt5213@psu.edu

 

About the journal: The Condor: Ornithological Applications is a peer-reviewed, international journal of ornithology. It began in 1899 as the journal of the Cooper Ornithological Club, a group of ornithologists in California that became the Cooper Ornithological Society, which merged with the American Ornithologists’ Union in 2016 to become the American Ornithological Society. In 2016, The Condor had the number one impact factor among 24 ornithology journals.

 

Birds play the waiting game in tough environmental conditions

Auk-17-206_wifl in hand_Tad Theimer
Banded Willow Flycatcher in the hand (Photo Credit: Tad Theimer)

Every animal’s ultimate goal in life is to generate offspring to pass on its genetic material to the next generation. But sometimes, resources are scarce and the task of reproduction is too difficult or risky. If resources are limited and tough to find, reproductive efforts may fail anyway. In these situations, it may be in an animal’s best interests to not defend a territory or to breed at all, but rather to focus its efforts on surviving to the next breeding season. Biologists refer to individuals without a territory during the breeding season as ‘floaters’. A new study from The Auk: Ornithological Advances presents some of the best evidence on how changes in environmental conditions, specifically droughts, impact the social and reproductive behavior of birds.

Tad Theimer of Northern Arizona University and colleagues monitored a population of Willow Flycatchers over a five-year period. Each individual in this population was marked with uniquely colored leg bands and its behavior recorded throughout the breeding season. Some of these birds defended territories that contained their nests, while other birds – the floaters – moved around the population declining territory and nest. A severe drought that occurred during the study allowed the researchers to examine how these birds respond to changes in the environment. They found there were one and a half times more floaters during the drought than during years with average rainfall, and that these floaters were more likely to survive than individuals that tried to nest. When the researchers compared how many chicks a bird had with their floater status the previous year, they found that territorial birds had more chicks than floaters – with one exception. In the year immediately after the drought, former floaters produced more chicks.

There is a potential twist in the story though because the researchers did not check the DNA of the chicks throughout the study. Birds are notorious for extra-pair copulations (or breeding with another individual that is not your mate), and it’s probable floaters engage in this behavior regularly. Through this behavior, they get the benefit of passing on their genes without the cost of raising the chick.

As lead author Theimer puts it, “In normal years all birds try to breed, and those that don’t breed lose out in long-term reproductive success, but in extreme drought years, not breeding is actually the better strategy”. But this strategy of patience assumes that next year will be better than this year. As climate change increases the frequency of these extreme environmental conditions, this assumption becomes less certain.

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Extreme drought alters frequency and reproductive success of floaters in Willow Flycatchers is available May 23, 2018, at http://www.bioone.org/doi/full/10.1642/AUK-17-206.1
Researcher contact: Tad Theimer, Tad.Theimer@nau.edu

 

About the journal: The Auk: Ornithological Advances is a peer-reviewed, international journal of ornithology that began in 1884 as the official publication of the American Ornithologists’ Union, which merged with the Cooper Ornithological Society in 2016 to become the American Ornithological Society. In 2009, The Auk was honored as one of the 100 most influential journals of biology and medicine over the past 100 years.