Engineered Sandbars Don’t Measure Up for Nesting Plovers

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Piping Plovers were more successful nesting on natural sandbars than engineered ones. Photo credit: D. Borden

Dams alter rivers in ways that reduce the creation of natural sandbars, which is bad news for threatened Piping Plovers that depend on them for nesting habitat. Between 2004 and 2009, more than 200 hectares of engineered sandbars were built along the Missouri River to address the problem—but how does this engineered habitat compare to the real thing? A new study from The Condor: Ornithological Applications takes advantage of a natural experiment created by the region’s 2011 floods, demonstrating that the engineered habitat doesn’t provide the benefits of sandbars created by nature.

Kelsi Hunt of the Virginia Polytechnic Institute and State University and her colleagues collected data downstream of Gavins Point Dam from 2005 to 2014, monitoring more than 1,000 nests and banding almost 3,000 individual birds both before and after massive floods in 2011 created vast new areas of natural sandbar habitat. Nest success, chick survival, and total reproductive output all increased after the flood and remained high as flood-created sandbars began to age, even without the intensive predator management that had been done on the engineered sandbars. In contrast, Piping Plover populations nesting on engineered sandbars grew in the first year after the habitat’s construction, but there wasn’t enough space to go around—high population densities quickly led to high risk from predators and decreased reproductive rates.

“I realized just how interesting of a natural experiment the flood provided us with when my advisor and I boated the entirety of the Gavins Point Reach prior to the 2012 field season,” says Hunt. “The amount of sandbar habitat that the 2011 flood created was incredible to see. Where before there was just river, huge sandbars replaced it. Some of the sandbars it created were larger than city blocks and took hours to survey.” She hopes that managers can learn from this study to create better engineered habitat for sandbar-nesting birds, building more nesting space at one time and constructing new habitat close to existing sandbars so that young birds will have an easy time finding and colonizing it.

“This paper presents a clear contrast in demographic rates of Piping Plovers in naturally created and human-restored habitats that can be used to compare and refine conservation strategies,” adds Anne Hecht, Piping Plover recovery coordinator for the U.S. Fish and Wildlife Service. “Although it focuses on Missouri River sandbars, it has important implications for conservation of Piping Plover habitat rangewide, as well as for other species experiencing disruption of habitat formation processes.”

Demographic response of Piping Plovers suggests that engineered habitat restoration is no match for natural riverine processes is available at http://www.bioone.org/doi/full/10.1650/CONDOR-17-93.1.

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.

AUTHOR BLOG: Call Variation Suggests Roles for Natural History & Ecology in Marsh Bird Vocal Evolution

Sarah Luttrell

Linked paper: Geographic variation in call structure, likelihood, and call-song associations across subspecies boundaries, migratory patterns, and habitat types in the Marsh Wren (Cistothorus palustris) by S.A.M. Luttrell and B. Lohr, The Auk: Ornithological Advances 135:1, January 2018.

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Marsh Wrens’ calls vary across their geographic range. Photo credit: S. Luttrell

Many bird species have unique geographic signatures in their vocalizations similar to human “accents.” Most of what we know about geographic variation in bird sounds comes from studies of bird song. Song has been a rich subject for studying geographic variation because it is typically learned, allowing song to change more quickly across space and time than a purely genetic trait. Song, however, is only one type of signal in a bird’s vocal repertoire. We wanted to build a broader picture of how vocal behavior evolves and changes among populations by looking at a large repertoire of sounds at once. Most birds have multiple call types in addition to their songs. Each call or song type is an individual trait used under unique circumstances, and that means that each one may be under different selective pressures. As a result, looking at multiple vocalizations may reveal multiple patterns of geographic variation, or, if their geographic patterns are similar, it may suggest a general process of vocal evolution. There are many ways in which vocalizations might change over time or distance. For example, changes could be random—as long as the signal still sends the correct message, some aspects of its acoustic structure could drift among populations. Additionally, vocal signals may be under selection to reduce distortion caused by the habitat in which they are produced and heard. Think about how sounds are distorted differently in an open, bare hallway versus a musician’s sound booth and how the local acoustics might alter a listener’s ability to understand you. Furthermore, if some aspect of the sound is learned, then copy errors or innovations during learning can result in passing down cultural changes over time. These are just a few ways in which sounds might be altered, and no two vocalizations are necessarily influenced in the same way by the same set of selective pressures.

In order to compare vocal repertoires among populations, we looked at several subspecies of the Marsh Wren. Marsh Wrens provide a natural experiment in vocal variation due to ecological and natural history differences among the subspecies. The five eastern North America subspecies we focused on are found in two distinct habitats (freshwater marshes and saltmarshes), and they exhibit three migratory patterns (resident, partially migratory, and fully migratory). Our first challenge was to describe and classify the call repertoire for Marsh Wrens. We identified seven discrete call types. Three of the seven calls varied in acoustic properties that were consistent with differences in either migratory pattern or habitat type. Surprisingly, we also found that four calls were more common in some subspecies than others and that the differences were greatest between habitat types. This variation in call production may indicate differences in behavior or timing of breeding among the subspecies with different ecologies. Our results suggest that while not all vocal signals are changing at the same rate or in the same way, differences in habitat type and migratory behavior may be related to the biggest differences in vocal behavior. Interestingly, the calls that showed the greatest differences were calls used in mate attraction and territory defense, while calls related to alarm or distress were similar across subspecies, natural history, and habitat type. This result suggests that sexual selection could be driving or reinforcing changes between populations with different ecologies.

In the future, we are excited to explore another unusual phenomenon that we report in this paper: the use of calls as embedded elements in song. Like most songbirds, Marsh Wren males sing during the breeding season to attract mates and defend territories. Unlike those of most songbirds, we found that, depending on the subspecies, 73-93% of male Marsh Wren songs contained embedded calls. Do embedded calls confer some additional message to the song? Does this behavior vary across the breeding season? Are there specific structural rules regarding the embedded call pattern within song? Stay tuned as we untangle the structural complexity and geographic variation in songs with embedded call elements in Marsh Wrens across the rest of their range. Does your study species use calls in a song-related context? If so, contact us at luttrell.sa@gmail.com—we would be excited hear about it!

Wrens’ Calls Reveal Subtle Differences Between Subspecies

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Biologist Sarah Luttrell records the calls of a Marsh Wren. Photo credit: S. Luttrell

Birds’ songs and the ways they vary between places have been well studied–but what can the simpler vocalizations known as calls tell us about bird biology? A new study from The Auk: Ornithological Advances provides the first detailed description of how Marsh Wren calls vary across eastern North America and hints at the evolutionary processes playing out between wren subspecies.

The University of Maryland Baltimore County’s Sarah Luttrell and Bernard Lohr recorded the calls of five Marsh Wren subspecies at nineteen different sites, encompassing the Gulf Coast, Atlantic Coast, and Great Lakes regions and including migratory, nonmigratory, freshwater marsh, and saltwater marsh populations. Categorizing the recordings into seven different call types, they analyzed how calls differed between subspecies. While some calls were associated with territory patrol, nest building, and courtship, others were used mainly during aggressive encounters with predators or other wrens. Both the acoustic characteristics of some calls and how frequently they were used differed from place to place.

“It was certainly a lot of work to compile data on multiple vocalizations and compare the results, but in the end, it makes for a more nuanced understanding of how various evolutionary processes shape animal behavior as a whole,” says Luttrell. “Twitter” calls differed between migratory and nonmigratory subspecies, for example, while “buzz” and “trill” calls differed between birds that lived in freshwater and saltwater marshes; while differences in habitat can’t directly explain this, all of these call types could be shaped by sexual selection that reinforces the boundaries between subspecies. Atlantic Coast populations produced the “chuck” alarm call more often than others, which suggests they may experience more threats from predators or nest at higher densities that lead to more antagonistic encounters between birds.

Could these differences eventually prompt Marsh Wren populations to diverge into fully separate species? “That’s impossible to say for sure—it all depends on the course that evolution takes!” says Luttrell. “We were excited that the patterns of call variation we observed seemed to coincide with differences ecology and life history, which suggests the possibility that these subspecies are evolving in different directions. In the future, we’re hoping to do some behavioral tests that might help us understand how much the acoustic differences matter to the birds’ behavior in the wild. If we do find that individuals respond less strongly to the vocalizations of another subspecies than to their own, then that would be additional evidence that at least some subspecies are on a trajectory of divergence.”

“This study highlights the diversity of calls that can be found in a single avian repertoire, and nicely illustrates how different elements of those repertoires can evolve independently,” according to the University of Northern Colorado’s Lauryn Benedict, an expert on communication in wrens and other songbirds. “The demonstrated patterns of call use in relation to behavioral context, caller sex, habitat, and migratory behavior raise many future avenues of inquiry. Avian calls are a generally understudied vocalization, and this paper demonstrates how and why we all should pay them more attention.”

Geographic variation in call structure, likelihood, and call-song associations across subspecies boundaries, migratory patterns, and habitat types in the Marsh Wren (Cistothorus palustris) is available at http://americanornithologypubs.org/doi/full/10.1642/AUK-17-110.1.

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.

AUTHOR BLOG: Understanding How Management Affects a Flagship Reed Bed Bird Species

Thomas Oliver Mérő

Linked paper: Reed management influences philopatry to reed habitats in the Great Reed-Warbler (Acrocephalus arundinaceus) by T.O. Mérő, A. Žuljević, K. Varga, and S. Lengyel, The Condor: Ornithological Applications 120:1, February 2018.

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A color-banded singing Great Reed Warbler male, April 2015.

Wetlands are inhabited by disproportionately large number of plants and animals and yet are among the most endangered habitats worldwide due to human-caused habitat loss and fragmentation. Ecologists and conservation biologists work hard on saving wetlands by using various techniques such as vegetation management (e.g. breaking up homogeneous reed beds), water regulation (e.g. maintaining a flood/drought cycle), or reintroduction of extinct species (e.g. cranes in the U.K.). Several recent studies have shown that the management of wetlands such as reed beds by controlling the water level and removing the vegetation by mowing, burning, or grazing can increase species richness and diversity; however, we know less about whether such management provides better conditions for survival and reproduction of single species whose presence is important to other species.

The Great Reed Warbler (Acrocephalus arundinaceus) is an Old World, long-distance migrant bird that breeds in reed habitats of the Western Palearctic and winters in sub-Saharan Africa. In central Europe, the Great Reed Warbler is a widespread breeder inhabiting almost all types of reed habitats (ponds, marshes, canals etc.). Great Reed Warblers arrive in mid-April from their wintering grounds and stay until the end of breeding season in late July.

We have studied the breeding ecology of Great Reed Warblers in northern Serbia for eight years. The region hosts a nice array of wetland habitat types, ranging from oxbows of the Danube to small and large canals, and from sand and clay mining ponds to marshes in natural depressions. For our work, we distinguished six types of reed habitats based on our own observations and information from local water management companies. The six types, which differ in their shape, size, vegetation cover, and water regime, are mining ponds, marshes, large canals, and three classes of small canals.

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Although large canals are preferred by large-winged, probably high-quality, males for nesting, this habitat type provides suboptimal conditions for breeding due to high brood parasitism by Cuckoos; therefore, this habitat type likely functions as an ecological trap.

These wetlands are managed by reed mowing and burning, which led us to wonder how reed management influences the birds and other wetland animals. Specifically, we were interested in whether and how management influences the survival and reproduction of Great Reed Warblers, a flagship species of lowland wetlands in central Europe. Reed management by burning and mowing offered a good opportunity to study the responses of Great Reed Warblers in each of the reed habitat types. For example, we recognized early on that larger-winged, presumably higher-quality, males tend to occupy reed habitats with little management and deep, stable water, which are typically found along large canals.

We color-banded all individuals (both adults and hatch-year birds) from the beginning of our study and regularly checked all reed beds every year during the nesting season to explore potential differences in survival and reproduction of birds in the six reed habitats. We were also curious to find out how reed management and water availability influence survival and reproduction. We first analyzed data on survival and encounter probability that were collected over seven breeding seasons (2009-2015).

We found that the encounter probability of birds banded as hatch-year birds was higher in reed habitats with shallower water, while that of those banded as adults was higher in reed habitats with deeper water. These opposite relationships between hatch-year birds and adults may indicate that experienced adults occupy qualitatively better habitats, similarly to large-winged males (mentioned above). When data were analyzed separately for the sexes, we found that the encounter probability of males depended on variation in reed management and in water depth. In contrast, for females, encounter probability depended only on water depth, i.e. encounter probability increased with water depth. Furthermore, most of the adults and hatch-year birds returned to the reed habitat that they had been occupying initially, indicating that Great Reed Warblers display unexpectedly high fidelity to the reed habitat type they hatched in or bred in before.

How do these results translate to management recommendations? We all want the best possible management for the birds we admire and study. Evidence found in our study showed that reed management by mowing and/or burning influences return rates of juveniles and adult males and females in different ways. These results suggest that in practice, spatially variable reed management should be applied and water with varying depths should be maintained to maximize the return rates of Great Reed Warblers. This is often easier said than done. However, the multitude of reed habitats in our study and the good working relationships we developed with water management authorities and other stakeholders will allow more detailed, experimental studies of the influence of management and the allocation of optimal combinations of management for the benefit of wetland birds.

AUTHOR BLOG: A New Species of Antbird

Andre Moncrieff

Linked paper: A new species of antbird (Passeriformes: Thamnophilidae) from the Cordillera Azul, San Martín, Peru by A.E. Moncrieff, O. Johnson, D.F. Lane, J.R. Beck, F. Angulo, and J. Fagan, The Auk: Ornithological Advances 135:1, January 2018.

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A male Cordillera Azul Antbird. Photo credit: A. Spencer

It was July 10, 2016, when Dan Lane, Fernando Angulo, Jesse Fagan, and I rolled into the coffee-growing town of Flor de Café in north-central Peru. This town lies in the Cordillera Azul—a picturesque series of outlying Andean ridges hardly explored by ornithologists. In fact, the first ornithological inventory in the region was only in 1996, when a team of researchers from the Louisiana State University Museum of Natural Science (LSUMNS) bushwhacked into the extremely remote eastern Cordillera Azul. It was on this expedition that Dan, then a beginning graduate student at LSU, discovered the distinctive Scarlet-banded Barbet (Capito wallacei) on “Peak 1538.” Now, twenty years later, we were back to see this iconic species, which graces the cover of the Birds of Peru field guide.

Flor de Café, in the somewhat more accessible western Cordillera Azul, has become the hub for barbet-chasers since LSUMNS associates Todd Mark and Walter Vargas confirmed its presence here in 2011. Thus, we were not surprised to run into another birdwatcher, Josh Beck, as we moved our gear into the single guest house in town. Within moments of meeting, Josh began telling us of a strange, ground-walking antbird he had encountered the previous day and documented with a sound recording. We quickly realized that his bird was a species new to science.

Fast forward a year and a half. This month, December 2017, The Auk is publishing the formal description of the Cordillera Azul Antbird (Myrmoderus eowilsoni). Based on our initial visit and a follow-up expedition led by LSU graduate student Oscar Johnson, we’ve learned a few things about this new species: its closest relative is the Ferruginous-backed Antbird (of which the nearest populations are about 1,500 km to the east in lowland forests of Brazil), it eats insects, the males and females sing different songs, it lives in pristine understory of humid forest, and its future near Flor de Café is very grim.

Chainsaws were an overwhelming component of the soundscape around town. We even asked some locals to delay cutting activities so that we could get better voice recordings of the antbird. Sun-coffee farming, which necessitates clear-cutting, is the main source of income for the residents of Flor de Café. By contrast, birding ecotourism benefits only a few residents, leading to some unfortunate and ongoing tensions within the town. There is clearly a great need for environmental education and conservation work in the region.

What I haven’t yet mentioned is that Flor de Café is located very near the Cordillera Azul National Park, which was created in 2001 and contains over 13,500 km2 of pristine habitat. We are very optimistic that future exploration within the park will produce new localities for the antbird and barbet, both presently facing severe habitat loss around Flor de Café.

From an ornithological perspective, the Cordillera Azul remains mysterious and tantalizing. Perhaps it holds a new hummingbird or tody-tyrant? Regardless of any future discoveries to be made in the Cordillera Azul, I hope that the new antbird brings attention to the incredibly biodiverse and distinctive avifauna of the region. I also hope that this discovery serves as a potent reminder of how far we still have to go in cataloging the diversity of life on this planet!

Urban Cooper’s Hawks Outcompete Their Rural Neighbors

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An urban-dwelling Cooper’s Hawk. Photo credit: B. Millsap

Depending on whether a species flourishes in a city environment, urban wildlife populations can be “sources” or “sinks,” either reproducing so quickly that individuals leave to colonize the surrounding area or needing constant immigration from outside to stay viable. A new study from The Condor: Ornithological Applications examines the population dynamics of Cooper’s Hawks in urban Albuquerque, New Mexico, and finds that city-born birds aren’t just thriving—they’re actually forcing their rural neighbors out of their nest sites.

New Mexico State University’s Brian Millsap collected data on Cooper’s Hawks living in a 72 square kilometer area of northeast Albuquerque from 2011 to 2015, monitoring each year’s nests and tracking newly fledged females with radio transmitters. He found that 30 times more hawks emigrated out of the urban area than immigrated into it, suggesting it was a source population for the surrounding region. However, the details didn’t fit neatly with the traditional source–sink model. While the surrounding exurban hawk populations were breeding and surviving well enough to sustain themselves without immigration, females moving out of the urban area were able to beat them to their nesting sites—unlike their exurban neighbors, they didn’t migrate south for the winter.

White-winged Doves, which first became established in the area in the 1980s, provide an abundant food source for city-dwelling hawks. “Individuals living in urban Albuquerque actually have a fitness advantage over their neighbors living in natural habitats. This advantage comes from the higher prey populations in urban areas, which allow urban female Cooper’s Hawks to spend the winter near their eventual breeding sites, as opposed to rural females that migrate south in winter,” explains Millsap. “The urban female hawks begin searching out and claiming nesting territories before the rural hawks return in spring and thus obtain nesting sites without direct competition from migrants. Because of this advantage, the urban Albuquerque Cooper’s Hawk population not only supports itself but also serves as a substantial source of immigrant females for surrounding native habitats.”

Changes in migratory behavior that lead to segregation between different groups can have profound effects on populations, altering how they interact both with each other and with other species in a community. According to the Peregrine Fund’s Chris McClure, an expert on raptor ecology, “This study is a great example of how solid field work and sophisticated modeling can yield new insights in basic and applied ecology.”

Demography and metapopulation dynamics of an urban Cooper’s Hawk subpopulation is available at http://www.bioone.org/doi/full/10.1650/CONDOR-17-124.1.

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.

Timing of Migration Is Changing for Songbirds on the Pacific Coast

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Volunteers collect data on captured songbirds. Photo credit: San Francisco Bay Bird Observatory

Changes in the timing of birds’ migration can have serious negative effects if, for example, they throw the birds out of sync with the food resources they depend on. A new study from The Condor: Ornithological Applications uses a long-term dataset from the Pacific coast and shows that the timing of bird migration in the region has shifted by more than two days in both spring and fall over the past two decades.

Gina Barton and Brett Sandercock of Kansas State University used 22 years of data from the San Francisco Bay Bird Observatory in northern California, where researchers captured and marked migrants as they passed through each year. Examining how migration timing was related to three indices of climate variation, including El Niño, they focused on five species—the Pacific-slope Flycatcher, Orange-crowned Warbler, and Wilson’s Warbler, which are short-distance migrants, and the Swainson’s Thrush and Yellow Warbler, which are long-distance migrants. They found that, over time, birds had been migrating earlier in spring and later in fall. About one third of this change in timing was explained by variation in climate indices, suggesting that some western songbirds can respond flexibly to changing environmental conditions. However, the two long-distance migrants had smaller changes in timing that were not as closely linked to climate indices.

The study of the timing of cyclic natural phenomena such as migration is known as phenology. “Long-term studies are valuable for understanding changes in the seasonal phenology of migratory birds and other organisms,” says Sandercock. “Our results join growing evidence that long-distance migrants may be less able to cope with rapid environmental change. However, the potential impacts of changing phenology on songbird population dynamics are difficult to predict, in part because our understanding of the migratory behavior of western songbirds remains incomplete.”

Sandercock adds that long-term projects like this one wouldn’t be possible without the commitment of many funders, technicians, and volunteers. “Our project was made possible by the dedicated efforts of many volunteers who assisted the staff of the San Francisco Bay Bird Observatory with systematic mist netting at the Coyote Creek Riparian Station. The long-term continuity could not have been maintained without stable financial support from funding by the Santa Clara Valley Water District, and the Pacific Gas and Electric Company.”

Long-term changes in the seasonal timing of songbird migration on the Pacific Flyway is available at http://www.bioone.org/doi/full/10.1650/CONDOR-17-88.1.

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.

Gina is now a Director for Cheesemans’ Ecology Safaris, an ecotourism company in Los Gatos, California. Brett is now a Senior Research Scientist with the Norwegian Institute of Nature Research in Trondheim, Norway.