AUTHOR BLOG: Flooding, Predators, and an Imperiled Sparrow

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A banded adult Saltmarsh Sparrow female foraging in Scarborough, ME. Photo credit: D. Hitchcox

Kate Ruskin

Linked paper: Demographic analysis demonstrates systematic but independent spatial variation in abiotic and biotic stressors across 59 percent of a global species range by K.J. Ruskin, M.A. Etterson, T.P. Hodgman, A.C. Borowske, J.B. Cohen, C.S. Elphick, C.R. Field, R.A. Longenecker, E. King, A.R. Kocek, A.I. Kovach, K.M. O’Brien, N. Pau, W.G. Shriver, J. Walsh, and B.J. Olsen, The Auk: Ornithological Advances 134:4, October 2017.

Ecologists have long hypothesized that the factors that affect a species vary over its geographical range. For example, cold climates may limit survival at higher latitudes, while competition with other species may be more important at lower latitudes. Scientists have proposed that this sets up a tradeoff for each species, favoring individuals that are physiologically hearty to harsh abiotic conditions at higher latitudes and individuals that are good competitors at lower latitudes.

With the help of 14 coauthors scattered across the northeastern U.S., I collected demographic data on Saltmarsh Sparrows to test whether this pattern was supported. Our team, known as the Saltmarsh Habitat and Avian Research Program (SHARP), conducted coordinated demographic research on Saltmarsh Sparrows at 23 sites in 7 states from Maine to New Jersey. We searched for nests, revisited them every few days throughout the breeding season, and classified each as successful or failed due to various causes.

Saltmarsh Sparrows breed exclusively in high marsh habitat, which is the zone of tidal marshes that typically floods monthly during the astronomical high tides. Saltmarsh Sparrows build their nests in the short grasses of the tidal marsh, just a few inches above the ground. As a result, nests often fail due to flooding during the high monthly tides. Most nest failure in Saltmarsh Sparrows is caused either by this nest flooding, or by depredation.

Footage captured by University of Connecticut graduate student Samantha Apgar.

Using monitoring records from 837 nests collected across our study sites, we observed patterns in the factors that limit nest survival that varied predictably across hundreds of kilometers. We found that the biotic stressor, nest depredation, increased toward lower latitudes, which is consistent with the Asymmetric Abiotic Stress Limitation (AASL) hypothesis. AASL proposes that populations are limited by biotic stressors like nest depredation at the lower latitudes of their range, while abiotic stressors such as climate limit populations at higher latitudes. Conversely, we observed that the abiotic stressor, nest flooding, did not vary with latitude. Instead, nest flooding was best predicted by indicators for regular monthly flooding as well as irregular flooding events, which varied independent of latitude. Our results suggest that stressors to Saltmarsh Sparrow reproductive success vary systematically across its range, but independently from each other. Therefore, we did not observe the tradeoff between physiological heartiness at higher latitudes and competitiveness at lower latitudes that is predicted by the AASL hypothesis.

In addition to the insight this example provides into how different stressors limit species across their ranges, the patterns of biotic and abiotic stress that we observed provide information relevant to conservation of the Saltmarsh Sparrow. The Saltmarsh Sparrow is considered threatened by the International Union for the Conservation of Nature, and SHARP researchers have found that the Saltmarsh Sparrow population is small, declining, and expected to go extinct this century. For example, our results suggest that predator control may be an effective method for improving Saltmarsh Sparrow fecundity toward the low latitudes of its range, but not farther north.

This new article in Auk: Ornithological Advances is the latest in a series we have written about the Saltmarsh Sparrow and other tidal marsh birds found in northeastern North America, many of which are facing population declines and habitat change. Learn more about tidal marsh birds and SHARP’s research at our website (www.tidalmarshbirds.org) and Facebook page (www.facebook.com/tidalmarshbirds).

Songbird Populations May Indicate Trouble in Northwestern Forests

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Purple Finches, an indicator of healthy coniferous habitat, are declining in the Northwest. Photo credit: J. Livaudais

Populations of many North American songbirds are declining, and in many cases we don’t understand why—for example, whether the problem lies with reproductive success or in the survival rates of adults. Conservation efforts need this information to be effective, and bird banding stations can help fill in the gaps, providing insights into how demographics vary across space and time. A new study from The Condor: Ornithological Applications presents ten years of data from banding stations across northern California and southern Oregon and offers new hints on what’s driving changes in the region’s songbird populations.

The Klamath Bird Observatory’s Sarah Rockwell and her colleagues used data collected at ten of the observatory’s bird banding sites between 2002 and 2013 to estimate the abundance and reproductive productivity of twelve songbird species, all either of regional conservation concern or indicators of coniferous or riparian habitat quality. They found that three species (the Purple Finch, Yellow-rumped Warbler, and Dark-eyed Junco), all indicators of coniferous habitat, were declining across the region, while two (the Yellow-breasted Chat and Black-headed Grosbeak) were increasing, though the trends varied from site to site. While breeding productivity declined in three species, adult abundance was correlated with the previous year’s productivity for only one species, the Yellow Warbler, suggesting that local productivity is not the primary culprit behind population declines.

“Before we can understand the impact of threats to bird populations, we first need to understand what’s happening where,” says John Alexander, the Executive Director of the Klamath Bird Observatory and a coauthor on the work. “This study presents trends from regional-scale monitoring and just begins to scratch the surface of understanding population dynamics, variation in demographic rates, and drivers of population change across our landscape, which is vital information for developing effective conservation plans. It also highlights concerns about forest-associated species in this region—the need to balance timber harvest, a mixed-severity fire regime, and endangered species management continue to present complex conservation challenges.”

“We have been so lucky to consistently get awesome field crews—we host six to ten interns each year, and they travel all over the Klamath-Siskiyou bioregion, camping regularly throughout the field season. We have had interns from more than seventeen different countries, and they all receive extensive training and work very hard,” adds Rockwell. “This work is so important. We need robust baseline data if we are going to be aware of any kind of population change, let alone be able to do something about it!”

Spatial variation in songbird demographic trends from a regional network of banding stations in the Pacific Northwest is available at http://www.bioone.org/doi/full/10.1650/CONDOR-17-44.1.

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, 2.654.

About Klamath Bird Observatory: Based in Ashland, Oregon, KBO is a scientific non-profit organization that achieves bird conservation in the Pacific Northwest and throughout the migratory ranges of the birds of our region. Emphasizing high caliber science and the role of birds as indicators of the health of the land, KBO specializes in cost-effective bird monitoring and research projects that improve natural resource management. Also, recognizing that conservation occurs across many fronts, we nurture a conservation ethic in our communities through our outreach and educational programs.

A First Look at Geographic Variation in Gentoo Penguin Calls

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A calling Gentoo Penguin. Photo credit: M. Lynch

Vocal communication is central to the lives of many birds, which use sound to attract mates and defend territories. Penguins are no exception, but we know little about how or why penguin vocalizations vary geographically between isolated populations. A new study from The Auk: Ornithological Advances takes a broad look at vocalizations across the range of Gentoo Penguins and concludes that while their calls do vary from place to place, we still have a lot to learn about the processes at work.

The Gentoo Penguin’s “ecstatic” call, consisting of repeated pairs of short syllables, is used to attract and contact mates. Maureen Lynch and her PhD advisor Dr. Heather Lynch (no relation) of Stony Brook University recorded ecstatic calls at 22 Gentoo Penguin colonies across the Antarctic Peninsula, southern Argentina, and nearby islands. While they found variation in call frequency and duration both within and between colonies, no clear patterns emerged based on latitude, region, or subspecies. An algorithm based on their data was able to classify calls to correct colonies better than random, but with a high error rate.

Their results suggest that the vocal characteristics of colonies drift independently of each other over time. Within colonies, it may be beneficial for individuals to differ in their calls so that they can tell each other apart. “There is so much that we still do not know about penguin vocal behavior,” says Heather. “We see this as being very much the beginning, rather than the end, of understanding how penguins communicate, how and if such communications play a functional role in protection against predators, choice of mates, and breeding site selection.”

“Work in the Antarctic is always challenging, and this project was time- and data-intensive, with data collection over three field seasons,” adds Maureen. “Unexpected challenges came from flying birds rather than penguins. The recording units hold up well in the Antarctic elements and can even record over winter, but I learned the hard way that if I leave a Song Meter unattended in the Falkland Islands, the Striated Caracaras will eat the windscreens off the microphones and can actually pull the microphones off.”

“Understanding the drivers of population differentiation is increasingly important for species such as penguins that are being impacted by climate change,” according to Fordham University’s J. Alan Clark, a penguin behavior researcher who was not involved in the study. “This study, the largest of its kind, takes a creative and rigorous approach to exploring the role of vocalizations in population differentiation across a wide geographic range and across populations with known intraspecific genetic variation. The results of this study provide practical insights that help set the stage for future research on interactions between speciation processes and climate change.”

Variation in the ecstatic display call of the Gentoo Penguin (Pygoscelis papua) across regional geographic scales is available at http://www.bioone.org/doi/full/10.1642/AUK-17-4.1.

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.

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Could Condors Return to Northern California?

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A study of lead exposure indicates condors could one day return to Northern California. Image credit: C. West

In 2003, Northern California’s Yurok Tribe initiated efforts to reintroduce California Condors on their lands. While wild condors have not existed in the region for more than a hundred years, a new study from The Condor: Ornithological Applications suggests that hunters transitioning from lead to non-lead ammunition may allow these apex scavengers to succeed there once again.

Lead, which condors consume when scavenging at carcasses of animals killed with lead ammunition, is the main factor limiting their recovery; lead toxicosis was responsible for 26% of juvenile condor deaths and 67% of adult condor deaths between 1992 and 2009. To assess condor’s prospects in Northern California, Chris West of the Yurok Tribe Wildlife Program and his colleagues trapped two other avian scavengers, Turkey Vultures and Common Ravens, at nine sites in the region between 2009 and 2013. Collecting blood samples from 137 vultures and 27 ravens, they found that lead levels in ravens were almost six times higher during hunting season, when they were exposed to animal remains tainted with lead ammunition, than the rest of the year. Vulture’s migratory movements meant they couldn’t be sampled across seasons, but older vultures tended to have higher concentrations of lead, suggesting that older, more dominant individuals exclude younger birds from foraging on carcasses.

While this may sound like bad news, it means little stands in the way of condor recovery if hunters shift away from using lead ammunition in the region. A statewide ban on lead ammunition in California takes effect in 2019, and West and his colleagues are optimistic that it may lower lead exposure to scavengers if it includes outreach programs to help the state’s hunting community through the transition. “Our hopes for condor reintroduction to our area and recovery overall is very high. We are currently going through the National Environmental Policy Act (NEPA) process to select release locations and assess and mitigate impacts to land owners and managers in the region,” says West. “The return of condors to the Pacific Northwest, after more than a century-long absence, will be a testament to the ability of federal, tribal, state, and private entities to come together to champion the cause of wildlife, ecosystem, and cultural recovery in our region.”

“Northern California still has viable habitat for free-flying California Condors, and these results suggest it is possible to succeed in this region, particularly as a broader switch from lead to non-lead ammunition use is realized,” adds to Kelly Sorenson, Executive Director of the Ventana Wildlife Society and an expert on condor recovery who was not involved in the study. “If we fix the lead problem, condors should survive in the wild again without the assistance of people, whether in Northern California or other suitable locations where they are being released.”

Feasibility of California Condor recovery in northern California, USA: Contaminants in surrogate Turkey Vultures and Common Ravens is available at http://www.bioone.org/doi/abs/10.1650/CONDOR-17-48.1.

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. The Condor had the top impact factor among ornithology journals for 2016.

Social Environment Matters for Duck Penis Size

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Penis size in Ruddy Ducks has a complex relationship with the birds’ social environment. Image credit: P. Brennan

Most birds lack genitalia, but male ducks are known for their long, spiraling penises, which have evolved through an ongoing cat-and-mouse game with females. A new study from The Auk: Ornithological Advances looks at whether these impressive organs are affected by the social environment—that is, whether male ducks that face more competition grow bigger penises. While this appears to be true for some species, in others the relationship between social environment and penis growth is more complex.

Patricia Brennan of Mount Holyoke College and her colleagues tested their hypothesis in two species: Ruddy Ducks, which are very promiscuous, do not form pair bonds, and have relatively long penises, and Lesser Scaup, which form seasonal pair bonds and have relatively short penises. Keeping captive ducks in either pairs or groups during the breeding season over two years, they found that Lesser Scaup had longer penises on average when housed in groups with other males, as predicted. For Ruddy Ducks, the effects were more complicated—many males failed to reach sexual maturity until the second year of the experiment, and when they did, the smaller Ruddy Duck males housed in groups grew their penises faster than males housed in pairs, but grew out of sync with each other and stayed in reproductive condition for only short periods of time.

Small Ruddy Ducks males faced with intense competition may strategically offset their development from each other to reduce the costs of male–male aggression and make the best of a bad situation. Additionally, since Ruddy Ducks already have relatively long penises on average compared to other waterfowl species, their ability to grow even larger based on social cues may be limited. In any case, the study shows that the level of competition that individual male ducks experience can have a big effect on their genitals.

The biggest challenge during the study, says Brennan, wasn’t measuring the ducks—it was simply keeping them housed and fed. “Keeping ducks in captivity is expensive,” says Brennan. “We were lucky to partner with the Livingstone Ripley Waterfowl Conservancy in Litchfield, Connecticut, where their expert personnel kept the ducks healthy and in beautiful, naturalistic enclosures year-round.”

“This is an excellent experimental study of penis morphology, looking at the effects of social environment on penis size in two duck species that have different mating systems,” according to Queen’s University’s Bob Montgomerie, an expert on reproductive strategies who was not involved in the study. “The question now is whether the observed increase in penis size in Lesser Scaup under the threat of sperm competition actually gives males a competitive advantage. Like all good studies, this one will undoubtedly stimulate more research, as it provides both methodologies and a clear focus on interesting questions.”

Evidence of phenotypic plasticity of penis morphology and delayed reproductive maturation in response to male competition in waterfowl is available at http://www.bioone.org/doi/full/10.1642/AUK-17-114.1.

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.

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Song Experiments Reveal 21 Possible New Tropical Bird Species

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Playback studies indicate that two populations of Buff-throated Foliage-gleaners do not recognize each other’s songs. Photo credit: B. van Doren

Birds often choose their mates based on song, making it a key factor in separating species. However, analyzing spectrograms can only tell us so much—the characteristics that birds hone in on when identifying potential mates may not be the same ones scientists notice in audio recordings. A new study from The Auk: Ornithological Advances uses field experiments to “ask the birds themselves” and uncovers as many as 21 previously unrecognized species.

Benjamin Freeman of the University of British Columbia and Graham Montgomery of Cornell University compared these two methods—analysis in the lab and experiments in the field—for 72 pairs of related but geographically separated bird populations in Costa Rica, Panama, and Ecuador. In addition to analyzing more than a thousand song recordings for seven variables, they used playback experiments to test birds’ real-world reactions to recordings of their relatives, observing whether or not they approached the speaker. Their results show that when the divergence between the characteristics of the recordings is high, birds consistently fail to recognize recordings of their relatives in the field, but when divergence is low, birds’ discrimination is much less consistent. In other words, analyzing recordings can’t accurately predict how birds will act when presented with songs just slightly different from their own.

Many pairs that failed to recognize each other are currently categorized as members of the same species, suggesting that current taxonomy does not reflect actual bird behavior when it comes to song. Freeman and Montgomery propose that 21 such pairs should be recognized as separate species based on song discrimination and that playback experiments should be the standard for assessing whether song divergence between populations is a barrier to interbreeding. “It is abundantly clear to anyone familiar with the amazing diversity of Neotropical birds that there are many cases where populations that sing very different songs are classified as the same species,” says Freeman. “These populations look the same—they have similar plumage and are similar in size and shape—but assuming that populations that sing differently tend not to interbreed, this means that species-level diversity in the Neotropics is underestimated.”

“Playback experiments between geographically isolated taxa provide key data on how populations might perceive each other in terms of ‘same’ or ‘different’ if they were in actual contact,” according to Louisiana State University’s J.V. Remsen, an expert on Neotropical birds who was not involved in the research. “Hopefully, this pioneering study will catalyze a wave of similar studies around the globe as a way to approach the always-thorny problem of species limits in these birds.”

Using song playback experiments to measure species recognition between geographically isolated populations: A comparison with acoustic trait analyses is available at http://www.bioone.org/doi/full/10.1642/AUK-17-63.1.

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.

Will Mallards Hybridize Their Cousins out of Existence?

Mallard - Gary Kramer, USFWS, public domain

Mallards may threaten their relatives’ genetic distinctiveness through hybridization. Photo credit: Gary Kramer, USFWS (public domain)

Mallards—the familiar green-headed ducks of city parks—are one of a group of closely related waterfowl species, many of which are far less common. Interbreeding with Mallards can threaten the genetic distinctiveness of those other species and cause concern for their conservation. A new study from The Condor: Ornithological Applications investigates hybridization between Mallards and Mottled Ducks, a species specially adapted for life in Gulf Coast marshes, and finds that while hybridization rates are currently low, human activity could cause them to rise in the future.

In Florida, hybridization between domesticated Mallards and Mottled Ducks is a cause for concern, but the degree of hybridization in the western Gulf Coast region is less well known. Louisiana State University’s Robert Ford and his colleagues took blood samples from Mottled Ducks captured on the coast of Louisiana in 2011–2014, supplementing them with samples from Mottled Ducks and Mallards from Texas, Alabama, and Mississippi. Analyzing the birds’ DNA, they found that the hybridization rate in the western Gulf Coast region is currently only 5–8%, a level lower than what’s been documented in Florida. However, that doesn’t mean the western Gulf population is completely in the clear.

Currently, the two species have little opportunity to interact in the region during the breeding season; Mottled Ducks nest in coastal marshes, while most Mallards are migratory and breed outside the region. However, the ongoing loss of marsh habitat could cause Mottled Ducks to move into urban and suburban areas, where they will be more likely to encounter resident Mallards. To prevent future problems, Ford and his colleagues recommend ongoing monitoring of hybridization in the region and better protection of coastal marsh habitat.

“The biggest challenge in collecting samples was finding molting Mottled Ducks, which we collected during bird banding operations in the summer. Identifying birds as either Mottled Ducks or Mallards in the summer can be difficult, but most of our banders had years of experience and we did not have many problems,” says Ford. “In the future, I would like to see improvements in the methods to identify hybrids, such as more precise techniques that could identify gene combinations unique to hybrids.”

“Hybridization between Mottled Ducks and Mallards is a significant conservation concern in the southern U.S.,” according to waterfowl expert and Auburn University emeritus professor Gary Hepp, who was not involved in the study. “Ford et al. recommend programs to monitor future changes in hybridization, and a proactive management approach similar to Florida’s that controls the number of non-migratory Mallards while prohibiting future releases of game farm Mallards may also be prudent.”

Hybridization between Mottled Ducks (Anas fulvigula maculosa) and Mallards (A. platyrhynchos) in the western Gulf Coast region is available at http://www.bioone.org/doi/abs/10.1650/CONDOR-17-18.1.

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.