AUTHOR BLOG: To the Grasshopper Sparrow, the Grass May Be Greener on the Other Side

Emily Williams

Linked paper: Patterns and correlates of within-season breeding dispersal: A common strategy in a declining grassland songbird by E.J. Williams and W.A. Boyle, The Auk: Ornithological Advances 135:1, January 2018.

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SY-GD, or silver-yellow, green-dark blue, is a male fiercely defending his territory on his favored signpost perch. Photo credit: D. Rintoul

Late in the summer of 2013, when Alice Boyle, a new faculty member at Kansas State University, was embarking on studies of grassland birds at the Konza Prairie Biological Station in northeastern Kansas, she noticed something really curious: Individual Grasshopper Sparrows she had color-banded earlier in the season were suddenly popping up in new places, singing their hearts out in locations far from where they were originally captured. Whether this was a weird one-off or a predictable and common behavior of grassland birds, Boyle didn’t know.

I started at Kansas State University as Alice’s first graduate student the next fall. She told me the story of the Grasshopper Sparrows and the strange things they did over the summer. With my fondness for movement ecology and a taste for novelty, I opted to base my master’s thesis on the rogue Grasshopper Sparrows seeking greener pastures.

To rewind a little bit, I should explain why this kind of behavior was surprising. The Grasshopper Sparrow is a small, grassland-obligate migratory songbird that spends its winters along the Gulf Coast and Northern Mexico and travels to the Great Plains to spend its summers. Migration is energetically costly, requiring a lot of time and preparation. Once birds arrive at breeding grounds, they have a relatively short window of time to set up a territory, find a mate, build a nest, raise young, and feed fledglings, and then undergo molt, feed, and prepare for the long journey back to the wintering grounds. All of this has to be accomplished in a span of a few short months. Given the constraints of time, resources, and energy, you’d think that they would stick pretty close to their original territory for the whole breeding season. That is what most migrant birds do, after all. The fact that Grasshopper Sparrows would switch territories, duplicating their efforts of setting up another territory, finding a potential new mate, and trying to nest again—it seems like it wouldn’t be worth it. The fact that Grasshopper Sparrows are indeed doing this—changing territories once, twice, maybe three times, even—makes them apparently unusual compared to their migratory counterparts and begs the question, why go to all that effort?!

Before we could examine why Grasshopper Sparrows move around during the breeding season, we first needed to determine just how common this kind of behavior was. We also wanted to find out the distances over which they traveled, where were the new places they chose to settle, and how frequently they moved locations. Following that initial season in 2013, we set out to answer these questions and looked for this behavior in full force. In the next three seasons of field work, we banded 779 Grasshopper Sparrows, outfitted 19 individuals with radio-transmitters to follow their movements, and searched for color banded birds throughout our study area every week to keep track of territory holders and their whereabouts throughout the season.

What we found, we couldn’t have predicted: Within-season breeding dispersal behavior in Grasshopper Sparrows was way more common than we expected. Depending on which of the different metrics we calculated, between 33% and 75% of males disperse at least once within a single breeding season. The scale of movement between territory locations was also remarkable; one individual moved 9 km between breeding attempts—a movement considered pretty large to a bird that defends an average territory size of 43 meters in diameter! If we had not been systematically looking for this behavior, we might have easily missed it; in many areas, densities of Grasshopper Sparrows remained constant throughout the breeding season, but the identities of territory holders changed, sometimes more than once over the summer.

The fact that these birds are moving around a lot during the breeding season introduces its own list of new questions. Now that we detailed the patterns of this behavior, we could begin to answer the questions of why. Why do they do this? What determines why some leave, and some stay? And what determines where they settle next? Could this be a common strategy of other birds occupying similar habitats?  While trying to determine whether this movement was truly unusual by digging into the literature, I actually found quite a bit of evidence for such movements. While the terminology is not consistent, it seems that within-season breeding dispersal could be more common in grassland birds than elsewhere.

The answers to some of these questions formed the rest of my MS research, and some remain as ones we are still working on. But now that the first piece of the puzzle is in place, the next steps are to explore the evolutionary and ecological causes of within-season breeding dispersal in such an interesting little brown job.

To find out more regarding this Grasshopper Sparrow movement story, visit aliceboyle.net and follow us on social media.

Emily on Twitter: twitter.com/wayfaringwilly

Alice on Twitter: twitter.com/birdfiddler

Youtube channel: youtube.com/channel/UCiQiNb9syQ5F455XielMjDA

Flickr: flickr.com/photos/141805443@N08/

Grassland Sparrows Constantly Searching for a Nicer Home

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A Grasshopper Sparrow with a radio transmitter. Photo credit: E. Williams

Some birds regularly move to new territories between years, depending on factors including habitat quality and the presence of predators, but what about within a single breeding season? Grassland ecosystems are particularly dynamic, continuously shaped by fire and grazing, and a new study from The Auk: Ornithological Advances confirms that one particular grassland bird moves frequently each summer in search of the best territories. For Grasshopper Sparrows, the grass really does look greener on the other side.

Emily Williams and Alice Boyle of Kansas State University captured 647 male Grasshopper Sparrows over the course of three breeding seasons and marked them with identifying color bands, surveying territories weekly to track their movements. The results indicate that about 75% of males changed territories at least once per season, with a third of banded defending new territories at least 100 meters away from where they were originally sighted. Additionally, 9 of 19 birds fitted with radio transmitters established new territories as far as 1200 meters away from their original locations.

“We had many plots where the density remained relatively stable over the entire breeding season, which could appear as if individual birds remained settled in the same areas over time. However, what we found was the complete opposite—individuals were blinking in and out of territories the entire time,” says Williams, who has since moved on to a position at Denali National Park and Preserve. “So while an onlooker could see a male Grasshopper Sparrow singing on a single patch of ironweed for months at a time, the identity of the individual claiming that ironweed as his own could change two or three times in a single summer.” Without careful observations, researchers could completely miss these dynamic movements happening over the course of a season.

This high turnover implies that while some birds might perceive a patch of habitat as no longer suitable, others see the same area as a good place to settle, perhaps because they base decisions on their individual experiences of nest success or failure. High mobility may benefit grassland birds by helping them locate isolated patches of high-quality habitat and colonize newly created or restored habitat, but could also challenge researchers’ ability to accurately track survival over time.

“Many avian ecologists have probably anecdotally noticed within-season shifts in breeding territories, yet this is one of the first attempts to actually quantify this phenomenon. The extent to which territorial turnover occurred and the fairly extensive distances moved by males within a season are intriguing!” says the University of Wyoming’s Anna Chalfoun, an expert on grassland birds who was not involved in the study. “I am left wondering if this behavior is more common than ornithologists have previously acknowledged and what drives proximate shifts in breeding territories. The results certainly have implications for habitat management for territorial birds of concern and for the accuracy of survival and site fidelity analyses.”

Patterns and correlates of within-season breeding dispersal: A common strategy in a declining grassland songbird is available at http://www.bioone.org/doi/full/10.1642/AUK-17-69.1.

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.

Safety, Not Food, Entices Geese to Cities

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Radio transmitter data has revealed the real reason geese hang out in cities. Photo credit: M. Horath

Canada Geese have shifted their winter range northward in recent years by taking advantage of conditions in urban areas—but what specific features of cities make this possible? A new study from The Condor: Ornithological Applications suggests that rather than food, geese are seeking safety, congregating in areas where they can avoid hunters and be buffered from the coldest winter temperatures.

Heath Hagy of the University of Illinois at Urbana–Champaign and his colleagues captured 41 geese in the Greater Chicago Metropolitan Area between 2014 and 2016 and fitted them with radio transmitters to track their movements. While the geese used a remarkable variety of urban habitats, they preferred deep water and rivers over green space such as parks when temperatures dropped enough to tax their ability to maintain their body temperature. For geese that remained within the metropolitan area, winter survival was 100%, but this dropped to 48% for those that emigrated out to forage in surrounding agricultural fields, countering expectations that the proximity of agricultural habitat may be a factor in geese’s winter expansion in the area. Together, these results suggest that sanctuary may be a higher priority for wintering geese than good foraging habitat.

Better understanding how geese use urban habitat in winter may help reduce human–wildlife conflicts such as collisions with airplanes. “The growth of urban areas and northward expansion of row-crop agriculture have changed the way geese migrate. Unfortunately, some of our large cities have become goose sanctuaries, where resident geese and migratory geese congregate during winter to escape hunting pressure,” says Hagy. “Although additional research is needed, our data will be useful to guide goose harassment efforts, which may offset the benefits of remaining inside urban areas during winter and open hunting seasons.”

“This work offers comprehensive insights into the biology and behavior of a large wintering population of Canada geese that inhabits a major metropolitan area in the mid-western U.S. Appropriately grounded in an energetic context, the study thoroughly describes how Canada geese utilize the urban environment under varying weather conditions and demonstrates the survival benefits of urban adaptation,” according to The Ohio State University’s Robert Gates, a wildlife management expert who was not involved in the research. “Findings from this study provide a firm biological grounding for the development and implementation of management actions to alleviate human–Canada goose conflicts in urban areas.”

Survival and habitat selection of Canada Geese during autumn and winter in metropolitan Chicago, USA is available at http://www.bioone.org/doi/abs/10.1650/CONDOR-16-234.1.

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.

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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.