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.

Invasive Frogs Give Invasive Birds a Boost in Hawaii

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Invasive coqui frogs are affecting nonnative bird populations in Hawaii. Photo credit: R. Choi

Puerto Rican coqui frogs were accidentally introduced to Hawaii in the 1980s, and today there are as many as 91,000 frogs per hectare in some locations. What does that mean for native wildlife? Concerns that ravenous coquis could reduce the food available for the islands’ native insect-eating birds, many of which are already declining, spurred researchers to examine the relationship between frog and bird populations—but their results, published in The Condor: Ornithological Applications, weren’t what they expected.

Working at fifteen sites on the island of Hawaii in 2014, Utah State University’s Robyn Smith, Karen Beard, and David Koons determined whether coquis were present at each site by listening for their calls at night and then estimated coqui density in invaded plots through a visual search.  Bird surveys at all sites recorded 20 species, of which only 5 were native. To the researchers’ surprise, native birds showed no response to coqui density or presence, but three of the nonnative species were more abundant in plots with coqui. The overall abundance of nonnative birds ranged from an average of 57 birds in coqui-free plots up to 97 where coqui density was highest.

Coquis forage mostly in leaf litter, while Hawaii’s native insect-eating birds forage mostly in canopy and understory, so perhaps they aren’t in direct competition for insects. Nonnative birds may be getting a boost directly by eating adult or juvenile coquis, or indirectly through coqui’s effects on the ecosystem—coquis may alter nutrient cycling and even increase fly populations thanks to the extra biomass their excrement and carcasses create. “I was very surprised with the results for birds. It had been hypothesized before our study that coquis would compete with birds, particularly natives, because we know that coquis reduce insects where they invade,” says Beard. “In retrospect, I guess it’s not too surprising that predation is a more important interaction than competition—that is a common finding in invaded systems—but it was definitely not what we went in to test. The response that we see for Common Mynas and Red-billed Leiothrix is pretty convincing. We’re pretty sure that some of this increase is due to these species eating live or dead coquis, and we’re suggesting that some non-native birds are likely consuming coquis and this novel resource appears to be increasing their populations.”

“The findings presented in the study by Smith, Beard, and Koons, where abundances of some species of non-native birds in Hawaii are correlated with invasive coqui frogs, are very intriguing,” according to the USDA’s Aaron Shiels, an expert on invasive species in island ecosystems. “Furthermore, their interesting findings beg for future experimental manipulations that would uncover the causal factors that explain the patterns that they have observed.”

Invasive coqui frogs are associated with greater abundances of nonnative birds in Hawaii, USA is available at http://www.bioone.org/doi/full/10.1650/CONDOR-17-109.1.

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.

Penguins’ Calls Are Influenced by Their Habitat

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Variation in Little Penguins’ agonistic calls appears to be driven by the habitats where they live. Photo credit: D. Colombelli-Négrel

Birds use vocalizations to attract mates, defend territories, and recognize fellow members of their species. But while we know a lot about how variations in vocalizations play out between populations of songbirds, it’s far less clear how this variation affects birds such as penguins in which calls are inherited. A new study from The Auk: Ornithological Advances examines differences in the calls of Little Penguins from four colonies in Australia—nocturnal birds for whom vocalizations are more important that visual signals—and finds that disparities in habitat, rather than geographic isolation or other factors, seem to be the key driver of variation in the sounds these birds use to communicate.

Diane Colombelli-Négrel and Rachel Smale of Australia’s Flinders University recorded calls from four Little Penguin populations across a small area of South Australia, one of which had previously been shown to have subtle genetic differences from the other three, and used playback experiments to test penguins’ ability to distinguish between calls from different colonies. They found that agonistic calls, which are used in pair displays and aggressive situations, varied among the four populations, and that the calls’ characteristics appeared to depend on small-scale differences in the habitat where the penguins lived. However, birds did not discriminate between calls originating from different colonies, which suggests that agonistic calls don’t seem to play a role in isolating the two different genetic groups.

Penguins breeding in open habitats produced lower-frequency calls than those breeding in habitats with denser vegetation—the opposite of the trend typically observed in songbirds. The authors speculate that agonistic calls may be subject to different selective pressures because they’re used in close encounters with other birds rather than to communicate across distances, and could also be influenced by variation in the noise level of wind and surf. “I was excited to find that calls were influenced by habitat, as this hasn’t been investigated much in seabirds and most of our knowledge in this area comes from studies on songbirds,” says Colombelli-Négrel. “This new research suggests that many factors influence call variation in birds, which also depends on the function of the calls. This study highlights that many questions remain and that studies need to investigate more than one factor in conjunction with the function of the calls to fully understand call variation in seabirds.”

“This work tells an interesting story of vocal diversification in Little Penguins, and gives insight into how individual and micro-scale variation effects behavior,” according to Stony Brook University’s Heather Lynch, an expert on penguin calls who was not involved in the study. “Non-vocal-learning birds are relatively understudied in terms of vocalizations, and it is great to see penguin vocalizations being studied in such a way.”

Habitat explained microgeographic variation in Little Penguin agonistic calls is available at http://www.bioone.org/doi/full/10.1642/AUK-17-75.1.

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.

Translocated Hawks Thrive in Hispaniola

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A Ridgway’s Hawk on the island of Hispaniola. Photo credit: R. Thorstrom

Species translocation—capturing animals in one place and releasing them in another—is a widely used conservation method for establishing or reestablishing populations of threatened species. However, translocation projects often fail when the transplanted animals fail to thrive in their new home. A new study from The Condor: Ornithological Applications demonstrates how close monitoring of the animals being released into a new area is helping wildlife managers gauge the success of their effort to save the Ridgway’s Hawk of Hispaniola.

Ridgway’s Hawk is a critically endangered raptor endemic to the Caribbean island of Hispaniola. Since 2009, the Peregrine Fund has translocated 104 nestlings from the species’ stronghold in a national park to a protected resort area called Punta Cana 130 kilometers away. They monitored the birds after their release, tracking their survival and breeding success, as well as collecting the same data on 36–110 breeding pairs per year in the original national park population. Survival rates were high in both locations, and more young hawks began breeding on the resort property, probably because more territories were available due to the birds’ low numbers.

Lead author Chris McClure of the Peregrine Fund and his colleagues believe that the “soft release” method they use with the translocated birds, involving an adjustment period where young birds are allowed to come and go freely but are provided with food, has contributed to the success of the project. Post-release monitoring has been a valuable tool for gauging their success and planning future conservation efforts, and they hope that more wildlife managers will consider incorporating this into their plans when seeking funding for translocation projects. “Our results show that the new population of Ridgway’s Hawks in Punta Cana is taking hold, but we only know that because of the hard work of our staff and volunteers in tracking these birds,” says McClure. “I think our study is a great example of monitoring to ensure that conservation goals are actually achieved.”

“The paper is a good example of the important role of post-release monitoring in translocation projects,” adds Massey University’s Doug Armstrong, an expert on reintroduction programs who was not involved in the study. “It is easy for people to invest a lot of effort into well-meaning but ineffectual translocations projects if they aren’t monitored. This paper illustrates how state-of-the-art methods can be applied to provide clear and useful information of post-release survival and recruitment.”

Successful enhancement of Ridgway’s Hawk populations through recruitment of translocated birds is available at http://www.bioone.org/doi/full/10.1650/CONDOR-17-77.1.

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.

How Many Golden Eagles Are There?

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Photo credit: D. Brandes

For conservation efforts to be effective, wildlife managers need to know how many individuals of a species are out there. When species are spread out over large areas and occur at low densities, as is the case with the Golden Eagle, figuring this out can be tricky. However, a new study from The Condor: Ornithological Applications applies an old technique called “mark-recapture” in a novel way, eliminating the need to actually capture and mark eagles but instead, using math that allows scientists to turn individual observations into population estimates.

West Virginia University’s Andrew Dennhardt, Adam Duerr, and Todd Katzner and Lafayette College’s David Brandes used observations made by volunteer “citizen-scientists” of Golden Eagles migrating along a single, long mountain ridgeline in Pennsylvania to estimate the total number of eagles passing through the area each year. To do this, they developed a new way to apply a classic ecology tool called mark-recapture analysis—capturing and marking a portion of a population, and then counting the number of marked individuals in another group captured later. Helped by the fact that observers were often able to categorize individual eagles as either immature or adult birds, the scientists were able to identify instances of individual eagles being sighted at more than one location as they made their way south along the ridge over the course of a day, treating these subsequent sightings as “recaptures.”

Volunteers reported more than 3,000 sightings of Golden Eagles at five count sites along the ridge from 2002 to 2011. The analysis used in the study, which lets researchers estimate how many birds were missed as well as how many were seen more than once, suggests that these sightings represented between 2,592 and 2,775 individual eagles over the ten year period, with approximately 1,300 passing through the area on average in a given year. Past studies indicate that the total population of eagles breeding in Quebec and migrating through Pennsylvania is around 5,000, making this about a quarter of the larger population. Because the eagles are difficult to count on their breeding grounds, however, better methods for tracking their numbers during migration represent a significant advance.

“Conservation of Golden Eagles in eastern North America is a really important goal for lots of reasons—it is a small, historically declining population, at risk from anthropogenic threats and habitat loss. A central part of that conservation goal is figuring out how many of the darn things there are. Andrew’s work is the first empirical estimate of golden eagle population size,” says Katzner, now a Research Wildlife Biologist at the US Geological Survey. “Nothing quite like this has ever been done. We’ve taken a standard tool, mark–recapture, and turned it on its head to give us a new way to estimate population size.”

“For me, this was a dream come true, because I got to work on a project relevant to the conservation of the species that originally inspired me to enter the field of wildlife ecology and management,” says Dennhardt, now at Michigan State University. “Partnerships between researchers and citizen-scientists can help improve wildlife management decisions to address threats to migratory Golden Eagles and other species. I hope this work inspires future researchers to evaluate the populations of other migratory species, and that it encourages the greater scientific community to consider new and existing citizen-science programs and think about how such programs’ data might be used in their own research toward improving resource management and decision making.”

Applying citizen-science data and mark–recapture models to estimate numbers of migrant Golden Eagles in an Important Bird Area in eastern North America is available at http://www.bioone.org/doi/full/10.1650/CONDOR-16-166.1.

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.

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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