2016 Journal Impact Factors Released

The 2016 impact factors for peer-reviewed journals were released last week, and both journals published by the American Ornithological Society saw a boost in their numbers—The Condor is up to 2.654 from 1.427 and is now #1 of the 24 ornithology journals ranked, and The Auk is up to 2.096 from 1.871 (ranking #4). This means that the American Ornithological Society now publishes half of the top four ornithology journals in the world.

Impact factors are calculated based on the number of citations received in a year by articles published in a journal during the two preceding years and are considered to be an important measure of a journal’s prominence in its field. The AOS publications team wants to thank all of our Associate Editors, authors, and reviewers, as well as everyone who reads and cites The Auk and The Condor!


Muscle Fibers Alone Can’t Explain Sex Differences in Bird Song

Male birds tend to be better singers than females—but does the basis for this difference lie in the brain or in the syrinx, the bird equivalent of our larynx? The researchers behind a new study from The Auk: Ornithological Advances analyzed the muscle fibers in the syrinxes of male and female birds from a range of species and found, to their surprise, that the amount of “superfast” muscle wasn’t typically related to differences in vocal ability between the sexes.

Most muscle fibers are one of two types—fast, specialized for short, intense bursts of activity, or slow, specialized for endurance. However, some animals, including birds, have a third type called superfast muscle that can contract around 200 times per second. Ron Meyers of Weber State University and his colleagues hypothesized that superfast muscle fibers in the syrinx might explain the greater singing ability of male birds, but when they analyzed the syringeal muscles of male and female birds from a range of species, they found that the amount of superfast muscle fiber didn’t differ between the sexes in most species. Instead, their results suggest that the role of superfast muscle is more complicated than they expected and may be related to the entire range of vocalizations of a species rather than song alone. Even though females of some species don’t sing, their superfast muscle fibers appear likely to play a role in the calls they use for other types of communication.

The researchers collected syringeal tissue from a total of ten bird species, some wild-caught and some from a University of Utah aviary. All species had both fast muscle and superfast muscle fiber in their syrinxes, but there was a clear sex difference in fiber type composition in only two species studied, Bengalese Finches and Zebra Finches. Based on this, the researchers speculate that the need for superfast muscle may be related to the entire vocal repertoire of each sex, not just singing behavior. Calls made by Zebra Finch females don’t have acoustic features that would require rapid muscle control, but in other species females may produce calls that require the muscle control provided by superfast fibers even if they don’t sing.

“The data really surprised us,” says Meyers. “Based on our first species studied, starlings and Zebra Finches, we went into this thinking that superfast fibers were related to singing in males. Zebra Finch males sing and females don’t, and males have 85% of the syrinx muscles made up of superfast fibers. In starlings, both male and females sing, and they both had about a 65% make-up of superfast fibers. But as the number of species we looked at grew, we had to totally change our perception of the role of superfast fibers in singing and the role they actually play in vocalizing.”

“Most of the research investigating the mechanisms of bird song focuses on the brain. However, research has begun to suggest that peripheral structures like the syrinx influence song divergence, which of course is an important factor that contributes to avian biodiversity,” according to Wake Forest University’s Matthew Fuxjager, an expert on superfast muscle. “This study therefore provides an exciting starting point to address this issue from a physiological perspective, and it shows that muscle fiber content in the syrinx might not be a strong predictor of avian vocal diversity. But then what is? I would argue that we’re still working this out, and that this study will provide an intriguing framework from which more work in this area can be conducted.”

Is sexual dimorphism in singing behavior related to syringeal muscle composition? is available at http://www.bioone.org/doi/full/10.1642/AUK-17-3.1.

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.

Which Extinct Ducks Could Fly?

AUK-17-23 J Watanabe

Fossils of extinct ducks and geese provide new clues about flightlessness. Photo credit: J. Watanabe

We’re all familiar with flightless birds: ostriches, emus, penguins—and ducks? Ducks and geese, part of a bird family called the anatids, have been especially prone to becoming flightless over the course of evolutionary history. However, it can be difficult to determine from fossils whether an extinct anatid species could fly or not. A new study from The Auk: Ornithological Advances takes a fresh approach, classifying species as flightless or not based on how far their skeletal proportions deviate from the expected anatomy of a flying bird and offering a glimpse into the lives of these extinct waterfowl.

Kyoto University’s Junya Watanabe painstakingly measured 787 individual birds representing 103 modern duck and goose species. From this data, he developed a mathematical model that was able to separate flightless and flying species based on their wing and leg bones—flightless species, the math confirmed, have relatively small wings and relatively large legs. Applying the model to fossil specimens from 16 extinct species identified 5 of the species as flightless, ranging from a land-dwelling duck from New Zealand to a South American duck that propelled itself underwater with its feet.

“I really enjoyed measuring bones in museums and appreciate the hospitality given to me by museum staff. One of the most exciting things was to find interesting fossils that were previously unidentified in museum drawers,” says Watanabe. “What is interesting in fossil flightless anatids is their great diversity; they inhabited remote islands and continental margins, some of them were specialized for underwater diving and others for grazing, and some were rather gigantic while others were diminutive.”

“Dr. Watanabe has developed a valuable statistical tool for evaluating whether a bird was capable of powered flight or not, based on measurements of the lengths of only four different long bones. His method at present applies to waterfowl, but it could be extended to other bird groups like the rails,” according to Helen James, Curator of Birds at the Smithsonian Institution’s National Museum of Natural History. “Other researchers will appreciate that he offers a way to assess limb proportions even in fossil species where the bones of individual birds have become disassociated from each other. Disassociation of skeletons in fossil sites has been a persistent barrier to these types of sophisticated statistical analyses, and Dr. Watanabe has taken an important step towards overcoming that problem.”

Quantitative discrimination of flightlessness in fossil Anatidae from skeletal proportions is available at http://americanornithologypubs.org/doi/full/10.1642/AUK-17-23.1.

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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AUTHOR BLOG: ‘Bare Parts’ are an Important but Underappreciated Avian Signal


Two female American Goldfinches in an antagonistic interaction. Bill-color, derived from carotenoids, is a signal of dominance among female goldfinches but not among males. Image credit: K. Tarvin

Erik Iverson

Linked paper: The role of bare parts in avian signaling by E.K. Iverson and J. Karubian, The Auk: Ornithological Advances 134:3, July 2017.

Birds are well-known for being among the most colorful of all animals, with many species displaying striking, brightly-colored feathers. Scientists have long wondered why color is so important to fitness, and hundreds of studies have been published on the relationships between plumage and traits such as age, physiological condition, reproductive success, and attractiveness to mates. However, there is a growing awareness that plumage is not the only important site of coloration among birds; there is also considerable variation within and between species in the color of bills and in bare skin such as legs, feet, ceres, or wattles. Yet compared to plumage, these ‘bare part’ ornaments have received relatively little attention; a 2006 review of carotenoid coloration in birds, for instance, identified only 14 studies of bare parts versus 130 studies of plumage.

Unlike plumage, bare part color has the potential to be highly flexible. For example, carotenoid-based bare parts can lose their color within days of food deprivation or within hours of stress. Amidst growing suggestions that changes in bare part color could have important implications for signaling, one of the authors, Jordan Karubian, was studying Red-Backed Fairywrens (Malurus melanocephalus) in Australia. In this species, males either acquire a territory and display black breeding plumage and bills, or stay dull and serve as helpers at the nest. Jordan noticed that when a breeding male died and a dull male took over its vacancy, the dull male’s bill would darken within several weeks. Experiments confirmed this effect and showed that dull males with newly black bills also had testosterone levels comparable to birds with black plumage. I joined Jordan’s lab as an undergraduate and studied fairywrens as well, and when I was looking for a topic for an honors thesis Jordan suggested that bare parts were an expanding area in need of a review. That thesis grew and grew, eventually becoming my master’s work and encompassing 321 published studies of bare-part coloration and signaling.

Our review shows that despite the research focus on plumage, bare part signals might be more common than plumage-based ones and are an important visual signal in many species that lack bright plumage altogether. Carotenoids, melanin, and structural colors are all flexible in bare parts, and rapid blood flushing through skin can change color even more rapidly. Bare part color provides up-to-date information about a signaler, allowing competitors, mates, and offspring to adjust their strategies and maximize their fitness. Carotenoid-signaling with bare parts may also be less costly than with plumage, allowing signaling by females and non-breeding males. In species where both plumage and bare parts of the same color exist, the two are likely to be ‘multiple messages,’ conveying different aspects of condition or targeting different audiences. We believe that more careful and extensive characterization of bare part coloration will contribute greatly to our understanding of this underappreciated dynamic signal, and help inform a more inclusive theory of animal communication.

Song Diversity Hints at Thrushes’ Evolutionary Past

AUK-16-222 Figure 1

A spectrogram of a Hermit Thrush song shows the introductory note (at left) and the more complex song that follows.

The Hermit Thrush is famous for its melodiously undulating song, but we know very little about whether—and if so, how—its songs vary across the large swath of North America that it calls home in the summer. A new study from The Auk: Ornithological Advances provides the first thorough overview of geographic variation in Hermit Thrush song structure and hints at how isolation and adaptation shape differences in the tunes of a learned song within a species.

Sean Roach and Leslie Phillmore of Nova Scotia’s Dalhousie University gathered recordings of Hermit Thrush songs from a number of databases, accumulating a sample of 100 individuals recorded across North America between 1951 and 2015. Spectrographic analysis revealed significant differences in song structure across the three major populations—Northern, Western Mountain, and Western Lowland—as well as within them. The most striking differences were in the pitch of the introductory notes that preface the birds’ songs, with Western Lowland thrushes producing higher, more variable introductory notes than their relatives elsewhere.

“Though Hermit Thrushes have a beautiful, well-known song, relatively little is known about their singing behavior,” says Roach. “Knowing how the species varies with respect to genetics and morphology, I became interested in how their song varies, as song can play an important role in processes like speciation.” Some of the variation the researchers found likely dates back to isolation of different Hermit Thrushes populations by ice sheets during the Pleistocene era, while differences between the two western groups may relate to body size, with larger birds producing lower-frequency songs. One group of high-altitude birds in the Canadian Rockies sang songs that stood out other members of their subspecies, which Roach and Phillmore believe is an adaptation to how sound carries in their open, shrubby habitat.

“Genetic studies of Hermit Thrushes in North America have defined three different groups of subspecies, with major splits most likely occurring as a consequence of two glaciation events. Roach and Phillmore show convincingly that these three major groups of Hermit Thrushes can also be defined by the introductory whistle note of their songs,” according to Williams College’s Heather Williams, an expert on song diversity who was not involved in the study. “The whistle note’s relative consistency across large geographical distances may be due to its role in long-distance communication of species or subspecies identity, while the remainder of the song could be under fewer constraints and its variability may carry more information about individual singers.”

Geographic variation in song structure in the Hermit Thrush (Catharus guttatus) is available at http://americanornithologypubs.org/doi/full/10.1642/AUK-16-222.1.

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.

Male Birds Adjust Courtship Behavior Based on Social Context

AUK-16-214 1 J Welklin

A male junco reacts to a caged female. Photo credit: J. Welklin

Male birds that have already paired up with a female aren’t above looking for a little action on the side. A new study from The Auk: Ornithological Advances explores how male juncos adjust their courtship behavior to their social landscape, finding that while both paired and unpaired males will try to get the attention of a new female on their turf, they go about it in different ways.

A male bird’s courtship behavior can be affected by factors like his size and hormone levels, but ornithologists are increasingly realizing that social context—whether or not the male already has a mate, and what other birds are around to witness his exploits—also plays a role. Dustin Reichard of Ohio Wesleyan University (formerly Indiana University) and his colleagues set out to tease apart the roles these different issues play in the courtship of Dark-eyed Juncos, comparing how unpaired males, paired males whose mates were present, and paired males whose mates were elsewhere behaved when presented with a new female.

They found that paired males approached females more rapidly, spent more time close to the females, were more active, and spent more time with their body feathers erect than unpaired males. Paired males also sang fewer long-range songs than their single counterparts, perhaps not wanting other birds to overhear, although the actual presence or absence of their mates didn’t affect their behavior.

Reichard had noticed variation in male juncos’ behavior during previous work to record their courtship songs, which led him to start developing hypotheses about what might underlie those differences. “Our results highlight the importance of considering both intrinsic and extrinsic factors when investigating the causes of variation in male courtship behavior,” says Reichard. “The focus of the field has generally been intrinsic factors, such as male condition or circulating hormone levels, but our results suggest a potential role for eavesdroppers and social context in addition to condition-dependent factors.”

Reichard and his colleagues conducted their experiments at Mountain Lake Biological Station in Virginia, placing caged female juncos in front of free-living males and observing the males’ reactions. After each trial, the researchers captured the male to record his size and weight and take a blood sample. “Often the male’s mate would respond aggressively to the caged female, diving at the cage while pausing occasionally to chase her mate away from the area. The males were usually shameless during this process and continued to approach while singing and displaying, but to our knowledge none of the pairs in our study divorced as a result of this brief infidelity,” says Reichard. “People called me a ‘junco homewrecker’ during these experiments, but there’s little evidence to support that accusation.”

In the future, Reichard hopes to explore the possibility that males use different strategies to target potential social mates—females they’ll raise chicks with—versus “extrapair” mates. According to Auburn University’s Geoffrey Hill, an expert on mate choice in birds who was not involved in the research, “This study shows the potential for extremely complex behavioral interactions in birds that were long thought to be bland monogamists.”

Condition- and context-dependent factors are related to courtship behavior of paired and unpaired males in a socially monogamous songbird is available at http://americanornithologypubs.org/doi/full/10.1642/AUK-16-214.1.

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: Common Murre Parenting 101: How to Negotiate for an Easier Job


Researcher Linda Takahashi observes nesting murres. Photo credit: N. Oberlander

Linda Takahashi

Linked paper: Turn-taking ceremonies in a colonial seabird: Does behavioral variation signal individual condition? by L.S. Takahashi, A.E. Storey, S.I Wilhelm, and C.J. Walsh, The Auk: Ornithological Advances 134:3, July 2017.

When mates share parenting duties, conflict can arise over which one performs the hardest jobs. Common Murres are monogamous long-lived seabirds that raise only one chick each year. Extensive contributions from both parents are obligatory for successful chick fledging: Chicks are rarely abandoned, and murres are great parents. Throughout the three week chick-rearing period, one parent remains at the nest site, brooding and defending the chick, while the other is most often away from the colony foraging.  Murres have the highest wing loading of any flying bird, and so foraging far away from the colony, which is often necessary in years of reduced capelin availability, is energetically costly. Remaining in the colony with the chick is simply the easier job.

All things being equal between the murre parents, we’d expect that they would take turns and share the harder job of chick provisioning. For the most part, this is indeed what they do. One mate returns to the colony with a fish, feeds the chick, and the takes over brooding duties while the former brooder leaves. We called this a regular nest relief. However, some nest reliefs are irregular, such as when the returner comes back without a fish or the brooder doesn’t give up the chick, causing the returner to leave again to forage. We wondered if variation in nest reliefs was related to the relative physiological condition of the partners and whether changes in specific behaviours that occur during the nest relief ceremony were indicators of the partners “negotiating” with each other for the easier parental job.

Until our study, little focus had been given to the often-subtle behaviours shown by murres during nest relief (turn-taking) ceremonies. We looked at 16 pairs of Common Murres breeding in Witless Bay, Newfoundland, Canada, in 2009, a year with particularly low availability of capelin, the preferred forage fish. Pairs were identified by colour bands and nest location on the cliff. From dawn to dusk, we sat in a tiny observation blind and recorded murre behaviors with either a camcorder or an event logger. Specifically, an interaction began when a returning bird arrived at the nest, typically with a fish, and joined its chick-brooding partner, and it ended when one of the pair departed. We noted whether the parents traded roles and recorded their patterns of allopreening and bill-fencing. We also examined the relationships between murre condition—specifically, body mass and lipid metabolite levels (as measured by beta-hydroxybuterate)—and behavioural variation during turn-taking.

We found that irregular turn-taking ceremonies took longer than regular ones and had either delayed or non-synchronous allopreening. When a returning partner came to the nest without a fish, it began allopreening sooner than both the brooding partner and birds that returned with a fish. These “no fish” irregular nest reliefs took the longest of all, and brooders appeared to resist or delay leaving the colony. In cases where there was no exchange of duties, i.e., the brooder remained in the colony, rates of allopreening by the brooder were significantly lower than they were in all other types of turn-taking ceremony. Birds with higher overall chick-feeding rates brought fish on more visits than other birds, suggesting that that they were higher-quality individuals. Furthermore, brooding birds in relatively better condition departed the colony sooner after their mate fed the chick compared to those in relatively worse condition. We suggest that variation in allopreening allows mates to communicate with each other regarding their own condition, and, if that condition is poor, to negotiate for the easier parental duty, i.e., brooding.

Why would murres benefit from responding to signals about their mates’ condition? Since murres typically retain their mates for several years, parental investment theory predicts that it is in an individual’s best interest to preserve their mate’s current and future body condition as well as their own. Deterioration of a mate’s condition could lead to nest abandonment or even compromised survival. This paper shows that variation in ceremonies is one way to make information available to mates. Thus, behavioural variation during the ceremony can signal individual condition and be a means to negotiate parental roles.