Every year, the American Ornithological Society presents a range of awards honoring members for their stellar contributions to science and their impactful service to the organization. The 2019 recipients will accept their awards at the annual AOS meeting in Anchorage, Alaska, this June. Their work spans the full breadth of avian science, including contributions to evolution, conservation, systematics, and genetics, as well to the profession of ornithology itself. Awardees represent the broad diversity of our members, who are making major contributions to ornithology and to the Society.
“Honoring the achievements of our colleagues is an annual highlight for AOS leadership,” says AOS president Kathy Martin. “Under the northern lights of Anchorage, AOS will recognize a stellar array of ornithologists who will receive these prestigious awards for 2019.”
Color bands, leg flags, and other field-readable marks are a core component of the ornithologist’s toolkit. Mark-resight studies have led to invaluable insights into the demographics, movements, territoriality, and migration patterns of birds. But clear, confident IDs can be hard to obtain in the field. Colors are difficult to distinguish in low light or when worn, alphanumeric codes are easily mis-remembered or mis-recorded, and was it blue on the left, red on the right, or the other way around? The potential for misidentification is high, and that could have serious consequences for analysis and inference.
Mark-recapture models allow us to estimate demographic rates, but they assume that tags are not lost or misidentified, which is not always the case. Consider a bird that is captured in 2005 and marked with a leg flag with code A4T. This bird is resighted each year and dies in 2010. Now fast forward to 2015, when another bird, this one with flag 4AT, is seen but mistakenly recorded as A4T. Not only do we miss 4AT, but we have also mistakenly increased the apparent survival rate of A4T, and this could become a big problem if misread rates are high. In our recent paper published in The Condor, “Effects of individual misidentification on estimates of survival in long-term mark-resight studies,” we try to work out how frequently this happens and its effect on our ability to accurately estimate survival rate.
Delaware Bay is a globally important spring stopover site for Arctic-breeding shorebirds, a group of high conservation concern. Over the last 13 years, the Delaware Shorebird Project [http://www.dnrec.delaware.gov/fw/Shorebirds/Pages/default.aspx] has marked Red Knots, Ruddy Turnstones, and Sanderlings passing through the area with individually identifiable leg flags. This work relies on volunteers who count, trap, and band birds and resight individuals each year. These volunteers have widely varying backgrounds and experience and spend differing lengths of time with the project, resulting in a lot of variation among observers’ level of training and experience with resighting birds.
The leg flags we use in Delaware Bay are commonly deployed on shorebirds around the world. For many years, my coauthor Dr. Nigel Clark has been concerned about the potential for misidentification and its consequences, but misread error rates are hard to quantify. So, in 2008 he randomly withheld 20% of the flags manufactured for that field season. This provided us with real possible codes that were never deployed and a way to directly estimate the minimum error rate in our dataset if erroneous resightings of those codes appeared in the data.
We also estimated a maximum possible error rate to get a sense of the range of possible error rates in our dataset. In Delaware Bay, individuals are often seen several times a year and by multiple different observers. Considering this, we identified records where a bird was only recorded once in a year as possible misreads, which we used to estimate maximum possible misread rate, since it seemed unlikely that the same misread error would occur more than once in a year.
Based on resighting data from 2009-2018, we estimated that the minimum misread error rate in our data was 0.31% and the maximum was 6.6%. We found that both average error rate and the variation among observers decreased with experience (the total number of flags an observer had resighted). Our study showed that failing to account for misreads can lead to an apparent negative trend in survival probability over time when none exists. In our paper, we also explore some ways to help mitigate the effects of misreads through data filtering.
Volunteer-based citizen science programs provide rich datasets that can help us understand the drivers of population dynamics and declines. However, when individual misidentification is possible, it’s important to understand error rates and filter potentially suspicious records to avoid biased inferences. Failing to do so could have serious implications not only for our understanding of population declines, but also for the conservation decisions we made based on those analyses.
Many species of woodpeckers depend on mature forest. Usually, it’s because they need large decaying or dead trees for foraging and excavating nest holes. Since they roost overnight in their old nest cavities, we usually don’t think about roost cavities as a separate consideration for conservation management.
The Helmeted Woodpecker (Celeus galeatus) is different. We know this globally vulnerable species is associated with well-preserved, native Atlantic Forest, but why? We radio-tracked Helmeted Woodpeckers in Argentina’s Misiones province to learn more about their foraging, nesting, and ranging ecology, as well as their coexistence with other woodpecker species. We expected their roosting behavior to follow the pattern of other woodpeckers, with roost sites predominantly in excavated cavities.
Not so. We found 21 roost cavities used by at least 15 individual Helmeted Woodpeckers. Incredibly, none of them were excavated. All of the roosts were in cavities formed by natural decay in large, usually living trees. This makes the Helmeted Woodpecker unique.
Helmeted Woodpeckers, it turns out, have a lot of unusual roosting habits. Although other woodpeckers descend into their cavity to roost, Helmeted Woodpeckers go up inside the cavity and cling to the wall above the entrance. After nesting, each parent takes a fledgling to its separate decay-formed roost cavity, where they roost together for up to 67 days. So they don’t just need decay-formed roost cavities, they need decay-formed roost cavities with sufficient interior space above the entrance for two individuals.
Helmeted Woodpeckers can excavate cavities – they do it for nesting. They often forage on small dead branches and bamboo stalks, which are common in disturbed forest patches. But these birds are found primarily in old forests, and the fact that they roost in decay-formed cavities, which occur mainly in large, old trees, may go a long way toward explaining this association.
The cavities that Helmeted Woodpeckers use as roosts are in high demand by other forest animals, too. We found eight other bird species and at least two species of social insects using these cavities. Helmeted Woodpeckers fought to defend their roost cavities and sometimes lost them to White-eyed Parakeets (Psittacara leucophthalmus) and White-throated Woodcreepers (Xiphocolaptes albicollis). We think these roost cavities are a high-quality, limited resource, critical not just for Helmeted Woodpeckers but for a broad suite of forest species.
Helmeted Woodpeckers have already lost over 90% of their former range to deforestation, and nearly all remaining forests in their range have a history of selective logging. Unfortunately, logging operations target the same species and sizes of trees that typically hold Helmeted Woodpeckers roost cavities. To stop the ongoing decline of Helmeted Woodpeckers, the largest living trees should be retained in logging concessions, and more forested areas should be spared permanently from timber production so that they can return to old-growth conditions.
So what did we learn about how House Finch songs have changed since the 1970s—the equivalent of a millennium of cultural evolution in human terms? Here are the main results, and how we interpret them. We have to be careful with interpretation, though, as we cannot be sure that the differences we observed represent consistent trends; it’s possible that the birds have been fluctuating through the years and we merely caught two random points.
All the main features of House Finch song in 2012 (such as song length, pitch, and syntax) are within the same range as they were in 1975.
Because the basic characteristics of House Finch song have remained consistent across the decades, birds today would probably still recognize old recordings as being from their own species. We’re soon going to test this to find out for sure!
Roughly half of the individual syllables that were around in 1975 were around in 2012, too. The more common the syllables were in 1975, the more likely they were to still be in use by 2012.
However, none of the particular songs (that is, sequences of syllables) that we recorded in 1975 were sung by any bird in 2012.
These results are to be expected. Since House Finch syllables are learned whole, they can be preserved from generation to generation; perhaps birds even reinvent the same syllables over time. However, young birds individually assemble syllables into songs each generation, and there are millions of combinatorial possibilities.
The population of songs is more diverse (there are more different syllables in use) in 2012 than there were in 1975.
Although birds shared songs with each other in 1975, the birds in our 2012 sample didn’t share any songs with each other, despite being the same distances from their neighbors.
We know that the population of House Finches generally grew and expanded between 1975 and 2012, although a nasty outbreak of conjunctivitis was decimating the population for a while. A larger population means more neighbors to listen to and more individuals to create new syllable modifications as they learn. Both of these factors should eventually cause greater overall song variety, which is what both of these results show.
As is typical in science, we also found results we cannot readily explain:
Birds in 2012 do not repeat their songs as reliably as they did in 1975—they are more likely to skip syllables, add new ones, or switch them around.
Individual songs in 2012 have fewer different kinds of syllables than they did in 1975 (despite there being more total syllable types in use in the population as a whole!).
In 2012, the syllables that are more common tend to be the ones that are more complex—they change pitch more rapidly and more often. They also tend to be higher pitched. This was not the case in 1975.
We’re developing some ideas to explain these curious results—hypotheses that will inspire our next round of field and laboratory work. The House Finch researchers in our lab are taking some exciting next steps, looking at such things as song similarity over geographic distance, changes on islands, early song development, social networks, and sex differences.
Unfortunately, Paul Mundinger passed away while this study was being conducted, and he never got to see the results. But it is because of his early work that we were able to chronicle changes in these songbirds over nearly four decades, and his song recordings (which are voluminous) will continue to provide us with interesting baseline data and prompt new research for years to come.
The first bird song I ever recorded was that of a House Finch. When I was a kid growing up in Leominster, Massachusetts, the bird that nested behind my front porch lamp would fly out to a particular birch tree or the telephone wire and belt out a complex four-second warble over and over again. That sound became emblematic of summertime for me and my siblings. One day when I was in my room holding my tape recorder against the radio speaker to record songs (human songs, that is!), I heard the little red fellow outside start doing his thing, and I promptly stuck my recorder out the window for an acoustic memento. I actually ran across this cassette tape for the first time in nearly four decades a couple of months ago, coincidentally just as my first scientific paper on House Finch song was about to be accepted for publication in The Auk.
Here are a couple of examples of House Finch song. Read it like sheet music, with time on the horizontal axis and pitch on the vertical—it’s composed of a bunch of notes, or syllables.
The reason my research collaborators and I are interested in House Finch songs today is because these songs change over time and space—we’d like to know how and why they change the way they do. Most animals simply inherit the noises they make, and so the sounds don’t change much from generation to generation. About half of the world’s birds, however, learn how to “speak” as juveniles from older members of their own species, just as we humans do.
The youngsters don’t always imitate perfectly the songs they learn, and so over the generations small changes in these songs can accumulate. These changes result in noticeable song differences across time and space, just as we humans diverge in our accents and languages. For this reason, bird song is an important animal model system for the study of cumulative change in socially learned traits, what’s known as “cultural evolution.”
Long-term changes in bird song are rarely studied, because research projects don’t often last for decades. However, even as I was listening to that House Finch from my bedroom, Dr. Paul Mundinger, a professor at Queens College at the City University of New York, was recording them on western Long Island, in high quality and accompanied by meticulous field notes. Paul had just published a paper in The Condor showing that House Finches can have different song dialects. He had also indicated that young House Finches learn their songs by listening to a bunch of singing neighbors and assembling chunks of syllables from several of them, like an acoustic collage. The end result is two to four songs that an individual will sing consistently for the rest of its life.
Fast forward 37 years, and I, a new professor at the same college, became Paul’s friend and colleague. He was pleased to hear that I wished to pick up where he had left off with House Finch song in the 1970s (after which he had moved on to research on the canary). I was excited to compare his early House Finch recordings to the songs sung by local birds today. Because birds’ generations are so much shorter than those of humans, this would be like comparing our English to that used a millennium ago in the epic story Beowulf, which is so different from our modern language that it would be unintelligible to most English speakers today.
The main two steps in this study would be (1) to see what songs these Long Island House Finches are singing today, and (2) to find a reliable way to compare songs across time. Two doctoral students in my lab stepped up to the task. Franny Geller loves observing and recording birds, and so she recorded as many House Finches as she could find in western Long Island in 2012, and Chenghui Ju is a computational wiz who programmed software specifically to characterize and compare House Finch songs in different times and places. This study became part of Chenghui’s recent doctoral dissertation.