A Return to Discovery
(Originally published February 1st, 2015 on http://scienceofbirds.blogspot.com)
Well folks, it’s about time I got back to blogging.
The river of discovery beckons…Though my hiatuses (hiati?) from blogging are never deliberate, they happen sometimes. Since you last read about ornithology here, I returned to my internship at the Field Museum’s Bird Division and later to my staff position at Makajawan Scout Reservation. Perhaps the highlight of the summer, though, was experiencing the full splendor that is The Cornell Lab of Ornithology through the Cornell Young Birders’ Event. The people and Lab both are inspiring, to say the least. They have an incomparable ability to feed the natural history fire in your belly; I hope to bring some of that back to you.
Since this past summer, a season that was oh so short, I’ve continued to make music with my tuba, explore the “wilds” of Illinois and its avifauna, and work on some projects — projects like PhenCal, an inspiration-based magazine called Manifest, and maintaining my social media outreach.
But though this blog has grown quiet, the world of ornithological research has been anything but. New research has been breaking into the scene daily, some of it so exciting that I may just have to share it with you now, synopsis-style.
There is so much being learned out there right now, but it’s nice to have start with some of the most interesting bits. With an awareness of that ornithological curiosity, here’s some of the fruits of my gleaning through the research, Foliage-gleaner style.
Feel free to read any or none of the following, but if you do, I encourage you to read it in pieces. It’s an ambitious post, sort of like three-in-one, but hey, I’m making up for lost time.
Pectoral Sandpipers are among the most accomplished non-passerine songsters — researchers look into how
When one ponders why they’re interested in birds, song is one of the highlights of experiencing the avian world. From familiar voices like the ethereal warbles of the Hermit Thrush, the nostalgic whistles of a White-throated Sparrow, or the bold notes of the Northern Cardinal, to exotic voices like the incomparable, sizzling gurgle of the King-of-Saxony Bird-of-Paradise, the machine-gun trill of the Brown Sicklebill, or ear-piercingly loud White Bellbird, song is one of the most distinctive facets of Aves. One little detail, however, stands out after a little extra exploration. When people talk about birdsong, most if not all of the go-to examples are songbirds (Passeriformes, or passerines for short). All the examples above, hailing from such diverse families as the Thrushes to New World Sparrows to Birds-of-Paradise to Cotingas, are passerines. Surely song can’t be limited to the birds that bear its name!
As I’m sure you’ve guessed, it’s not.
many pieces that make a complete Pectoral Sandpiper
display. See first citation.
Song is a mate-attraction strategy. Whichever sex of a given species competes for mates of the opposite sex (most of the time it’s males) is subject to sexual selection, where traits that are more attractive to potential mates are passed on, whereas less attractive traits aren’t. Sexual selection is responsible for peacock tails, cardinal reds, and every complex song out there. In some species, like birds of prey, potential mates don’t find self-broadcasting behaviors like song attractive. But in others — especially species that have limited time and resources to breed — self-broadcasting is an extremely useful way for the competing sex to communicate their quality and the quality of their resources through the complexity of their songs. It is, to say it with brevity, efficient. Species that require this efficiency will have sexual selection acting on behaviors like song.
Not surprisingly, then, do we find that many arctic-nesting shorebirds have elaborate songs and song displays, and one of the foremost among them is the Pectoral Sandpiper (Calidris melanotos). To quote Andrew Spencer of Earbirding,
“The classic “song” of the species is unlike any other sound on the Arctic, and any other shorebird in the New World — the male bird sits on an exposed tussock, slowly inflating its pectoral pouch and ruffling its black-based breast feathers before suddenly launching itself into the air and flying low over the ground. Partway into the flight its wings slow into a more exaggerated butterfly flight and it begins emitting a low-pitched hooting series, pumping its head in time with each hoot while its expanded pectoral pouch hangs underneath like a bosom. Right after the series ends it suddenly undulates up into the air a few times before circling back around and landing again. It’s a show like no other!”
Having received more and more attention, researchers from the U.S. and Germany banded together to look into how they do it, and they found some fascinating stuff. I’ll report on just a few of them here. First, “Pecs” have evolved a vocal organ (syrinx) similar in anatomy to that of songbirds, a fascinating fact given that Pecs must have evolved this vocal complexity completely on its own. In evolution, this is called convergence. Also fascinating, Pecs show an ability to expand their esophagus similar to that found in doves and pigeons. Why? Males fill their throats with around 30 mL of air in preparation for their courtship display, though their throats have a capacity of up to 50 mL. All this just to impress females. Finally, Pectoral Sandpipers’ courtship displays are incredibly ritualized: their display includes three phases, each with different vocalizations and locations (ground or in flight). Different vocalizations are directed at different individuals as well, with some meant for competing males and some for females,
Needless to say, if you bird along Pecs’ migratory pathways, we would hardly recognize the same bird on their breeding grounds.
Bird Nest Design — More Complex and Fascinating than you Ever Would Have Suspected
Nest design in birds is fascinating, and not just because it’s, well, er, fascinating, but also because studying it forces us to rethink what we’ve assumed to be true. Science is, in spite of what we’d like to think, rife with assumptions. Luckily, most of these assumptions are small, insignificant, and don’t influence many decisions. But, alas, they are there, and they’re often cryptic. Clearing out that ambiguity can be a challenge, but when done as part of the quest to find truth rather than to be proved right, the results can be breathtakingly interesting.
Such is the case in a recent “review” paper called The design and function of birds’ nests. In this paper, the authors have systematically sleuthed through their own and a great variety of other authors’ research to produce a succinct, and elegant, set of overarching themes. Quick digression. Why do I love these kinds of papers so much? If one is researching a topic, typically he/she would have to hop between a great number of potentially unconnected papers, hoping to draw the right conclusions between them all. In review papers, fulltime, professional scientists have done that for you, and they’ve done it with access to more research, more great minds, and more cutting edge ideas. In short, they’re laying out all the research — and with it the prevailing ideas — on a particular subject for your convenience. It’s good stuff.
Anyway, back to the research. In birds, there’s a significant behavior that we — lay people and ornithologists — take for granted all too often: the nest. In ornithology, the prevailing assumption has been that nests are purely used by birds for nesting and nothing more. More specifically, the assumption is that nest design — and time spent building — is determined purely by natural selection, with the selective pressure, of course, being predation risk.
But there are lots of strange behaviors, found both in observational and experimental studies, that challenge seemingly obvious assumption. The best part? There are a lot of questions left to be answered. Let’s dive into some of the interesting bits (read as much or as little as you please):
- Nest site selection is highly influenced by predation risk. Interestingly, birds who nest high in the forest strata are at greater risk of predation from avian predators, but much lower risk from mammalian predators. Conversely, birds that nest low in forest strata are at high risk from mammalian predators and low risk from avian predators. Birds nesting halfway up are at equal risk from both. So (#FieldSkills), if you’re in an area where most of the bird species nest high, for example, it can be reasonably assumed that mammalian predation is more prevalent than avian predation. There are some other interesting observations from studies on nest placement in relation to predation risk:
- Some birds nest near wasp nests or other aggressive species like kestrels to reduce risk of predation, even if it puts them in a certain amount of dangerSome birds will actively shift their nest site halfway through the breeding season if the previous site proved to be rather predator-laden. This is interesting because it indicates that nest site selection is not purely genetic/instinctive, but rather that it is a combination of instinct and learning.Some birds will even track the amounts of rodents in their area and colonize more heavily in areas with heavy rodent concentrations. They do this because species that would prey on them prefer rodents, and with heavy rodent population, the predation risk is lower.
- Ground nesting birds instinctively “know” the color of their eggs and actively seek potential laying areas where their eggs will blend in
- Nests can be used to express the fitness of a potential mate…in other words, nest design is also subject to sexual selection (BIG IDEA)
- Sexual selection favors larger nests, able to house more eggs. This is in direct contrast to natural selection for small nests.
- Birds with high body condition invest more in nest building, indicating that the quality of a male’s nest can be used by the female to gauge the quality of the male as a mate.
- Male starlings integrate green plant material into their nests, and females respond by integrating feathers into the same nest. This is fascinating because it indicates that females are “impressed” by male presentation of green plant material, and are actively responding by investing more in the nest.
- Birds change their nesting habits with altitude as well. Nesting high in trees, and thus closer to the sun and its head, is common in high-altitude species. These nests average more insulated as well to account for more radical changes in temperature.
These points are only the tip of an iceberg of interesting information in this paper (which, by the way, is open access…click the image to the right!). The most important overarching theme is this: nest design is subject to natural selection AND sexual selection. An inconspicuous nest can hide chicks from predators, but it may also leave females unimpressed. Birds designing nests have a lot to take into account to protect offspring: microclimate, color of the environment, parasites, what nest insulation is necessary, how impressive a nest may be to the opposite sex, etc. And all this is reflective of the health (quality) of the nest site selector and builder.
I don’t know about you, but this stuff gets me excited. There are so many little details, so much nuance, that remind us of the staggering complexity of the world around us. What a privilege it is that we can even begin to figure it out.
I encourage you all to read the paper yourselves, and, as with any perpetual learner, to ask as many questions as possible. This paper does a good job of highlighting what’s yet to be learned; seize that opportunity!
A Flock of Genomes, plus Understanding One of The New World’s Largest Groups of Birds
This section is going to kill two birds with one stone, as the content of these two studies are similar.
In genetics, we’re in what may be called a golden age. Our ability to process huge amounts of genetic information in a short amount of time — also important: for a lower price — is growing beyond what people like Ernst Mayr and John Zimmer could have dreamed. This enormous volume of information allows us to draw better conclusions, answering questions fine and grandiose in scope. Check out this video to understand where genetics is at.
The complete history of birds is just such a grandiose question. Scientists from around the world, with focuses as varied as the countries they hail from, recently published a collaboration around this question at a scale perhaps never seen before. The project, called The Avian Phylogenomics Project, sequenced the ENTIRE GENOMES of 48 species of birds, each representing a unique place in the bird family tree. Its aim was to understand the bird tree of life, but it didn’t stop there. The project also answered questions about vocal learning, the genetic basis and history of birdsong, the loss of teeth, the molecular basis of flight, and endangered species. As I said, the scale of this project is breathtaking, answering questions previously unanswerable, and revealing links between birds, other reptiles, and even humans in the process.
The project released the bulk of its results simultaneously, producing a tsunami of head-turning curiosity throughout the scientific community and beyond. That’s 28 papers nearly at once, 8 of which were specially published by the journal Science (many of these are open access!).
Wow. There’s a lot to explore here, and I encourage you to do so. Really the most amazing part of this process is the level at which it allows us to ask new questions. Projects like these foster the future-ward momentum of science, and we can only dream like starry-eyed kids about where it will go next.
In a similar vein, a paper was published only a few days ago about one of the more ambiguous branches on the bird tree of life. It’s a New World branch called the New World Nine-Primaried oscines, or the Emberizoidea. It includes well-known families of birds like Blackbirds and Orioles (Icteridae), Cardinals and Grosbeaks (Cardinalidae), Wood-warblers (Parulidae), New World Sparrows (Passerellidae), and Tanagers (Thraupidae). In all, the branch includes ~832 species, or 7.8% of all birds. These families have mysteriously evaded understanding by scientists since they were first described. Why? These 832 species are extremely varied, but not always in easily categorized ways. A great number of species and genera appear ostensibly similar when in fact they’re distantly related. Convergent evolution, in this way, muddles our understanding of this group. Emberizoid classification history is rife with lumps, splits, and reorganizations, and there are still many outstanding questions. We wonder about questions like where their diversity originated (North or South America), when it happened, what caused it, and why they’re so diverse now.
Well finally, these questions have been given a comprehensive set of answers. As demanded by the size of the group, the paper includes the largest near-species-level phylogeny ever constructed. What does this mean? The authors constructed a tree of life for the Emberizoidea with detail down to >95% of its ~832 species. This allows us to trace the evolutionary history of almost every one of those species back to the common ancestor of the entire group.
Like with the flock of genomes, this phylogeny answers more questions than just when and where species diverge. It also tells us that the ancestor(s) of the group crossed Beringia (an area now occupied by the Bering Sea where North America and Asia were once connected) into North America around 20 million years ago. This means the whole group originated in North America and then expanded southward, diversifying along the way. What governed much of this southward movement? Little more than the Isthmus of Panama. This Isthmus has a huge effect on New World biodiversity; varying sea levels through time determine whether or not it’s above sea level. When it’s above, North American flora and fauna can pass southward; when it’s not, North and South America are isolated.
The on and off connection of North and South America is a biological recipe for diversity, and the 832 species of the Emberizoidea today is evidence of this. But there’s a lot more to it….in order to understand it, I encourage you to read the paper yourself.
When you do, remember the significance of what you’re reading. Information like that in this paper has never existed before, and it will likely set the trend for how we understand the tree of life in the coming century.
The results of both of these papers have me in awe. Never before have we been able to understand the origin of species like we can today. I feel incredibly lucky to be alive when I am, to be a fly on the wall for research as grand and as discerning as this.
Overall, look at the breadth of discovery here (and this is a tiny fraction of the ornithological research that’s been published in the past 365 days)! In our time, we’re coming to understand the origin of species (not to mention genera, families, orders, and classes) in a way never possible before, finding new and fascinating behaviors hidden by long-held assumptions, and learning about the unique ways that birds tick. And this is just birds! Just ornithology! Imagine all there is to discover in other fields!
Surely, this post is evidence of one thing above all else: we do not know everything. Often, in these days of the internet, I come across a certain pessimism that there’s nothing left to learn. Certainly this is not true. Though Google can answer almost any question, if you dig deep enough, you can find questions of almost any scale waiting to be answered.
In this New Year, let’s go digging together.
Cheers, everyone. Thanks for reading.
CITATIONS:
Tobias Riede, Wolfgang Forstmeier, Bart Kempenaers, and Franz Goller (2015) The functional morphology of male courtship displays in the Pectoral Sandpiper (Calidris melanotos). The Auk: January 2015, Vol. 132, No. 1, pp. 65–77. doi: http://dx.doi.org/10.1642/AUK-14-25.1
Guojie Zhang, Cai Li, Qiye Li, Bo Li, Denis M. Larkin, Chul Lee, Jay F. Storz, Agostinho Antunes, Matthew J. Greenwold, Robert W. Meredith, Anders Ödeen, Jie Cui, Qi Zhou, Luohao Xu, Hailin Pan, Zongji Wang, Lijun Jin, Pei Zhang, Haofu Hu, Wei Yang, Jiang Hu, Jin Xiao, Zhikai Yang, Yang Liu, Qiaolin Xie, Hao Yu, Jinmin Lian, Ping Wen, Fang Zhang, Hui Li, Yongli Zeng, Zijun Xiong, Shiping Liu, Long Zhou, Zhiyong Huang, Na An, Jie Wang, Qiumei Zheng, Yingqi Xiong, Guangbiao Wang, Bo Wang, Jingjing Wang, Yu Fan, Rute R. da Fonseca, Alonzo Alfaro-Núñez, Mikkel Schubert, Ludovic Orlando, Tobias Mourier, Jason T. Howard, Ganeshkumar Ganapathy, Andreas Pfenning, Osceola Whitney, Miriam V. Rivas, Erina Hara, Julia Smith, Marta Farré, Jitendra Narayan, Gancho Slavov, Michael N Romanov, Rui Borges, João Paulo Machado, Imran Khan, Mark S. Springer, John Gatesy, Federico G. Hoffmann, Juan C. Opazo, Olle Håstad, Roger H. Sawyer, Heebal Kim, Kyu-Won Kim, Hyeon Jeong Kim, Seoae Cho, Ning Li, Yinhua Huang, Michael W. Bruford, Xiangjiang Zhan, Andrew Dixon, Mads F. Bertelsen, Elizabeth Derryberry, Wesley Warren, Richard K Wilson, Shengbin Li, David A. Ray, Richard E. Green, Stephen J. O’Brien, Darren Griffin, Warren E. Johnson, David Haussler, Oliver A. Ryder, Eske Willerslev, Gary R. Graves, Per Alström, Jon Fjeldså, David P. Mindell, Scott V. Edwards, Edward L. Braun, Carsten Rahbek, David W. Burt, Peter Houde, Yong Zhang, Huanming Yang, Jian Wang, Avian Genome Consortium, Erich D. Jarvis, M. Thomas P. Gilbert, and Jun Wang Comparative genomics reveals insights into avian genome evolution and adaptation. Science: 12 December 2014: 346 (6215), 1311–1320. [DOI:10.1126/science.1251385]
F. Keith Barker, Kevin J. Burns, John Klicka, Scott M. Lanyon, and Irby J. Lovette (2015) New insights into New World biogeography: An integrated view from the phylogeny of blackbirds, cardinals, sparrows, tanagers, warblers, and allies. The Auk: April 2015, Vol. 132, No. 2, pp. 333–348.
