Birds have some awesomely descriptive names. Like the Yellow-bellied Sapsucker (Sphyrapicus varius), a North American woodpecker that specializes in drilling “sap wells” in trees to feed on their sugary phloem sap. Or the Brown Trembler (Cinclocerthia ruficauda), a Caribbean relative of the mockingbird that shakes its wings violently to communicate with other members of its species. But when it comes to quirky but descriptive names, the African oxpeckers are hard to beat.

A Yellow-billed Oxpecker (Buphagus africanus) foraging on the back of a large mammal. Photo by Steve Garvie.

You may not realize it, but you’ve probably seen oxpeckers in nature documentaries: small brown birds with festive red-and-yellow bills, traveling about the African savannah perched on the backs of large grazing mammals. As their name suggests, oxpeckers peck the animals on which they perch, harvesting ticks and other ectoparasites from the skin of their hoofed hosts. Their relationship is a classic example of a mutualism: an interaction in which each species benefits from the presence of the other. The hosts get rid of pesky ticks, while the oxpeckers get a protein-rich meal.

But the oxpeckers’ Latin name, Buphagus (literally “cow eater”), suggests a more sinister motive. Yes, oxpeckers eat ticks, but they have also been observed feeding directly on the blood of their hosts, opening new wounds or re-opening old ones. This behavior suggests that the relationship may be more asymmetric in its benefits: the birds might, in fact, be parasites.

Imagine being the biologist who first noticed this blood-feeding behavior. It would be like watching the guy washing windows on the apartment building next door as he suddenly stopped cleaning, looked around furtively, and took a bite out of the wall.

But is there any way to test whether the oxpeckers-ungulate relationship is fundamentally mutualistic or parasitic? In a paper published in Evolution last month, and colleagues took a comparative approach to answering this question. They began with two alternative hypotheses, both consistent with existing observations:

Hypothesis 1: The relationship is essentially mutualistic – ticks are the primary food source – but the birds sometimes feed directly on blood if it is accessible
Hypothesis 2: The relationship is essentially parasitic – blood is the primary food source – but the birds also feed on ticks when they are readily available

Another possible mutualism. Unfortunately, pirates are not indexed in the Global Mammal Parasite Database.

If the relationship is a mutualism, the authors predicted, oxpeckers should prefer host species that tend to harbor more ticks; more ticks means more food for the birds. If the relationship is a parasitic one, however, the birds should prefer host species that have thinner hides, which would allow easier access to the host’s blood.

Luckily, most of the “grunt work” of counting ticks on African mammals had already been done; the authors simply consulted the Global Mammal Parasite Database (yes, there is such a thing) to gather data on tick abundance on each host species. They also searched the literature to determine oxpeckers’ host species preferences and the hide thickness of each potential host.

Next, they needed to test whether oxpecker preferences were related to tick abundance or host hide thickness. As it turns out, this step is not as simple as it might seem. To understand why, try this thought experiment: Suppose that oxpeckers preferred several species of antelope over other possible hosts. These preferred antelope hosts had thinner hides than many other possible hosts (zebra, water buffalo, rhinoceros, etc.). Would these data be evidence enough that oxpeckers prefer host species with thin hides?

No, they wouldn’t, because although the antelope hosts all have thin hides, they also share lots of other characteristics due to their common evolutionary history – i.e., simply because they’re all antelope. So you couldn’t be sure if it was the thin hides that attracted the oxpeckers to these species, or some other trait shared within the group. To account for this possibility, the authors needed to construct a phylogeny – an evolutionary family tree – that included all of the oxpecker’s possible host species. Nunn and colleagues obtained DNA sequences from GenBank (an online DNA sequence data repository) and used these data to reconstruct the evolutionary history of the African mammals in question.

With this phylogeny, the authors were able to use a statistical model that infers ancestral characteristics based on the branching pattern – or topology – of the tree, then asks whether evolutionary changes in one variable (e.g. hide thickness) are accompanied by changes in another (e.g. oxpecker preferences).

An aside: Remarkably, all the data required for this study were already available in other published sources. I used to work for Walter Koenig, one of the authors of this study (not this one)… In addition to his empirical research, which includes some really seminal work on the social behavior Acorn Woodpeckers, Walt has a special talent for breathing new life into old data. This paper is a great example of the latter!

So, what’s the upshot? The authors found a positive relationship between tick abundance and oxpecker preference: on average, the more ticks were found on each host species, the more oxpeckers liked that species. Oxpeckers also preferred larger hosts – which tended to harbor more ticks – but even among host species of similar size, oxpeckers preferred the species with the most ticks. On the other hand, oxpeckers didn’t seem to care much about the thickness of the host’s hide.

These patterns were identical between the two species of oxpecker, the Yellow-billed Oxpecker (Buphagus africanus) and Red-billed Oxpecker (B. erythrorhynchus). Taken together, these results favor the mutualism hypothesis over the parasitism hypothesis.

One way or another, oxpeckers are bloodthirsty. But this analysis shows that they tend to look for blood in convenient snack-sized packets – helping their hosts rid themselves of parasites – rather than collecting the blood for themselves. Personally, as much as I like a good paradigm shift, I find it reassuring to see a textbook “just so” story borne out with actual data. That said, it might not take much to change the nature of the relationship; if a host has readily accessible wounds, or if ticks are scarce (as in a captive situation) the birds can easily switch their tactics!

Nunn, C., Ezenwa, V., Arnold, C., & Koenig, W. (2011). MUTUALISM OR PARASITISM? USING A PHYLOGENETIC APPROACH TO CHARACTERIZE THE OXPECKER-UNGULATE RELATIONSHIP Evolution DOI: 10.1111/j.1558-5646.2010.01212.x

The conference is over and I’m en route to LA again. Turns out that I’m on the same plane as the guy who played Mini Me in the Austin Powers movies, and yeah, he’s pretty darn small in person. Anyway, the last two days of the conference were even better than the first two. On Saturday and Sunday, the true meaning of the “unconference” style became clear — in most sessions, leaders introduced themselves and simply posed some questions to start a discussion, then acted as facilitators more than presenters. It was a really egalitarian way of doing things, almost unnecessarily fair given how much more experienced many of the leaders were than the other participants. But, unwarranted fairness aside, some excellent discussions resulted!

On Saturday, I went to a session on using blogs as a tool to develop your writing (and, potentially, to begin writing a book), which was led by many of the authors from Friday’s “Books and Beer” happy hour. My favorite idea from this session was that a blog can be a sort of “writing laboratory” for trying new content, styles, formats, etc. Then, in another session, we had a great discussion about technology and the wilderness — e.g., how much technology is appropriate to introduce into the “wilderness” experience? Can technology enhance our connection with nature rather than diminish it? Some good arguments and examples were given on both sides. Then, Joanne Manaster and “science comedian” Brian Malow led a session on communicating science using humor. I think this was one of the best sessions of the weekend; humor is so seldom used in science communication, and a sense of humor is an attribute that I think the public often believes that we scientists lack.

Later in the day, Melody Dye and Allie Wilkinson led a cool session on using photography to communicate about science and the environment. Obviously, I had some ideas to contribute to this one People were very keen to learn how to create better pictures of their work and how to collaborate with photographers who already have the skills to do so. Then, a very well-structured session on how to write science blog posts, from choosing content to writing style, to marketing your posts, etc. And finally, and Joanne Manaster ran the first ScienceOnline film festival, with 10 entries (including my final “video blog” assignment from Jeff Morales and Colin Bates’s Science Filmmaking workshop in October).

Saturday’s banquet was a lot of fun, with an inspiring keynote presentation by Meg Lowman, a rainforest canopy biologist and champion for public outreach in science. Meg (aka. “Canopy Meg”) is currently serving as the Director of the new Nature Research Center at the North Carolina Museum of Natural Sciences (opening in early 2012) and a professor at NC State University. Brian Malow followed with a great performance that had us in stitches. really killed I was honored that the “video blog” that I created with Kelvin Gorospe and Annie Schmidt in Bodega Bay was voted the runner-up in the film festival! I got an inflatable Brotosaurus, which honestly looked a lot more like Brachiosaurus than anything else. The winning video really deserved it: a funny, fascinating short about how a photocopier works (see it ). And the 2nd runner-up was the great “” by alpinekat.

Sunday’s sessions were good, too… although most of the conference-goers seemed a bit groggier than they had before the previous night’s festivities. There was a very interesting session on alternative careers in science (i.e., those off the tenure track). One of the upshots: You still need a Ph.D., even for the so-called “alternative,” non-academic careers in science. In a session about engaging undergraduates in science communication, we heard about some interesting models for getting students involved Then, in the last session before lunch, we heard a very interesting discussion of e-books and how they’re likely to change the way we present science in books (in a good way, I think!). We saw some really cool examples of e-books and “app books” that integrated prose, animations, and active links to additional web media. Finally, after lunch I attended a discussion on marketing yourself in science, and how to create and maintain your “brand.” This is something I know I need to do better, especially given my only partially-overlapping photography, video, and science endeavors!

For what it’s worth: there were FIVE sessions in five different meeting rooms going at any one time, so what I described above is a mere 20% of the total content of the meeting! There really was a tremendous amount of quality discussion happening, on a huge range of topics. If you’re following this blog because you’re interested in communicating science (especially on the web), I highly recommend attending a future meeting!

Wow, I’ve already met a ton of interesting folks here, doing a lot of great stuff, and the meeting technically begins this morning (Saturday, January 15). I began the day yesterday by finishing and submitting a fellowship application from my hotel room (whee!), and then — entirely separate from the conference — I met up with Rob Nelson of Untamed Science, a production company that I blogged about last fall. Turns out, Rob is a great dude and we had some fun conversations about science, filmmaking, and the stuff that his crew is currently working on.

Then I got to have lunch with NESCent’s Robin Smith, Craig McClain, and Jory Weintraub, as well as fellow NESCent evolution blog contest winner Danielle Lee (you can read her winning post and the rest of her cool blog ). In the afternoon, the startlingly energetic (I’m just jealous ) co-led a workshop with Joanne Manaster on producing high-quality science videos. It was a great introduction to the medium, for a crowd mostly comprising science bloggers. I was intrigued to hear that on blogs that have both video and text content, video-based posts and text-based posts attract almost completely non-overlapping audiences… Later in the afternoon, Clifton Wiens of National Geographic Television gave a candid presentation on pitching science programs for television. The take-home message? It’s hard! Connecting with an audience requires a great story, and just because something’s exciting to fellow scientists doesn’t mean it will sell.

Finally, happy hour and dinner with the the authors of 30-odd books penned by conference attendees. I’m exhausted already, and things are just getting started!

I arrived in North Carolina’s Research Triangle Park yesterday afternoon, just in time for the opening keynote address at the ScienceOnline2011 conference. Robert Krulwich gave a wonderful presentation on how he and Jad Abumrad make science accessible to everyone – really, EVERYONE – on their NPR program Radiolab. If you aren’t familiar with the program already, you really owe it to yourself to check it out.

I finally met Carin Bondar (who will be leading a session on producing science videos today!), and I also had a fascinating discussion with a guy who has patented a skin treatment (“Nitrocell”) that ostensibly replenishes your body’s natural biofilm of ammonia-oxidizing bacteria, helping your body maintain proper levels of nitrous oxide (NO). This biofilm, he claimed, gets washed away when you bathe. Anyway, this fellow claimed not to have taken a shower or bath in… wait for it… over 8 years. But because he had a healthy biofilm goin’ on, all was well I’ll give this to him: he didn’t smell like a guy who hasn’t washed himself in nearly a decade. So maybe there is something to these ammonia oxidizing bacteria? Anyway, his biofilm-restoring treatment is for those of us not adventurous enough to embark on a multi-year non-bathing experiment.