The Bird's Nose Knows
by Julie Hagelin, Assistant Professor of Biology at Swarthmore, (Pa.) College
Julie Hagelin, who is on leave for the current academic year, discusses in the story below her ongoing research into the sense of smell among birds. Following the story, there are links to video clips about the birds she is studying.
Birds are a lot like humans in that they use sight and sound more so than other senses. You can see it in a bird's colorful feathers or beautiful song, both of which help to attract mates or communicate with others. Yet, a key sensory system that has been overlooked in birds is smell. Not only that, but whether birds actually produce odors that have a social function is nearly unstudied. That is, do birds use scents that communicate information to other members of the same species?
There is good reason to think birds may detect and produce social odors. Every other group of vertebrates - humans, fish, reptiles, and amphibians - has a fully developed sense of smell. Bird noses are structurally quite similar to the general vertebrate plan, and many ornithologists have noted that different bird groups emit surprisingly strong scents. In other vertebrates, odors function in numerous social situations that involve an exchange of information between members of the same species. This can be as straightforward as a dog marking its territory, or perhaps more complex, such as two animals displaying while they simultaneously assess the odor of a prospective mate.
So, why not birds?
The idea of chemical communication in birds is an entirely new way of viewing bird social behavior. It is a sensory channel that has the potential to alter how we traditionally interpret how and why birds behave the way they do.
Which brings me to the Kakapo - a five to seven-pound, flightless, nocturnal, vegetarian parrot. It's the largest, most critically endangered parrot in the world - just 86 remain. Kakapos only live in New Zealand, where they are regarded as a national treasure. The birds breed irregularly, every three to seven years, which can be a challenge for conservationists. They are also only active at night, so can be difficult to study.
Yet, it turns out, the Kakapo produces an amazing scent - like dust and honey - that is really striking, and very sweet. Furthermore, we recently discovered that the Kakapos' brain has one of the largest regions devoted to smell (termed the olfactory bulb) of any bird known. The bird's keen sense of smell was well-known to native Maori hunters of New Zealand, who always approached birds from down-wind while hunting.
I first saw a Kakapo when I visited New Zealand 15 years ago on a Thomas J. Watson Fellowship. I was interested in learning more about this unusual, endangered species. Back then, I was lucky enough to hold a bird while a ranger at a nature preserve put a small radio-tracking unit, or "backpack," on its back. Immediately thereafter, I noticed that my t-shirt smelled just like Kakapo (dusty and sweet), for the rest of the day!
That made me think further about odors and birds: What might scent signal? Could it function in breeding decisions, as in other animals? And, perhaps most importantly, could humans use odor information to help an endangered bird, like the Kakapo, breed more successfully?
The Kakapo is the Holy Grail of New Zealand conservation. Yet it is very difficult to work on an endangered national treasure when you only have a hunch! Instead, I first needed to verify that odors were, in fact, key to the social behaviors of other bird species. So, I decided to focus my research on a non-endangered species here in the U.S.
An amazing seabird called the Crested Auklet lives in the Bering Sea region of the Western Arctic. They are unusual in that they smell like freshly-peeled tangerines! In fact, you can generally smell groups of birds before you see them. We've found an unusual set of compounds that make up the auklet's citrusy scent - a mixture of simple alcohols and aldehydes - it is not what you find in tangerines, but it smells remarkably similar.
Each summer, students and I obtain permission from the local village of Savoonga, St. Lawrence Island, to conduct research on nearby colonies of the birds. We live in the local community of about 650 people for up to 10 weeks, where we are welcomed and exposed to interesting aspects of local culture. Many people on the island are fantastic artists who make beautiful carvings out of walrus ivory or hand-sew intricate articles of clothing from seal skin. Most children learn Yup'ik at home before they learn English in school. The kids and their parents are quite patient with us, as we try to learn the Yup'ik names of plants and animals that inhabit their backyard!
The island residents have known for ages that Crested Auklets produce a striking, citrus-like odor. However, students and I needed their help to learn, more precisely, when odor was produced. One resident of Savoonga prepared auklets for her family in March, a traditional hunting time, when auklets have just returned to local breeding sites. To our surprise, she told us that the birds she had plucked were completely unscented! Although these birds already exhibited all other ornaments used during breeding (long crests, orange beak plates), they completely lacked odor. This key observation made us realize that Crested Auklets produce odor sometime after they return to the breeding area. Scent is probably the last adornment that birds acquire before they seek a mate.
Crested Auklet odor is linked to a striking social display during courtship, in which two or more birds rub their faces in the scented nape of a display partner. Through work supported by the National Geographic Foundation, students and I ran experiments in the wild and in captivity to determine the function of auklet odor. This included making synthetic odor and putting it on rocks where auklets display within the colony to see how the birds responded to it. We also compared odor concentration of the plumage with a birds' social rank in a captive situation. Combined, we believe odor may be emphasized when males compete. That is, odor may relate to a male's social status.
Crested Auklets also nest underground in the dark [see video clip 2]. Students and I have wondered whether scent might act as a subterranean signal, where vision is obscured. We can view the secret nesting world of auklets via a small, infrared camera placed just inside the nest entrance. Below ground, we suspect odor could signal the return of a mate, or possibly alert a nest resident of an intruder, as birds often compete for prime breeding sites.
The study of sensory systems of any animal, including birds, is inherently multidisciplinary. There's something to study at every level, including chemistry, anatomy, reproductive physiology, and animal behavior. Consequently, it is always interesting and keeps students and me on our toes! I often am on the search to find assistants who are eager to help answer new questions with the aid of experts from a range of different disciplines.
Recently, we have begun a collaboration with Professor of Biology Amy Cheng Vollmer, an expert in microbiology. Students and I were suspicious that microbes on feather surfaces may contribute to the Crested Auklet's citrusy scent. We first collected auklet feathers in the field, then students in the Vollmer lab on campus revealed the microbes the feather samples contained. The work led to an honors thesis, which is now about to be published.
Since 2004, ten Swarthmore students have worked in the lab or in Alaska on projects related to auklet odor. Some have taken part in a cooperative relationship we have with the Aquarium of the Pacific in Long Beach, Calif., in which Swarthmore student interns design a summer project to conduct on a captive auklet population. Students interested in chemistry have worked at Monell Chemical Senses Center in Philadelphia analyzing the compounds and seasonal patterns of Crested Auklet feather odor. I encourage students to present posters at an annual, international chemical sensory conference. Everyone also participates in the on-campus Sigma Xi symposium. Our results are exciting, because they are a completely new way of interpreting bird behavior. I am currently helping several students organize their work for publication.
Scientists have been studying birds for hundreds of years. Yet, until recently, no one realized social odors occurred in birds. The more we learn about the tangerine scent of Crested Auklets, the more we are recognizing its potential use as the first-ever "olfactory ornament" to be documented in any bird. In Crested Auklets and a few other bird species, scent appears to be linked to key social behaviors, such as courtship and breeding, both of which are closely linked to reproductive success. Consequently, responses to bird odors may have practical application to conservation and management situations, such as those of the New Zealand Kakapo.
Biologists charged with Kakapo conservation in New Zealand are hopeful that my students and I are onto something. That is why, after many years, I have returned to New Zealand. We will be filming Kakapo activity at night in its natural habitat to test whether birds react to their dusty-sweet feather scent. Birds regularly molt scented feathers which conservation staff have collected for me to use in odor experiments. If Kakapo can detect feather scent, the next step will be to uncover whether humans can decipher the meaning of the odor signal and whether it can facilitate the breeding and management of this critically endangered, national treasure.
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