Hyena Scent Posts Use Symbiotic Microbe Messengers

Twitter limits human communication to a mere 140 characters. Animals’ scent posts may be equally as short, relatively speaking, yet they convey an encyclopedia of information about the animals that left them.

In the current issue of the
Proceedings of the National Academy of Sciences, a Michigan State University researcher shows that the detailed scent posts of hyenas (Figure 1) are, in part, products of symbiotic bacteria, microbes that have a mutually beneficial relationship with their hosts.

“When hyenas leave paste deposits on grass, the sour-smelling signals relay reams of information for other animals to read,” said Kevin Theis, the paper’s lead author and MSU postdoctoral researcher. “Hyenas can leave a quick, detailed message and go. It’s like a bulletin board of who’s around and how they’re doing.”

Figure 1. A spotted hyena scent marking. (courtesy of Michigan State University)

Interestingly, it is the bacteria in pastes – more diverse than scientists had imagined – that appear to be doing the yeoman’s job of sending these messages.

“Scent posts are bulletin boards, pastes are business cards, and bacteria are the ink, shaped into letters and words that provide information about the paster to the boards’ visitors,” Theis said. “Without the ink, there is potentially just a board of blank uninformative cards.”

Theis, who co-authored the study with
Kay Holekamp, MSU zoologist, studied multiple groups of male and female spotted hyenas and striped hyenas in Kenya.

By using molecular surveys, they were afforded unprecedented views of the diversity of microbes inhabiting mammals’ scent glands. The researchers were able to show that the diversity of odor-producing bacteria in spotted hyena scent glands is much greater than historical studies of mammals had suggested (Figure 2).

Figure 2. Variation in the bacterial communities and volatile fatty acid (VFA) profiles of the pastes of immigrant male, lactating female, and pregnant female spotted hyenas in the Talek clan. (A and C) A plot showing variation in the structure of paste bacterial communities among Talek clan members. (B) A heat map of the mean abundances of the prominent bacteria in the pastes of Talek hyenas. (D) A heat map of the mean percent abundances of VFAs in the pastes of Talek hyenas. From Theis et al. 2013)

The diversity, however, still consistently varies between hyena species, and with sex and reproductive state among spotted hyenas, Theis added. Importantly, the variation in scent gland bacterial communities was strongly correlated with variation in the glands’ odor profiles, suggesting that bacteria were responsible for the variation in scent.

For the current paper, Theis’ team was the first to combine microbial surveys and complementary odor data from wild animals. The studies’ findings leave Theis anxious to return to the field.

“Now I just need to get back into the field to test new predictions generated by this study,” Theis said. “The next phase of this research will be to manipulate the bacterial communities in hyenas’ scent glands to test if their odors change in predictable ways.”

Source: Modified from materials provided by Michigan State University.


Theis KR, Venkataraman A, Dycus JA, Koonter KD, Schmitt-Matzen EN, Wagner AP, Holekamp KE, & Schmidt TM (2013). Symbiotic bacteria appear to mediate hyena social odors. Proceedings of the National Academy of Sciences of the United States of America PMID: 24218592

Orangutans plan and communicate their travel plans

For a long time it was thought that only humans had the ability to anticipate future actions, whereas animals are caught in the here and now. But in recent years, clever experiments with great apes in zoos have shown that they do remember past events and can plan for their future needs. Anthropologists at the University of Zurich have now investigated whether wild apes also have this skill, following them for several years through the dense tropical swamplands of Sumatra.

It turns out that wild male orangutans do plan their travel route up to one day in advance and communicate it to other members of their species (Figure 1). In order to attract females and repel male rivals, they call in the direction in which they are going to travel. Anthropologists at the University of Zurich have found that not only captive, but also wild-living orangutans make use of their planning ability.

Figure 1. Travel maps of wild orangutans. Green arrows show “long calls”. (from van Schaik et al. 2013)

Orangutans generally journey through the forest alone, but they also maintain social relationships. Adult males sometimes emit loud ‘long calls’ to attract females and repel rivals. Their cheek pads act as a funnel for amplifying the sound in the same way as a megaphone. Females that only hear a faint call come closer in order not to lose contact. Non-dominant males on the other hand hurry in the opposite direction if they hear the call coming loud and clear in their direction (Figure 1).

Figure 2. A Orangutan males give long calls to attract females (or repel rival males). Female A perceives a faint call compared to female B, even if they are at the same distance from the calling male, because the male is facing female B. If the male is moving in the same direction as he is calling, female A should move in the direction of the male whereas B need not. (from van Schaik et al. 2013)

“To optimize the effect of these calls, it thus would make sense for the male to call in the direction of his future whereabouts, if he already knew about them”, explains Carel van Schaik. “We then actually observed that the males traveled for several hours in approximately the same direction as they had called.” In extreme cases, long calls made around nesting time in the evening predicted the travel direction better than random until the evening of the next day. Carel van Schaik and his team conclude that orangutans plan their route up to a day ahead.
In addition, the males often announced changes in travel direction with a new, better-fitting long call. The researchers also found that in the morning, the other orangutans reacted correctly to the long call of the previous evening, even if no new long call was emitted. “Our study makes it clear that wild orangutans do not simply live in the here and now, but can imagine a future and even announce their plans. In this sense, then, they have become a bit more like us”, concludes Carel van Schaik.

Source: Modified from materials provided by The University of Zurich.


Carel P. van Schaik,, Laura Damerius,, & Karin Isler (2013). Wild Orangutan Males Plan and Communicate Their Travel Direction One Day in Advance PLOS ONE DOI: 10.1371/journal.pone.0074896

Military Sonar Alters Whale Behavior

Some blue whales (Balaenoptera musculus) off the coast of California change their behavior when exposed to the sort of underwater sounds used during U.S. military exercises. The whales may alter diving behavior or temporarily avoid important feeding areas, according to new research by the Southern California Behavioral Response Study.

Researchers exposed tagged blue whales in the California Bight to simulated mid-frequency (3.5-4 kHz) sonar sounds significantly less intense than the military uses. "Whales clearly respond in some conditions by modifying diving behavior and temporarily avoiding areas where sounds were produced," said lead author Jeremy Goldbogen of Cascadia Research. "But overall the responses are complex and depend on a number of interacting factors," including whether the whales were feeding deep, shallow or not at all.

The scientists tagged the whales with non-invasive suction cups, which recorded acoustic data and high-resolution movements as the animals were exposed to the controlled sounds (Figure 1). 


Figure 1. Examples of behavior changes of tagged blue whales during exposure experiments. The sound exposure periods are highlighted in blue on each track line. The location of the sound source is indicated by the large red circle. (From Goldbogen et al. 2013)

"The tag technology we use offers a unique glimpse into the underwater behavior of whales that otherwise would not be possible," said Ari Friedlaender, a research scientist at the Duke Marine Laboratory.

The scientists found that some of the whales engaged in deep feeding stopped eating and either sped up or moved away from the source of the noise. Not all of the whales responded to the noise, and not all in the same way.

"Blue whales are the largest animals that have ever lived. Populations globally remain at a fraction of their former numbers prior to whaling, and they appear regularly off the southern California coast, where they feed," said John Calambokidis, one of the projects lead investigators.

That area of the ocean is also the site of military training and testing exercises that involve loud mid-frequency sonar signals. Such sonar exercises have been associated with several unusual strandings of other marine mammal species (typically beaked whales) in the past. Until this study, almost no information was available about whether and how blue whales respond to sonar. 

"These are the first direct measurements of individual responses for any baleen whale species to these kinds of mid-frequency sonar signals," said Brandon Southall, chief scientist from SEA, Inc. "These findings help us understand risks to these animals from human sound and inform timely conservation and management decisions."

A related paper published by the same research team in
Biology Letters has shown clear and even stronger responses of Cuvier’s beaked whales (Ziphius cavirostris) to simulated mid-frequency sonar exposures. Beaked whales showed a variety of responses to both real, military sonar in the distance and nearby simulated sonar. What the beaked whales were doing at the time appeared to be a key factor affecting their reactions.

The research was funded by the U.S. Navy Chief of Naval Operations Environmental Readiness Division and the U.S. Office of Naval Research, and appears in the Proceedings of the Royal Society B. 

Source: Modified from materials provided by Duke University.

Goldbogen, JA et al. 2013. Blue whales respond to simulated mid-frequency military sonar. Proceedings of the Royal Academy B, DOI -10.1098/rspb.2013.0657

DeRuiter, S. et al. 2013. First direct measurements of behavioural responses by Cuvier's beaked whales to mid-frequency active sonar. Biology Letters, DOI – 10.1098/rsbl.2013.0223


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Figure 1. An African wild dog (Lycaon pictus). (From Steve Jurvetson/Flickr)

The hypothesis that threats from larger competitors like lions and hyenas limit wild dog population density and distribution has only recently been tested in the field. Hugh Webster, John McNutt, and Karen McComb played lion roars and hyena whoops to 8 packs of African wild dogs and observed their responses. The lion roars were from both male and female lions recorded in other African parks. These roars were presented as single lions roaring or as choruses of 3 lions roaring together. The hyena whoop calls were similarly recorded and presented to the wild dog packs.

Wild dog packs responded to lion roars by standing, facing the direction of the hidden speakers, rearing up on their hind legs to get a better view, and cautiously approaching the source of the roar. In dense habitats, however, the wild dogs quickly retreated (Figure 2).

Figure 2. A bar chart showing the mean time to retreat by wild dog packs’ in response to lion roars in habitats of differing density. (Webster et al., 2012)

Wild dogs responded very differently to hyena whoops (Figure 3). Instead of retreating, wild dog packs generally remained in the same area and eventually dozed off, suggesting that hyenas in the area do not pose a significant threat to the pack.

Figure 3. Wheel diagrams showing the direction and distance travelled by wild dog packs in the hour following playbacks of lion roars or hyena whoops. The playback loudspeaker is located 100 m north of this center point. (From Webster et al., 2012)

Interestingly, wild dog packs did not differ in their response when choruses of 3 lions were presented versus only a single lion roar. In fact, the only variable that explained wild dog behavior was the density of the surrounding habitat. Presumably, wild dogs are at greater risk of ambush by lions in dense vegetation where sight is limited.

These results indicate that lions may limit wild dog packs to areas on the periphery of lion ranges or to areas with less prey where the packs are less likely to encounter lions. As the authors point out, this has important implications for wild dog reintroduction programs. It may be best to avoid reintroductions in areas were lions are abundant.


Webster, H., McNutt, J., & McComb, K. (2012). African Wild Dogs as a Fugitive Species: Playback Experiments Investigate How Wild Dogs Respond to their Major Competitors Ethology, 118 (2), 147-156 DOI: 10.1111/j.1439-0310.2011.01992.x

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Tragic events often have unintended and far-reaching consequences. The destruction of the World Trade Towers by terrorists on September 11th 2001 was just such an event. It goes without saying that there were many consequences for humans, including two wars, increased airline screening, and shifts in the political landscape. But there were also consequences for other mammalian species as well.

Endangered North Atlantic right whales (
Eubalaena glacialis) gather during the late summer on calving grounds in the Bay of Fundy, Canada (Figure 1). A substantial portion of the calving grounds lies in an important shipping lane. Low frequency noise produced by ship engines and propellers travels long distances in water and is believed to interfere with acoustic signaling by whales. Previous studies have shown that right whales alter their vocalizations in response to increased underwater noise.

Figure 1. A map of the Bay of Fundy, Canada showing the Right Whale Conservation Area and the shipping lanes. (From Rolland et al., 2012)

Rosalind Rolland from the New England Aquarium in Boston, and seven colleagues from across the United States, were collecting data on social behavior in right whales in the Bay of Fundy in August and September 2001. When shipping traffic ceased following the events of September 11
th, it presented the researchers with an unintended natural experiment. They realized that they had data that could test the hypothesis that shipping noise directly altered the behavior of North Atlantic right whales.

The researchers collected acoustic data, shipping traffic data, and fecal samples for right whales. The later were used to measure stress hormones (glucocorticoids) produced by the whales. Their results reveal a significant drop in low-frequency background noise in the days immediately following September 11
th when shipping traffic stopped in the Bay of Fundy (Figure 2).

Figure 2. Power spectrum of underwater background noise from 2 days before and 2 days after 11 September 2001. There is a significant decline in low-frequency (< 150 Hz) noise after September 11 when shipping traffic stopped. (From Rolland et al., 2012)

Interestingly, the decline in background noise was correlated with decreased levels of stress hormones in right whales (Figure 3).

Figure 3. (a) Fecal glucocorticoid levels in North Atlantic right whales before (grey boxes) and after (white boxes) 11 September for the years 2001–2005. (b) Significantly lower Fecal GC levels were significantly lower after 11 September only in 2001, when shipping traffic stopped for a few days resulting in a decrease in underwater low-frequency noise. (From Rolland et al., 2012)

This fortuitous study represents the first direct link between shipping traffic noise and stress levels in whales. It suggests that whales congregating in high traffic shipping lanes are chronically stressed by noise pollution.


Rolland, R., Parks, S., Hunt, K., Castellote, M., Corkeron, P., Nowacek, D., Wasser, S., & Kraus, S. (2012). Evidence that ship noise increases stress in right whales Proceedings of the Royal Society B: Biological Sciences DOI: 10.1098/rspb.2011.2429

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