What do geladas and humans have in common? Apparently, vocal patterns.

T. gelada. Photo: Ron Waddington

They live in very large groups called herds, they primarily graze on terrestrial vegetation, and they roam on large open plains. In more than a few ways, geladas (Theropithecus gelada) are similar to cows. Geladas are more vocal than cows though. They have a diverse range of vocalizations for various behaviors and situations, such as contact, showing submission, aggression, and others (Kawai, 1979; Aich et al., 1990).  The diversity and complex communication exhibited by geladas is one of the reasons this is a very interesting primate species to study.

A new study on their vocal sequences shows that this species of Old World Monkey follows patterns that are similar to humans. As far back as the late eighties, Richman (1987) suggested the geladas use melody and rhythm in ways similar to humans. Now, Gustison and colleagues have shown that the longer the sequence of sounds is that a gelada makes, the shorter the sounds within that long sequence. This is the same pattern observed in humans and is called Menzerath's law. The longer our sentences, the shorter the words tend to be in those sentences.

The authors studied fifty-seven male geladas in the wild and recorded and analyzed over 1000 vocal sequences. In addition to discovering that longer sequences are made up of shorter calls, Gustison and colleagues report that long sequences start with short calls and short sequences start with long calls. Thus, the start of the sequence is an indicator of its overall length. Longer sequences also have faster tempos. Gustison and colleagues state this might be to reduce the possibility of one gelada being "talked over" by another. You can understand how this might be a problem in a chatty species that lives on open plains. If you have a lot to say, you better say it quickly.

Geladas grazing. Photo Alastair Rae

Interestingly, there was no negative relationship between the position of a call and its duration (calls later in the sequence were not shorter). Yet, the proportion of grunts where the gelada was exhaling decreased in longer sequences and the proportion of grunts where the individual inhaled increased. The authors believe this pattern is due to the fact that individuals make grunts with both inhalations and exhalations on the same breath as the sequence lengthens. Once geladas have more than 15 calls per sequence, the majority of their calls have both inhale and exhale grunts and the proportion of inhale and exhale grunts hardly varies.  Thus, respiration and energy demands may constrain gelada vocalizations, and be partially the reason for conforming with Menzerath's law.

This is the first time Menzerath's law has been studied in non-humans. Thus, other animals with expansive vocal repertories, such as songbirds, may also exhibit this law. It is hard to draw conclusions about the evolution of communication in non-human primates and our human ancestors without knowing if Menzerath's law holds true for species that are further separated from humans. For now, we know humans are not unique in adhering to Menzerath's law.  It is possible that this pattern existed before meaningful combinations of vocalizations had evolved. Tests in other species will only serve to improve our understanding of sequences, vocal patterns, and the evolution of language and communication in general.



Links of potential interest:
Menzerath's Law
IUCN page on geladas
YouTube video on gelada chatter

Works cited:

Aich, H., Moos-Heilen, R., & Zimmermann, E. (1990). Vocalizations of adult gelada baboons (Theropithecus gelada): acoustic structure and behavioural context. Folia primatologica, 55(3-4), 109-132.
Kawai, M. (1979). Auditory communication and social relations. Ecological and Sociological Studies of Gelada Baboons, 219-241.
Gustison, M., Semple, S., Ferrer-I-Rancho, R, Bergmann, T. (in press). Gelada vocal sequences follow Menzerath’s linguistic law. PNAS. www.pnas.org/cgi/doi/10.1073/pnas.1522072113 
Richman, B. (1987). Rhythm and melody in gelada vocal exchanges. Primates, 28(2), 199-223.

What you may not have read about the scary decline in Grauer's Gorilla numbers

Cover of the WCS and FFI Report

Over a week ago, a report from Wildlife Conservation Society and Fauna and Flora International hit the press about Grauer's gorillas (Gorilla beringei graueri).  Grauer's gorillas, previously known as eastern lowland gorillas, are one of four subspecies of gorillas. Consuming fruits and vegetation, Grauer's gorillas are the largest subspecies. They are listed as endangered and are found only in the Democratic Republic of Congo (DRC).

They made the headlines, and not just on the science news sources, because the latest data shows their numbers have declined dramatically. Over the past twenty years, Grauer's gorilla numbers have declined by an astonishing 77%, with only 2, 585 animals estimated alive today. Their range has been reduced by 84-93%. If you saw this on the news, you probably also saw that civil unrest and other human pressures are the reasons behind the sudden decline. This is hardly surprising.

What you may have missed are some of the more nuanced details behind these numbers, details that can be found in the report itself, which also covers chimpanzees in the same area. In their report titled, "Status of Grauer's Gorilla and Chimpanzees in Eastern Democratic Republic of Congo: Historical and Current Distribution and Abundance," we learn that increases in agriculture and the availability and use of shot guns caused habitat loss and extinctions of local populations in the 60s and 70s. Surveys done in the 90s also suggested species decline due to expanding human populations and hunting. The late 90s and early 2000s saw these threats exacerbated when refugees from civil war in Rwanda, internally displaced people, and armed groups in the DRC put further pressure on DRC forests and wildlife. This influx of people needed fuel for firewood, land for agriculture, timber, and also hunted wildlife and mined.

The main threats to Grauer's gorillas are hunting for bushmeat and habitat loss due to the spread of agriculture. Hunting practices are related to artisanal mining though. These mines are found adjacent to or even in protected areas, are illegal, and are controlled by armed militias (Kirkby et al., 2015). They allow people an economic opportunity to earn an income quickly and attract people from multiple social classes(Kirkby et al., 2015). Once working at these remote mines, miners rely on bushmeat for food and consume primates and other large mammals(Kirkby et al., 2015). The miners aren't evil people though, as many said they wouldn't hunt bushmeat if alternatives were available and also said they wanted to leave the mining industry.

SMART patrols, reconnaissance surveys, transects, and occupancy surveys were used to determine gorilla decline and show that one of the areas with the highest number of animals, Kahuzi-Biega National Park saw a decline of 87% in gorilla density, and this is with a portion of the Park protected reasonably well. Seven of the eleven sites surveyed through encounter rates show an average decline of 94%. These findings are enough to support raising the IUCN status of Grauer's gorillas to critically endangered.

Occupancy probability model from report. Blue areas
mean high likelihood and red very low likelihood of gorillas

Behind these alarming numbers, a story emerges of people pushed beyond their limits and forced to use the forests available in order to survive. Civil war, changes in government, and general civil unrest gives the DRC its tumultuous historic timeline, the effects of which not only impact people but also the flora and fauna of the region. Some may find it easy to forget, but humans and nature are intricately linked.

You may think you have no connection to this story other than one as an innocent bystander, but the resources mined from the DRC are part of an industry many of us play into. Most of the mines are for cassiterite, gold, coltan, and wolframite. The first is an important source of tin, the second you may be wearing now, coltan is used in electronics such as our cell phones, and the last is an important source of tungsten. Given that mining is one of the main reasons Grauer's gorillas are threatened, chances are many of us are connected to this problem, as uncomfortable as that may make us feel.

Links of potential interest
IUCN Page for Grauer's Gorillas
IUCN Categories and Their Criteria
BBC's Country Profile of the DRC

Works cited:

Kirkby, A., Spira, C., Bahati, B., Twendilonge, A., Kujirakwinja, D., Plumptre, A., ... & Nishuli, R. (2015). Investigating artisanal mining and bushmeat around protected areas. Unpublished report to USAID and Arcus Foundation.

Plumptre, A.J., Nixon, S., Critchlow, R., Vieilledent, G., Nishuli, R., Kirkby, A., Williamson, E.A., Hall, J.S. & Kujirakwinja, D. (2015). Status of Grauer’s gorilla and chimpanzees in eastern Democratic Republic of Congo: Historical and current distribution and abundance. Unpublished report to Arcus Foundation, USAID and US Fish and Wildlife Service.

Bonobos focus on the positives: humans focus on the negatives

Photo: Mark Dumont

A recent study done on captive bonobos (Pan paniscus) reports that these apes focus on images that are of a more positive nature (compared to images of danger or aggression). Using a test designed to understand attentional bias in humans, researchers from various institutions in The Netherlands studied attentional bias in bonobos, our close relatives.

Four female bonobos each completed either twenty-five or twenty-six trials in total over thirteen separate testing sessions. They were briefly shown two images and then a dot appeared on the screen which remained there until the individual tapped the dot. Upon tapping the dot, the individual is rewarded with a food item. In half of the trials, the images briefly shown were of a bonobo in some sort of emotional state, such as pant hooting, playing, or in distress. In the other half, the images were of a bonobo in a neutral state.

By looking at the reaction time, Kret and colleagues (2016) were able to determine that bonobos are more captivated by images of other bonobos that are affiliative or protective rather than images with bonobos in distress or aggression, which has found to be the case most often for humans (Vuilleumier and Schwartz, 2001; Williams et al., 2004; Tamietto et al., 2005; Flaisch et al., 2009).

Images of yawning, grooming, and sexual behavior caught the bonobo's attention the most. Reaction time was longest for yawning, followed by grooming and then sexual behaviors. Yawning is a contagious behavior in humans and also for bonobos (Palagi et al., 2014). Grooming and sexual behavior are both types of behavior that reduce tension (Manson et al., 1997; De Waal, 1997; Crockford et al., 2013).

The increased attention devoted to these social behaviors suggest that they are of greater importance to bonobos than aggressive behaviors or actions associated with a threat. Given that this isn't the case with humans and what captures our attention, this study highlights another intriguing difference between the two species.

Links of potential interest:
Paper in PNAS 
Are bonobos more peaceful than chimpanzees?
IUCN page on bonobos


Works cited:
Crockford, C., Wittig, R. M., Langergraber, K., Ziegler, T. E., Zuberbühler, K., & Deschner, T. (2013). Urinary oxytocin and social bonding in related and unrelated wild chimpanzees. Proceedings of the Royal Society of London B: Biological Sciences, 280(1755), 20122765.

De Waal, F. B. (1997). The chimpanzee's service economy: food for grooming. Evolution and Human Behavior, 18(6), 375-386.

Flaisch, T., Schupp, H. T., Renner, B., & Junghöfer, M. (2009). Neural systems of visual attention responding to emotional gestures. Neuroimage, 45(4), 1339-1346.

Kret, M. E., Jaasma, L., Bionda, T., & Wijnen, J. G. (2016). Bonobos (Pan paniscus) show an attentional bias toward conspecifics’ emotions. Proceedings of the National Academy of Sciences, 201522060.

Manson, J. H., Perry, S., & Parish, A. R. (1997). Nonconceptive sexual behavior in bonobos and capuchins. International Journal of Primatology, 18(5), 767-786.

Palagi, E., Norscia, I., & Demuru, E. (2014). Yawn contagion in humans and bonobos: emotional affinity matters more than species. PeerJ, 2, e519.

Tamietto, M., Latini Corazzini, L., Pia, L., Zettin, M., Gionco, M., & Geminiani, G. (2005). Effects of emotional face cueing on line bisection in neglect: a single case study. Neurocase, 11(6), 399-404.

Vuilleumier, P., & Schwartz, S. (2001). Emotional facial expressions capture attention. Neurology, 56(2), 153-158.

Williams, M. A., & Mattingley, J. B. (2004). Unconscious perception of non-threatening facial emotion in parietal extinction. Experimental Brain Research, 154(4), 403-406.