Primatology.net

Infanticide and cannibalism are two extreme behaviors seen in primates. Though extreme, the persistence of these behaviors in primates suggest that they are adapted for and had evolved to serve different purposes. Infanticide and cannibalism can be considered as both reproductive and survival strategies. Infanticide has always been associated with males killing off the progeny of former dominant males to make females more sexually receptive and to shorten the birth interval. Cannibalism, on the other hand, is not as sinister as it has always portrayed to be but just a coping mechanism. Ingestion of body parts, usually own offspring, is a response to cope with food scarcity. Lack of food resources would inevitably result in the death of the offspring thus cannibalization returns the caloric investment back into the mother. A new paper by Culot et al. (2011) has documented a case of infanticide and cannibalism in a wild female moustached tamarin (Saguinus mystax).

Moustached Tamarin (S. mystax) from The Bronx Zoo, New York City. Photo from Wikipedia.

S. mystax belong to the Callitrichid family, and like all Callitrichids has an interesting reproductive strategy unlike those of other primate families. Callitrichids form multimale-multifemale group and has a polyandrous (one female, multiple male) mating system. Callitrichids are the only primate family that consistently give birth to twins. The gestation period for S. mystax is 6 months. Usually, only one dominant female is reproductively active and shares offspring rearing responsibilities with multiple males in the group. However, an unstable dominance hierarchy among females might lead to multiple births within the group and will compromise the survivability of both the group and the offspring from stress, less parental investment and lack of food resources.

The researchers were studying how help from male moustached tamarins in the same group and the absence of female competition ensure the survival of offspring when they observed a female cannibalizing an infant. Necropsy and genetic analyses were used to rule out diseases and to determine paternity. They found that the infant has no diseases and did not die from trauma (falling from tree). Instead, it was a healthy infant and was being cannibalized by its own mother.

The mother was seen biting and then eating the head of its own infant during a period when another female was pregnant and gave birth just 1 month later. Before that, the perpetrator had given birth to twins three times successfully when four to five adult and subadult males were present in the group. Although we do not know for certain that the infant was alive when the mother started biting it, our field observations preceding the event suggest it probably was. The possible infanticide case and the two cases of births and early death of the infants occurred while only two to three adult males were present in the group. This could be the second case of maternal infanticide reported in the genus Saguinus and the similar circumstances suggest a common pattern. Culot et al. (2011).

Five common hypotheses proposed by Hrdy (1979) were used by the authors to try to explain maternal infanticide and cannibalism in this scenario. These hypotheses are resource competition, sexual selection, social pathology, exploitation, and parental manipulation.

The resource competition and sexual selection hypotheses were rejected because it was maternal infanticide, and not infanticide from another female. The social pathology hypothesis was rejected because it predicts infanticide restricted in areas that are disturbed by humans. The study group was habituated and had many successful births, therefore social pathology was ruled out. The exploitation hypothesis was also reject because the mother did not kill her infant to exploit its meat. Observation shows that the mother only consumed the brain and parts of the infant’s neck.

The parental manipulation hypothesis was accepted because the authors think that it best explains the scenario. The offspring was not pathological nor did it fell from the tree. Instead, it was a healthy infant that was killed by its own mother. According to Hrdy (1979), victim of parental manipulation does not necessarily have to be defective but also born “at the wrong place in the wrong time”.

The authors concluded that parental manipulation is the best explanation for this possible maternal infanticide scenario. Parental manipulation strategy can happen in a group with poor capacity to raise the offspring from multiple breeding females, birth intervals that are shorter than 3 months, and low infant survival probability due to physical injuries or weakness.

References:

Do you know that fossil primates once roam North America? I didn’t know either so this discovery was a shock and a “d’oh” moment at the same time.

Lingual view (side that touches the tongue) of Mescalerolemur horneri partial mandible.
Scale bar equals 2 mm. Photo from Kirk & Williams (2011).

Anywho … A fossil primate from the Eocene Epoch was discovered in Devil’s Graveyard badlands of West Texas by Anthropologists Christopher Kirk and Blythe Williams. Named Mescalerolemur horneri, this new fossil primate lived about 43 million years ago is a member of the extinct group, adapiforms, that are found all over the Northern Hemisphere. Mescalerolemur looked like a modern-day greater dwarf lemur and weighs about 370 grams.

Interestingly enough, Mescalerolemur are more closely related to Eurasian and African adapiforms than those from North America. Darwinius masillae, famously known as Aunt Ida, was a Eurasian adapiform. Another interesting fact to point out is that Mescalerolemur had unfused mandibular symphysis, similar to those of Strepsirrhines (lemurs, lorises and galagos). The authors posit that this is definitive evidence that adapiforms are more similar to Strepsirrhines than Haplorrhines (humans are Haplorrhines). Kirk &Williams (2011) published their findings on Journal of Evolution: New adapiform primate of Old World affinities from the Devil’s Graveyard Formation of Texas (PDF). You can also read more about the discovery at EurekAlert: Anthropologist discovers new fossil primate species in West Texas.

Originally posted on The Prancing Papio.

On April 13, 2011, The Maryland Zoo in Baltimore announced the birth of an Endangered Coquerel’s Sifaka (Propithecus coquereli) making it one of only 50 individuals found in accredited institutions in the United States.

Coquerel-Sifaka at the Maryland Zoo in Baltimore, Photo: Kristin Abt

Read the press release for more information!

The Duke Lemur Center manages the United States’ Coquerel’s Sifaka population and provides more information about the species: Coquerel’s Sifaka

Long-tailed Macaques (Macaca fascicularis) were able to succeed when faced with a basic numerical test, discovers a team of researchers at the German Primate Center, Goettingen. Researchers Vanessa Schmidt and Julia Fischer developed a basic test where an individual was presented with two plates, each containing a different quantity of pebbles, and where the plate with the largest number of pebbles gave a greater reward. The macaques were able to understand the concept of relative quantities, and choose the correct option at 80%+ success rate.

Although experimentation testing these types of numerical skills are not new, previous studies used edible items where the subject may eat the amount of food on the plate in which they choose – this experiment yielded only a 69% success rate in this study, and showed that the impulsiveness to gain a reward that they could see impaired their judgement when making a choice. Therefore previous studies may have underestimated the animals’ ability.

More information at; BBC – Earth News

Schmitt, V. & Fischer, J. Representational format determines numerical competence in monkeys. (2011). Nat. Commun. 2:257 DOI: 10.1038/ncomms1262.

Last week, I blogged about the semantics of alarm calls in vervet monkeys. This post will focus solely on the ingenious experiment by Robert Seyfarth, Dorothy Cheney and Peter Marler (1980) to test whether vervet monkey alarm calls convey information or if these calls were just an uncontrollable auditory response to predators. Their question was simple; would vervet monkey alarm calls alone elicit different responses?

A vervet monkey. Photo from Wikipedia.

Here’s what the researchers did in the field. They used playbacks of recorded vervet monkey (subjects) alarm calls from concealed speakers. Equal amount of alarm calls for leopard, eagle and snake were used. These alarm calls were recorded from known adult male, adult female and juvenile vervet monkeys in the field. Trials were done when subjects were on the ground and also when they were in the trees. These trials were conducted in the absence of predators to eliminate visual cues from the caller.

Alarm calls were broadcasted in different amplitudes to mimic natural alarm calls. In succession from loudest to lowest amplitudes are alarm calls for leopard, eagle and snake. Subsequently, leopard calls have the lowest pitch while snake calls have the highest pitch. To control for the possible effects of amplitude, the researchers broadcasted alarm calls that do not differ significantly in the amplitudes for all three predators.

Table from Seyfarth et al. (1980). Click on illustration for its original size

The alarm call playbacks showed two types of responses. First, subjects of any sex and age looked at the direction of the speaker and spent more time scanning their environment once an alarm call was made for more than 10 seconds. The researchers believe that they might be scanning for additional cues from the “caller” and the subject’s surrounding.

Second, each alarm calls seem to elicit a distinct response from the subjects. Remember the trials were done when the subjects were on the ground and on the trees? When subjects were on ground, leopard calls were more likely to make them run up into the trees and eagle calls made them look up and run into cover (bushes) Snake calls made them look down. When subjects were on the trees, leopard calls were more likely to make them run higher in trees and to look down. Eagle calls made them look up and sometimes run out of trees. Snake calls made them look down.

From the results, Seyfarth et al. (1980) posit that vervet monkey alarm calls alone do elicit different responses. It’s hard to tease out whether these alarm calls symbolize the predator ”leopard” or a command ”run up tree”. However, we can postulate that these alarm calls are rudimentary semantic signals used to warn other conspecific of impending danger. For those that are not familiar with semantics, it refers to the meaning of a symbol, sign, word or phrase. In this case, vervet monkey alarm calls are semantic signals because it conveys a specific meaning.

Reference:

Seyfarth, RM. Cheney, DL. Marler, P. 1980. Monkey responses to Three Different Alarm Calls: Evidence of Predator Classification and Semantic Communication. Science 210(4471): 801-803.

Originally posted on The Prancing Papio.

Anti-predatory alarm calls are important  for social animals to alert others of approaching predators. Without the presence of “language”, some non-human primates are known to give out different predator-specific alarm calls to alert conspecific. These non-human primates include ring-tailed lemurs (Zuberbühler et al., 1999), white-faced capuchin monkeys (Fichtel et al., 2005), Diana monkeys (Zuberbühler, 1999), Campbell’s monkeys (Ouattara et al., 2009) and vervet monkeys (Seyfarth et al., 1980).

Alarm calls are typically high frequency sounds because these calls are hard to localized by predators. On the other hand, low frequency sounds are easier to localized by predators. Calls that are hard to localized by predators are selected for because conspecific can pick up on the warning but predators cannot identify the location of the caller. If an individual successfully alert its social group of approaching predator yet does not reveal its location, it will significantly decrease the chance of the caller to be detected and increase the chance of its social group to avoid predation.

Here, I will focus on the study of predatory alarm calls in vervet monkey (Chlorocebus pygerythrus) by Seyfarth et al. (1980) in the Amboseli National Park, Kenya. Vervet monkeys are Old World monkeys that range between Eastern and Southern Africa. These monkeys are diurnal and live in closely-knit social groups. They are quadrupedal and are both terrestrial and arboreal. Like all Old World monkeys, vervet monkeys have the characteristic cheek pouches that enables them to forage and store food to be eaten later. Male vervet monkeys have blue scrotal area and a red penis. Males and females are sexually dimorphic, with males slightly larger than females.

Vervet monkeys are known to elicit predator-specific alarm calls. Three well-documented vervet monkey alarm calls are those for leopard, martial eagle and python. Leopard alarm calls are short tonal calls produced in a series of inhalations and exhalations. Eagle alarm calls are low pitched grunt while python alarm calls are high pitched “chutters”. Different alarm calls seem to evoke different responses to individuals that heard the alarm calls. However, the first reaction of a vervet monkey upon hearing an alarm call is to look at the direction of the caller. Looking at the direction of the caller gives them clues as to why the alarm calls were made and also where the caller is facing reveals the direction of the approaching predator. You can listen to these different alarm calls on this site.

As we said before, different alarm calls evoke different responses. Leopard alarm calls would make the monkeys run up into the tree to avoid being ambushed by the leopard. Also, these monkeys would sit on the branches further away from the tree because, even though leopards can climb trees, the branches could not support the leopard’s weight. When an eagle alarm call is given, vervet monkeys would make them look up, run for the nearest bush or both to avoid an approaching aerial attack. Python alarm calls would the monkeys stand bipedally and look down on the ground.

Adult vervet monkeys are more discriminatory when eliciting alarm calls. Infants and juveniles calls however, are less discriminating as they attribute most terrestrial mammals with leopard calls, flying birds with eagle calls and stick-like figures with snake calls (although, compared to infants, juveniles are more discriminant when making alarm calls). In spite of that, adult vervet monkeys seem to elicit eagle alarm calls to different species of raptors and non-raptors (see illustration below). We can infer that adult vervet monkeys attribute eagle alarm calls to birds with the same silhouette as martial eagles. As vervet monkeys get older, they seem to have a better association between predator species and types of alarm calls. Vervet monkeys generally pay more attention to adult alarm calls than those of juveniles or infants.

The study of vervet monkey alarm calls by Seyfarth et al. (1980) laid an important ground work to better understand the complexity of animal communications. By showing that vervet monkeys make different alarm calls to different predatory species, we can posit that vervet monkeys have the ability to categorize different species. The ability to discriminate between terrestrial mammal, flying birds and snake-like objects starts during infancy in vervet monkeys. As they get older, they are better at associating predators with specific alarm calls.

The ability to over generalize during infancy is evident in both vervet monkeys and humans. For example, upon learning the word “dog”, human infants would refer to quadruped mammals they see as “dog”. As the infant grows, so does the ability to associate the semantic meaning of words they learned. However, the acquisition of alarm calls in vervet monkeys is different than the acquisition of speech (language) in humans. Alarm calls in vervet monkeys are instinctual and not learned. Humans, however, have to learn their language. Failing to do so during the “critical period” generally will result in the inability to learn language in later years. Feral child are examples of human infants that lack linguistic input during their critical period of language acquisition.

Most of us interpret animal alarm calls as an uncontrollable auditory response to fear or pain, akin to humans yelping if we had our finger caught in a door. While this is not entirely false, some animal calls actually convey information from the caller to the listener. Seyfarth et al. (1980) posit that vervet monkey alarm calls are actually basic semantic signals or symbolic signals because each alarm calls seem to mean something to these vervet monkeys. While we don’t know if these alarm calls actually mean “leopard” or “run up to the tree”, we do know that it conveys specific information to their conspecific about approaching predators.

I will be blogging Part II of this post later this week, where I will explain in details the experiments done by Seyfarth and Cheney on vervet monkey alarm calls.

References:
Cawthon Lang KA. 2006 January 3. Primate Factsheets: Vervet (Chlorocebus) Taxonomy, Morphology, & Ecology. http://pin.primate.wisc.edu/factsheets/entry/vervet. Accessed 2011 March 9.

Fichtel, C. Perry, S. Gros-Louis, J. 2005. Alarm calls of white-faced capuchin monkeys: an acoustic analysis. Animal Behaviour 70(1): 165-176. doi: 10.1016/j.anbehav.2004.09.020.

Gould, JL. Gould, CG. 1999. The Animal Mind. Scientific American Library.

Ouattara, K. Lemasson, A. Zuberbühler, K. 2009. Campbell’s Monkeys Use Affixation to Alter Call Meaning. PLoS ONE 4(11). doi:10.1371/journal.pone.0007808.

Seyfarth, RM. Cheney, DL. Marler, P. 1980. Monkey responses to Three Different Alarm Calls: Evidence of Predator Classification and Semantic Communication. Science 210(4471): 801-803.

Zuberbühler, K. Jenny, D. Bshary, R. 1999. The Predator Deterrence Function of Primate Alarm Calls. Ethology 105: 477–490. doi: 10.1046/j.1439-0310.1999.00396.x.

Zuberbuhler, K. 2000. Referential labelling in Diana monkeys. Animal Behaviour 59(5): 917-927. doi: 10.1006/anbe.1999.1317.

Orangutan at Sepilok (Photo: Kristin Abt)

A recent article “Fostering Appropriate Behavior in Rehabilitant Orangutans (Pongo pygmaeus)” published online in the International Journal of Primatology discusses research on the behavior of rehabilitant orangutans (Pongo pygmaeus and P. abelii) at the Orangutan Care and Quarantine Centre in Pangkalan Bun, Kalimantan (Indonesian Borneo). Much past research has focused on postrelease behavior of rehabilitated orangutans and on the behavior of wild individuals; therefore, this research is especially timely and useful for the number of centers currently attempting to rehabilitate the ever-increasing number of displaced great apes and other fauna (Descovich et al., 2011).

Orangutans (n=40) in this study included males and females, mass classes ranging from 5 to 25 kg, and good, moderate, and poor health distinctions. Individuals were observed continuously for a period of 5 hours during 3 separate forest excursions each.  A number of behaviors relevant to postrelease success in the forest habitat were recorded (type of locomotion, social behavior, such as play, human caretaker interaction, point of height in tree or on ground, feeding and food choice, grooming, etc.).

Results from this study showed that rehabilitant individuals’ masses were associated with the amount of time spent at the centre. Authors note this finding as a result of the early age of admittance to the centre for most individuals. Further, orangutans in better health spent an increased amount of time consuming food and less time resting than other categories. In terms of locomotion (>30% of overall time), quadrupedal movement in trees was the dominant method (again, with orangutans in better health doing so more often). Individuals who had been at the Care Centre longer spent more time on the ground rather than swinging or other locomotion. As the day in which focal individuals were observed continued, human interaction increased.

As rehabilitation of orphaned individuals is a component of the long-term species survival of orangutans, research regarding the behavior of these individuals is important for increasing the chance of postrelease survival and success. Additionally, as their habitat is lost as a result of a number of conservation threats, land protection is necessary to provide habitat in which the released individuals and their wild conspecifics can live.

Reference

Descovich, K. A., Galdikas, B. M., Tribe, A., Lisle, A., & Phillips, C. J. 2011. Fostering appropriate behavior in rehabilitant orangutans (Pongo pygmaeus). International Journal of Primatology. doi:10.1007/s10764-011-9491-1

Orangutan Foundation International (a 501(c)3 nonprofit organization) supports the work of the Orangutan Care and Quarantine Centre and other crucial efforts to promote orangutan conservation, including land protection, research, and education. Visit www.orangutan.org to donate directly to OFI. If you would like to donate items specifically to enhance the lives of individuals at the Care Centre, visit this wishlist to select items that orangutans, such as those in this study, will greatly benefit from. If you would like to learn more, look for the upcoming IMAX© movie Born to Be Wild to be released in theaters April 8, 2011.

Last October, London Zoo saw the birth of a new baby gorilla? He has since been named Tiny and he’s walking now.

London Zoo's Tiny