Archive for the ‘Mammals’ Category

A recent review paper by Zafir et al on the status of the Sumatran rhinoceros, Dicerorhinus sumatrensis, makes for rather depressing reading. The Sumatran rhino is currently listed as Critically Endangered by the IUCN (click here for an explanation of what this means), and Zafir’s review of current research suggests that there may be just 216 adult rhino left in the wild.


The Sumatran rhino is the smallest rhino species and is rather more hairy than its African cousins. It has two horns and lives in tropical rainforest, eating leaves. Although previously found throughout South-East Asia, its population is now restricted to reserves in Peninsular Malaysia, Sumatra and Borneo and it is the most endangered rhino species on our planet. Zafir’s review shows there have been large drops in the rhino populations in many reserves over the last 20 years. In Sumatra’s Kerinci-Seblat National Park, for example, there were an estimated 28 rhinos in 1995, but by 2007 the Sumatran rhino was deemed extinct in this reserve, while in 1995 Taman Negara National Park in Malaysia was a stronghold with 44 rhino, but extensive photo-trapping in 2004 didn’t produce any rhino photographs and track encounter rates were low, suggesting this population has also dramatically decreased.

 Fig 1 from Zafir et al, showing Sumatran rhino distribution.
1 Bukit Barisan Selatan National Park

2 Way Kambas National Park
3 Danum Valley Conservation Area
4 Tabin Wildlife Reserve
5 Royal Belum State Park
6 Taman Negara National Park
7 Endau Rompin National Park
8 Gunung Leuser National Park
9 Kerinci Seblat National Park.

 Poaching remains one of the main threats to the survival of the Sumatran rhino, with 1kg of horn selling for $45,000. A similarly large threat, however, is the effect of small population size – unfortunately, once a population is reduced it can enter a phenomenon known as the ‘Allee effect’, essentially a vicious cycle where the fact that the population is small increases its chances of getting smaller and going extinct through chance events.


For example, entirely due to chance there may be a larger number of male rhinos born one year, say a 2:1 skew instead of the normal 1:1 ratio. In a large population this skew would have little effect – if the offspring are 20,000:10,000 then there are still plenty of females around. In a small population though this could be catastrophic – if only three offspring are born that year we now have two males and only one female, and this can affect the long-term prospects of the population. In the case of the Sumatran rhino, these ‘stochastic’ (random) events would also be exacerbated by their long gestation and dependency period of calves – rhino usually only have one calf every three years. Another example is that as a population decreases, it gets more difficult to find a mate and to reproduce. In addition, inbreeding and lack of genetic diversity can also have an enlarged detrimental effect in small populations. These combined factors can result in birth rates too low to replace the population, and so the population will gradually diminish to extinction.


The good news is that Zafir et al think the Sumatran rhino can be saved, and they outline the strategies that need to be concentrated on to do so. These include moving (‘translocating’) individuals in isolated populations (that are unlikely to be large enough to be self-sustaining) into a semi captive sanctuary in Sumatra. Here the rhinos can be monitored closely and males and females can be introduced at the best time for reproduction, hopefully maximising reproduction rates. A similar sanctuary has been established on Borneo. The second main strategy is to increase anti-poaching measures for those reserves that do have good rhino populations, as well as greater judicial enforcement when poachers are caught. We need to keep those rhino of breeding age alive to reproduce and build up the populations. These methods will entail considerable funding, although as the authors point out, no more money than was recently paid for an auctioned comic book;  the alternative is yet another species vanishing forever as we watch from the sidelines.



AWA Zafir et al 2011. Now or never: what will it take to save the Sumatran rhinoceros Dicerorhinus sumatrensis from extinction? Oryx 45(2): 225-233

 Further Info
International Rhino Foundation
The Rhino Resource Centre
Animal Info
Ultimate Ungulate 

Allee Effect:
The Encyclopedia of Earth
Endless Forms


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This fortnight’s photo(s) of choice are a set of night shots by photographer Martin Dohrn that I spotted on the BBC Wildlife Magazine website. He’s taken some really interesting thermal images and beautiful after-dark shots of African wildlife that give an unique view of life in the bush. Check them out here.

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Interesting news articles on the BBC’s website today discuss animals with extraordinarily long life-spans, including a lobster that can live to age 85 and a jellyfish that is essentially immortal, and how time-lapse photography has revealed how emperor penguin huddles function to keep all the group members warm at -45 degrees C. Well worth a read.

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On May 4th, a red-crested tree rat, Santamartamys rufodorsalis, showed up at an eco-lodge in Columbia. What was more surprising than usual about this animal sighting was that this species was last seen in 1898 and was thought to be extinct! The rather charming rodent stuck around for an impromptu first-ever photo-call, before disappearing back into his cloud forest home.

Red-crested tree rat (photo thanks to Lizzie Noble)

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Asian elephant (thanks to Kabacchi)Behaviourally, wild elephants perform many actions that suggest cooperation among their herd, such as looking after other mothers’ calves, helping herd members out of mud and other sticky situations, and collectively protecting the herd’s calves against predator attacks. Proving elephants cooperate with each other experimentally, however, is difficult – not least because elephants are huge and potentially dangerous animals to be doing experiments with!

In this week’s PNAS, Joshua Plotnik and his fellow researchers devised a clever experiment with Asian elephants, Elephas maximus, at the Thai Elephant Convservation Center. Adapting a test previously used with chimpanzees, the researchers provided pairs of elephants with a challenge – a table with food on it lay behind a net just out of the elephants’ reach, but a rope had been curled around the table and one end of this rope lay in front of each elephant. If just one elephant pulled their rope end, the rope pulled free of the table and so neither elephant got the food, however, if both elephants pulled their rope simultaneously, the table was pulled towards them and they were rewarded by being able to reach the food.

The research demonstrated that not only did the elephants quickly learn this task, they also learned to wait by their rope for their partner to be released before pulling on the rope (up to 45 seconds after their own release and access to the rope).  In addition, two elephants devised their own method for getting the food; one would wait for his partner to be released – but he waited by the partner elephant not by the experimental apparatus. The second worked out that she could stand on her end of the rope and the other elephant would then do all the pulling!  Finally, in control trials, where one elephant’s rope was out of their reach (i.e. the task was impossible), the elephants gave up before, or soon after, their partner gave up, suggesting that they recognised it was their partner and not just tension on the rope that they required to complete the task.

Although this behaviour perhaps does not sound that impressive to us humans, it is in fact pretty unusual for the animal kingdom. Humans are masters of cooperation with peers, but most other animals cannot coordinate their behaviour to work as a team to gain a reward (examples of animals that can include apes, dolphins, and domestic dogs). In similar experiments to this, for example, rooks (Corvus frugilegus) did not wait for their partner if the partner’s release was delayed. The elephants’ ability to learn this type and level of cooperation between two individuals, therefore, puts their cooperation skill level on a par with chimpanzees.


JM Plotnik, R Lair, W Suphachoksahakun, FBM de Waal. 2011. Elephants know when they need a helping trunk in a cooperative task. PNAS 108(12): 5116-5121

Further Information

Asian elephants:
The Encylopedia of the Earth
National Geographic

Cooperative behaviour:
Game theory and the Prisoner’s Dilemma
Cooperative behaviour meshes with evolutionary theory – SciencDaily
How did cooperative behaviour evolve? – Science 

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This fortnight’s highlight is a collection of photos by the Smithsonian Institute taken by scientists using camera-traps. Camera-traps are an important tool in zoology research nowadays. Essentially a camera-trap is an infra-red (or, less usually, pressure pad) triggered camera (sometimes pair of cameras) set up across a trail or at a place where the target animal is likely to pass (such as a scent-marking point, salt lick, or waterhole) that takes a photo automatically when an animal breaks the infra-red beam (or stands on the pressure pad). They allow scientists to see rare and cryptic (camouflaged) animals, to make population estimations of animals in dense habitat such as rainforests where you don’t usually see the animals, and to prove that certain species are present or using particular habitats. And as a nice bonus, you get some interesting and beautiful photos of some of the rarer and more secretive animals on our planet.

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Following the Madagascar theme of the currently running BBC documentary (Wed BBC2 8pm), today’s photo is a video clip of one of Madagascar’s unique animals, the streaked tenrec Hemicentetes semispinosus.

Tenrecs are Madagascar’s equivalent of a hedgehog or a shrew. Among the streaked tenrec’s strange quirks are the fact that it keeps its family together by communicating using specialised quills (see the clip below) – and it needs to, because tenrecs have the highest number of offspring in one litter of any mammal… up to 32 babies all at once!

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