Rubber-necking the rare Rothschild Giraffe

The giraffe (Giraffa camelopardalis) is of course a familiar and unmistakeable animal - it is however much less common than often imagined. It is split into a number of subspecies (up to nine, depending where taxonomic boundaries are placed) and even the most common, the Maasai giraffe G. c. tippelskirchi numbers no more than around 40,000 individuals in the wild. Several subspecies number no more than a few hundred, one of which, the Rothschild giraffe G. c. rothschildi has an estimated wild population of less than 650 (all in protected areas of East Africa) with almost as many kept in zoos around the world (including Marwell's conservation programme where I took these photos, although I have seen them wild in the Lake Baringo area of Kenya - it is sometimes known as the Baringo giraffe). They are readily identifiable from the coat colour/pattern, especially the pale 'socks' due to a lack of pattern on the lower leg.

Rothschild giraffes at Marwell - a surreal sight in southern England!

Given the small population size, and ongoing threats such as habitat loss (e.g. encroachment by human settlements), widespread poaching, and possibly hybridisation, this subspecies was added as Endangered on the IUCN Red List in 2010. It is also a poorly understood subspecies with no major research being undertaken on it prior to the ongoing Rothschild's Giraffe Project which aims to look at the behaviour and ecology of wild populations, in particular, ecological/habitat requirements, group dynamics, factors affecting behaviour, social structure, herd formation and relatedness, and from all of this, knowledge about how to formulate effective conservation plans (if you'd like to donate to the project, you can do so here).


Like all giraffes, both sexes have short blunt horns called ossicones (formed from ossified cartilage and fused to the skull) - these contain blood vessels and may be involved in temperature regulation. Males compete by engaging in 'necking' behaviour - this starts by rubbing and pushing, and can develop into full-blown contests as males swing their heads at each other and try to land blows with the ossicones. If you ever get the chance to see this, it's amazing - like a huge game of conkers.

Their necks are of course their best-known feature - with just the usual seven cervical vertebrae, each is about 30cm long and they have ball-and-socket articulations for flexibility. Proportionally, newborn young have short necks with most of the elongation happens after birth, otherwise giving birth would be problematic. When upright, the neck is supported by the nuchal ligament and large muscles which create the small hump seen at the base above the shoulders. When bending down to drink or graze (which also means splaying or bending the legs), the network of veins and arteries called the 'rete mirabile', plus valves in the jugular veins, prevent excessive blood flow to the brain. These are just some of the circulatory adaptations that allow the giraffe to function with such as long neck - its heart rate (about 150 beats/minute) is high for a large animal, its heart weighs around 11kg or more generating blood pressure about twice that in humans, and the skin of the lower legs is thick and tight to prevent too much blood pooling there.

Rothschild giraffe bending down to graze - note the splayed front legs.

I could go on about the bizarre anatony of the giraffe, but I won't - instead, why not have a look at the excellent 'Inside Nature's Giants' TV programme (videos are on Youtube) based on dissections by specialists in their field. It's amazing I can assure you!

Fascinating toxic frogs

I'm moving away from my usual topic today by looking at a species that is neither British nor invertebrate - the green and black poison arrow frog Dendrobates auratus. Poison arrow/dart frogs (they have several non-scientific names) are familiar to many people because of their toxicity and bright colours, but what is actually known about them?

Dendrobates auratus showing green and black colouration.

Well, first of all, although there are around 175 species of arrow/dart frogs (all in the family Dendrobatidae), only 3 are known to be used to coat blowpipe darts with poison, and none of these are in the genus Dendrobates. So, we know that the common name is not an accurate description - good start! Now onto a little background info.

Found in humid lowland and submontane forest and secondary vegetation up to about 1,200m altitude, D. auratus is native to Central America (Costa Rica, Nicaragua & Panama) and NW Colombia and, although many dendrobatids (like many amphibians worldwide) are rare and/or decreasing, this species is not currently threatened in the wild, being rated as of 'Least Concern' by the IUCN. There are also some feral populations in Oahu, Hawaii following a release of around 200 frogs in 1932 as an attempt to control non-native insects - these bred successfully and their descendents persist in the island's mountains and valleys (McKeown 1996). It is a highly variable species with at least 15 distinct colour forms known in the wild - as well as the typical green shown above, there is yellow, largely black, largely brown and the rare blue which is known from the Pacific side of Panama, but threatened with extinction due to clearance for agriculture, which fragments the habitat, though the species as a whole can live around humans (e.g. in parks, gardens and rubbish dumps (Heselhaus 1992, Ostrowski 2009). Being small (c. 20-40mm depending on form) and brightly coloured, tt is a popular pet among keepers of exotic herpetofauna and over-collection may be an issue, although there is a thriving captive breeding trade supplying much of the demand.

It is a semi-arboreal species, conducting much of its activity in trees up to some tens of metres above the ground but descending to the ground to travel between trees as it can not jump between them. Climbing is aided by pads at the ends of its toes (visible in the photo above). Females lay clutches of 3-13 eggs on leaf-litter which the male guards (Heselhaus 1992); they hatch after about two weeks and the male carries tadpoles to stagnant water in a tree-hole, leaf axil of a bromeliad, or small ground-level pool (van Wijngaarden 1990). The tadpoles feed on protozoans and rotifers, metamorphosing after 39-89 days, with sexual maturity being reached in 6-15 months, and a life-span of at least 6 years in captivity (Zimmermann & Zimmermann 1994). Females compete for males, attempting to monopolise them and being known to destroy the eggs of rivals (Summers 1989). If you would like to hear a brief recording of their call, go here.

Although not the most poisonous of dendrobatids, it is toxic enough to make a human unwell with skin glands producing an alkaloid derived from the ants that form much of the wild diet (Caldwell 1996). This reduces the risk of being attacked by predators such as theraphosid spiders AKA tarantulas (Gray et al. 2010), although some of the development of toxicity (e.g. in different popualtions, and captive-bred individuals fed a wild diet) are not fully understood.

So, to finish, why did I decide to look at this species? Well, it is a charismatic species and makes a change from my long run of invertebrate posts. I am also a member of Hampshire Conservation Volunteers - our logo is a frog so we adopted a D. auratus (now named 'Den Bates') at Marwell Wildlife and I wanted to know more about it - if you like this idea, the yellow and black D. leucomelas is still available for adoption...

Mate-guarding in Dendrobates auratus

References

Caldwell, J.P. (1996). The evolution of myrmecophagy and its correlates in poison frogs (Family Dendrobatidae). Journal of Zoology (London) 240(1): 75-101.
Gray, H.M., Kaiser, H. & Green, D.M. (2010). Does alkaloid sequestration protect the green poison frog,
Dendrobates auratus, from predator attacks? Salamandra 46(4): 235–238.
Heselhaus, R. (1992). Poison-arrow Frogs: Their Natural History and Care in Captivity. Blandford, London.
McKeown, S. (1996). A Field Guide to Reptiles and Amphibians in the Hawaiian Islands. Diamond Head Publishing, Los Osos, California.
Ostrowski, T. (2009). Dendrobates auratus.  [accessed 13/08/2012].
Summers, K. (1989). Sexual selection and intra-female competition in the green poison-dart frog, Dendrobates auratus. Animal Behaviour 37(5): 797-805.
van Wijngaarden, R. (1990). Enkele klimaatgegevens en waarnemingen in de biotoop van de gifkikkers Phyllobates vittatus en Dendrobates auratus. Lacerta 48(5): 147-154.
Zimmermann, E. & Zimmermann, H. 1994. Reproductive strategies, breeding, and conservation of tropical frogs: dart-poison frogs and Malagasy poison frogs. In: J.B. Murphy, K. Adler and J.T. Collins (eds). Captive Management and Conservation of Amphibians and Reptiles. Society for the Study of Amphibians and Reptiles, Ithaca (New York). Contributions to Herpetology Volume 11, pp. 255-266.