Conservation Namibia

http://conservationnamibia.com/blog/b2021-dwarf-giraffe.php

Dwarf giraffe – Seriously?!

By Giraffe Conservation Foundation

29th January 2021

 

 

Research teams from the Giraffe Conservation Foundation (GCF) spend a lot of time looking at giraffe, but two particular giraffe recently caused them to do a double take. In amongst the other giraffe that they regularly monitor in Uganda and Namibia, they found two dwarves!

GCF’s monitoring team in Murchison Falls National Park in Uganda saw their “mini-giraffe” for the first time when he was still a young calf in December 2015, and spotted him again during annual surveys in 2016 and 2017. Meanwhile, another team in Namibia photographed a four-year-old giraffe on a private game farm in 2018 that was still the size of a calf! He was found again during their latest survey in July 2020. Each giraffe (dwarf or not) is identified by its unique coat pattern, so the researchers can follow individuals over time.

Being diligent scientists, the GCF teams do more than just watch the giraffe they find – they measure them using a clever, non-invasive method known as photogrammetry. Once calibrated to different camera focal lengths using objects of known sizes, one can get a fairly accurate measurement of giraffe legs and necks from suitable photographs. This means that the scientists can determine the growth rate of young giraffe and the average height and bone lengths of the giraffes in each population without having to sedate and physically measure any of them.

 

 

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The bones measured by GCF scientists. Figure from Brown and Wells (2020).

 

 

This technique certainly came in handy when studying the two dwarves (the Ugandan was nicknamed “Gimli” after a dwarf from the Lord of the Rings, while the Namibian is known as “Nigel”). Emma Wells, who led the Namibian GCF survey on the game farm notes: “the Namibian farmer had spotted Nigel regularly over the years, it was only after our observations that he realised that Nigel was not a juvenile but a fully gown male giraffe. It is mainly in comparison to other giraffe that his difference in stature becomes obvious.”

Although both giraffe were shorter than usual, different bones seemed to have been stunted in each case. While Nigel had a much shorter phalanx (ankle to hoof) bone than normal (4 cm shorter than the average of 20 cm for sub-adults), Gimli’s phalanx was close to average. The next bone up (metacarpal – ankle to knee), however, was much shorter on Gimli (38 cm) than Nigel (51) cm, and both were well shy of the average 65 cm length. The knee to shoulder bone (radius) on both giraffe was about 20 cm shorter than the average. Nigel’s neck was 24 cm shorter than the average 135 cm, but oddly enough, Gimli’s neck was 11 cm longer than average!

 

 

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Giraffe Comparison. A normal sub-adult giraffe (A) has much longer legs than those found in Uganda and Namibia that display what is known as skeletal dysplasia (B and C). Figure from Brown and Wells (2020).

 

 

“Instances of wild animals with these types of skeletal dysplasias are extraordinarily rare”, observed Dr Michael Brown of the Ugandan GCF team. “It’s another interesting wrinkle in the unique story of giraffe in these diverse ecosystems.”

This strange combination of bone lengths certainly makes dwarf giraffe stand out from the herd, but it has negative implications for their survival and reproduction. It is unlikely that either of them can reach a giraffe’s top running speed of 60 km/h – Nigel even has an unsteady walking gait (see video below). The population of giraffe in Murchison Falls National Park in Uganda experiences low predation rates from lions, while the Namibian game farm has no lions at all, which explains why they have survived this long (although Gimli was last seen over three years ago). But being short in stature probably means that even if he reaches sexual maturity, a dwarf male giraffe is unlikely to have much luck with the ladies.

 

 

The Namibian dwarf giraffe called Nigel has a strange gait due to its shortened leg bones and is unlikely to run as fast as the others in its herd. © Giraffe Conservation Foundation.

 

 

Why these dwarf giraffe appeared in two totally different giraffe populations – so distantly related that they are considered separate species – remains a mystery. The population in Murchison Falls National Park underwent a “bottleneck” in the late 1980s when their numbers dropped to fewer than 80, but a genetic study indicated that levels of inbreeding are surprisingly low. Much less is known about the genetic diversity of Namibian giraffe on private land. However, skeletal dysplasia occurs in about 4 in 100,000 live births in humans, so with only about 111,000 giraffe remaining in all of Africa, we are not expecting to find many more dwarf giraffe.

Dr. Julian Fennessy, Director of GCF, commented – “The fact that this is the first description of dwarf giraffe is just another example of how little we know about these charismatic animals. It is only recently that our research has shown that there are four distinct species of giraffe. There is just so much more to learn about giraffe in Africa and we need to stand tall now to save them before it is too late.”