*A short and snappy headline*
At less than two meters in length, the African dwarf crocodile (Osteolaemus tetraspis) is the smallest true species of crocodile in the world and can be found in tropical and sub-Saharan West Africa from Senegal to Uganda. They are highly cryptic, rarely leaving the water of the remote swamps they occupy. However, the expert Zookeepers at Crocodiles of the World in Brize Norton, UK have managed to captive breed these cryptic crocs for over 14 years, learning much about their natural history in the process.
Osteolaemus
There are two species of “dwarf” crocodiles (not to be confused with the dwarf caimans of South America that belong to the Alligatoridae family), O. tetraspis and O. osborni. The former is more widely distributed, whereas the latter is found only in the Congo Basin.
Adult males will rarely exceed 1.8 – 2m in length; females tend to be around 1.5 – 1.6m in total length. The colouration is dark: grey or black. As with all crocodilians, the eye colour tends to blend with head colour for camouflage, so these guys have dark brown, almost black, eye colour as well.
The body is robust, compact in this species, and heavily armoured. The rear feet have reduced webbing than in larger crocodilian species. The head and jaws are stocky and powerful, with a crushing bite designed for their prey of freshwater crustaceans, small animals, frogs, fish, crabs etc.
Colin Stevenson, Head of Education at Crocodiles of the World told Exotics Keeper Magazine: “In the swamps and wetlands of the West African home for this species, small pools, streams and lagoons are preferred over broader and deeper water bodies. Many of these will be in almost closed-canopy forests, so the water is dark – ideal for this cryptic species. Much has been made of some populations that have found a relatively undisturbed habitat within cave systems, but this is not the normal habitat for the species. Crocodilians are adaptable, though, and as long as there is water, an ability to thermoregulate and food available, they can cope.”
“In captivity, we try to mimic this to an extent. As a zoo we design enclosures to suit the species first of all, then to permit safe and suitable access for keeping staff, and thirdly we factor in visitors – who have paid to see some animals! So, our Osteolaemus enclosure is intentionally less brightly-lit, and we feature branches and leaves that extend out over part of the enclosure. We house African cichlids in the pool as well. There are darker, more secluded sections within the pool and on the land area so that the crocodiles can feel more secure – a taste of what they’d experience in the wild!”
Conservation
The African dwarf crocodile is considered Vulnerable by the IUCN, although it was last assessed in the 1990s. Therefore, the species could be in a far more perilous position today as agricultural and infrastructural development has continued throughout Africa’s equatorial countries.
Colin continued: “Like most animals that are threatened to any extent these days, loss of habitat or quality of habitat is a major factor. In parts of their range, Dwarf crocodiles are also prime targets for the bush meat trade. Their small size makes it relatively easy for them to be caught alive and then carried to the bush markets to be slaughtered. Overfishing in many areas can reduce prey species, but these crocodiles remain quite widespread. Because threats to the wild populations remain, the species is listed as Vulnerable. Over the coming years, as the dwarf crocodile complex of species or subspecies is redefined taxonomically, it’ll be interesting to see how the various populations are assessed regarding conservation status.”
Species and speciation
Because Osteolaemus are so adaptable, there have been some rather miraculous stories of specific populations inhabiting surprising locations. One specific population of O. tetraspis in Gabon has been recorded living in cave systems almost entirely isolated from other populations. The only access to these underground cave networks is through a 7m deep shaft and yet, the caves supported a healthy population that differed from the nominate forms. The “cave crocodiles” were typically larger than other members of the species, almost entirely blind and stained orange. It is thought the colouration comes from a chemical attack on the skin. These crocodiles are also a few percent genetically distinct from other crocodiles, suggesting that they have been isolated for thousands of years. Furthermore, rather than predating on crabs, frogs and shrimps like “normal” O. tetraspis, the cave crocodiles eat a diet primarily made up of bats, crickets and a large amount of algae. Although this case may represent a purely miraculous case of adaptability, the huge range of these animals across a poorly-studied and often inaccessible part of the world suggests there could be many more Osteolaemus species or subspecies to describe.
Keepin’ crocs
“The fundamental approach to husbandry for all crocodilians is fairly standard” explains Colin. “For each species, we may tweak the temperature and lighting regimes according to what we consider is ‘normal’ for them in the wild, but again, there is some cross-over between species from similar tropical areas.”
The exhibit is around 20 square meters. Two-thirds of the floor space is water and the water depth at its deepest point is around 80cm.
Temperatures within the enclosure fluctuate to replicate tropical climes. These range from nighttime lows of around 26°C to daytime highs of 35°C during the hottest part of the year, with a humidity range of 70-90%. They are also provided with full-spectrum lighting and specific UVB access, but Colin admits “We don’t expect them to use it as much as, Nile crocodiles (Crocodylus niloticus), for example.”
The basking rig is comprised of a 1.5kw shortwave heater coupled with an 8x 54w T5 Unit that uses 4x 14% tubes, and 4x plant growth tubes. With this basking setup, the keepers can achieve temperatures of 34 – 45°C with a UVI maximum of 2.7. Water temperature will go from 26 – 30°C throughout the year.
The African dwarf crocodiles at “Crocs of the World” co-habit with Malawi cichlids, cuckoo catfish, and long-fin tetra. They are fed once weekly, but this may be reduced slightly in cooler months, depending on the animals’ overall body condition. The team offers a variety of food items such as crayfish, fresh fish, rodents, poultry (mainly chicken or quail), Rabbit, and venison when available, food items will usually be fed whole.
Breeding crocodiles
Breeding crocodilians in captivity can be a difficult process that requires a lot of careful consideration. Not only do most species produce 20+ eggs per clutch, but their large size means that most collections cannot house a vast number of animals and thus the choice when pairing two individuals is limited.
Colin added: “Breeding of the species within European zoos is overseen by studbook keepers who will recommend pairings of animals to maintain high genetic diversity within the European zoo population. They may also recommend certain pairs are specifically not bred due to an excess of crocodiles from the pairing already within the zoo community. Exchanges between European and American zoos will sometimes be considered, just to introduce ‘new blood’ into both communities.”
For the past 6 years, Crocodiles of the World have been donating all Osteolaemus eggs to an ongoing project with researchers at the Natural History Museum/Imperial College. This is because zoos rarely require 20+ new juveniles that hatch with every clutch. “The other important point is that with crocodilians, there is temperature-dependent sex determination (TSD)” Colin added. “This simply means that it is the temperature at which the egg develops that will determine whether the young are males or females. We can therefore incubate for males or females by setting the temperature within our incubators accordingly.”
A zoo might need some young crocodiles for use in an education program, or in the case of Crocodiles of the World, have requests from other zoos for certain species or certain sexes of these species (another zoo may, for example, want some male crocs to pair up with some females that they already have). Crocodiles of the World can therefore look at incubating eggs of certain species depending on their own needs and those of other zoos within the region.
Colin continued: “What we don’t want is to be left with a large number of growing crocodiles – and they live for 50+ years! To continue breeding each year and hatching more and more crocodilians without plans in place would be highly irresponsible! Similarly, any young crocodilians we hatch out for use in our education programs will need to have a plan for when they outgrow these education programs.”
The incubation process
Crocodilians have long been bred in captivity and understanding the science of incubation is something that professionals have refined over many years to now achieve extremely high success rates. Clare Wilkie, Researcher at Crocodiles of the World told Exotics Keeper Magazine: “We generally choose to artificially incubate crocodilian eggs so we can closely monitor them to ensure they keep within an appropriate temperature and humidity range throughout the incubation period but they can certainly be incubated in a more ‘natural’ setup within their nests too.”
The African dwarf crocodiles at Crocs of the World maintain a nest site year-round, but it is reported that the actual nesting typically begins in Spring, with egg-laying to follow in early Summer. This process usually spans April through June. Artificial incubation lasts around 85 days, but “natural” incubation also follows a similar pattern, as the keepers at Crocs of the World discovered in XXX.
“Expectant females are highly adept at detecting the most suitable temperature zones for nesting” added Clare. “However, in zoos, the choice of nest site will always be somewhat limited to the available parameters of the given environment. A few years ago, a clutch of eggs was left to incubate within the nest of our female Osteolaemus and some of those eggs did hatch successfully. Jolie, the mother did very well in demonstrating that strong maternal care that crocodilians are well known for, assisting the hatchlings from the nest to the pool and continuing to display protective instincts as they grew.”
“Currently at Crocodiles of the World, when we plan to re-introduce hatchlings into the parents’ exhibit, we’ll remove the clutch of eggs but leave the nest in place. This allows the female to continue her nest-guarding instincts and when we pop the hatchlings back in, those parental impulses naturally kick in. This method allows us to reach those optimal incubation conditions and gives us the added benefit of monitoring the hatchlings for a few weeks to make sure they are healthy and strong before introduction.”
Crocodilians as pets
Crocodilians are fascinating animals that, to some, make enticing pets. Although not “commonly kept” in the UK, some species of crocodilians will occasionally become available. The Exotics Keeper survey, which has only captured a small percentage of keepers and kept animals, has documented three different crocodilian species kept in the UK. The most popular of which, are those that are dubbed “dwarf” crocodiles.
Clare concluded: “The ‘dwarf’ status of some species of crocodilians can understandably give the public perception that these animals will remain small throughout their lives, and therefore somewhat easier to manage. However, some dwarf caiman, such as the Schneider’s dwarf caiman, can occasionally exceed two metres in length!”
“Two metres of any species of croc is a powerful animal that can do substantial damage if handled inappropriately. Anyone that has worked with the ‘smaller’ croc and caiman species will likely believe that they are some of the more assertive and boisterous of the crocodilians… certainly with the biggest attitudes!”
“When the misconception that dwarf species remain small is paired with the resilient reputation of crocodiles, this can in a few rare cases, see crocodilians receive less-than-optimal care. However, it should be recognised that some private keepers demonstrate exceptional standards of crocodilian care that should be strived towards!”