According to a team of biologists led by Dr Vladimir Dinets from the University of Tennessee, certain species of crocodiles are able to climb trees as far as the crowns despite lacking any obvious morphological adaptations to do so.

Dr Dinets and his colleagues examined previous studies and made new observations of crocodiles in Australia, Africa and North America.

They found that at least four species – the American crocodile, Australian freshwater crocodile, Central African slender-snouted crocodile and Nile crocodile – climbed trees, usually above water, but how far they ventured upward and outward varied by their sizes.

On many occasions, the biologists observed American crocodiles (Crocodylus acutus) up to 1 m long lying on aerial roots and low branches of mangrove trees during the day. Such observations were made in Santa Rosa National Park, Costa Rica, in Lago Enriquillo, Dominican Republic, in Isla de Salamanca National Park, Colombia, and Everglades National Park in the United States.

The team also observed Australian freshwater crocodiles (Crocodylus johnstoni) climbing steep riverbanks on many occasions, and even attempting to climb chain-link fence up to 1.8 m tall.

They observed Central African slender-snouted crocodiles (Mecistops cataphractus) up to 2 meter long basking on fallen trees over river courses both during the day and at night in Gabon.

The scientists also observed a 2-meter-long Nile crocodile (Crocodylus niloticus) basking on a tree in the panhandle region of the Okavango Delta, Botswana, which then dropped into the water as the observers passed it in a boat. The branch was approximately 0.5 m above the water surface. The crocodile likely climbed onto it from the point where it dipped into the water nearer to the bank.

One of the researchers observed juvenile Nile crocodiles basking on tree branches less than 1 m above the water in Mahango Game Reserve, Namibia, in South Luangwa National Park, Zambia, and in Liwonde National Park, Malawi, always during the daytime.

“Climbing a steep hill or steep branch is mechanically similar, assuming the branch is wide enough to walk on. Still, the ability to climb vertically is a measure of crocodiles’ spectacular agility on land,” said Dr Dinets, who is the lead author of a paper published in the journal Herpetology Notes (full paper in .pdf).

The crocodiles seen climbing trees were skittish of being recognized, jumping or falling into the water when an approaching observer was as far as 10 meters away. This response led Dr Dinets and his co-authors to believe that the tree climbing and basking are driven by two conditions: thermoregulation and surveillance of habitat.

“The most frequent observations of tree-basking were in areas where there were few places to bask on the ground, implying that the individuals needed alternatives for regulating their body temperature,” said Dr Dinets, who in 2013 reported another surprising crocodile characteristic – the use of lures such as sticks to hunt prey.

“Likewise, their wary nature suggests that climbing leads to improved site surveillance of potential threats and prey.”

“These results should be taken into account by paleontologists who look at changes in fossils to shed light on behavior. This is especially true for those studying extinct crocodiles or other Archosaurian taxa,” Dr Dinets concluded.

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Vladimir Dinets et al. 2013. Climbing behaviour in extant crocodilians. Herpetology Notes, volume 7: 3-7