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Behaviour and Physiology of Crocodiles

Dr Ross Dwyer discusses how the world’s largest living reptile copes with challenges of living in the water, and hunting at the water’s edge.
In this section you will learn about the fascinating world of estuary crocodiles. Hi, I’m Dr. Ross Dwyer, and I’m a specialist in animal movement ecology at the University of the Sunshine Coast Australia. Now for the past 12 years, I’ve been working with Australia Zoo, our neighbours here on the Sunshine Coast to catch, track and observe a population of wild estuarine crocodiles up in far north Queensland, Australia. The insights we’re learning from our long term behaviour study are providing unique insights into the amazing world of these top predators. Of the 24 extant species of crocodilia, the estuarine crocodile is the largest and most widely distributed, ranging from Sri Lanka in the west, and eastern Australia in the east.
Salties are known to be the least social and most aggressive of crocodilians. They’re also thought to be the most tolerant of saltwater, found regularly in freshwater and in marine environments. Indeed, some individuals have been observed swimming hundreds of kilometres out to sea, and there’s been recorded attacks on humans in Australia’s Great Barrier Reef. Estuarine crocodiles have a number of adaptations for living at sea. This includes a large tail for propulsion, integumentary sense organs along the body and particularly around the head and mouth that detect movements of predators and prey under the water.
Eyes and nostrils positioned on the top of a dorsally flattened head are perfect for stalking prey along the riverbank, and osmoregulatory organs, including lingual salt glands, the cloaca and kidneys allow them to maintain homeostasis along a broad salinity range. Like sea turtles, female crocodiles return to land in order to build nests. But unlike turtles, crocodiles have extended maternal care where females guard ness and care for their young following hatching. Our studies have shown that female estuarine crocodiles can travel up to 70 kilometres to preferred nesting sites. With the distance travelled and the duration spent protecting nests be larger and longer in older, more experienced crocodiles.
Parental care is really rare among reptiles, and is a trait much more commonly associated amongst birds. Indeed crocodiles are more closely related to birds than they are to other reptiles, both sharing a common ancestor and belonging to the subclass Archosaura. They also share other behavioural traits and anatomical features with birds. Not only are they good parents, but both crocodiles and birds are highly vocal and have complex social systems. There’s also a striking similarity between the respiratory organs of birds and crocodiles. The hyper-efficient breathing system of birds is also somewhat present in crocodilians.
Both groups boast uni-directional airflow, which is a more efficient system to that adopted by mammals and other reptiles, where gases move throughout the airways in a single direction both during inhalation and exhalation. Like birds, crocodiles have a four-chambered heart, where crocodiles have a unique valve that actively controls blood flow between the lungs and the rest of the body. By fixing tracking devices to animals and tracking their movements using a network of satellites and instream logging devices, we have shown that, like birds, crocodiles are amazing navi-GATORS! Tracking devices have shown us that adult males can travel hundreds of kilometres each year to find potential mates or to access preferred wet season feeding grounds.
In translocation experiments, tagged crocodiles travelled up to 400 kilometres (a mean of 20 kilometres per day) from areas where they were translocated to their original capture locations. And to do so they took advantage of ocean currents and tides to facilitate this travel, effectively ‘surfing the wave’ to get back to their original capture location. This demonstrates an acute navigation ability beyond simple familiarity with the region, and Has implications for management actions that promote human safety in crocodile country. This efficient breathing system and advanced social and movement behaviours may have evolved in a common archosaur ancestor of crocodilians, birds and dinosaurs.
So by studying the behaviour and physiology of crocodiles, it can give us unique insights into what the behaviour and physiology of dinosaurs might have been that’s not available in the fossil record.

Everyone knows what a crocodile looks like, that they can grow to enormous sizes, and that they sometimes eat people. However, few are aware that they are also devoted mothers, have complex social systems, that they are amazing navigators, and the surprising fact that that crocodiles are actually more closely related to birds than they are to lizards!

In this video we will explore how dedicated field studies are revealing fascinating insights into the secret lives of crocodiles. We discuss the behavioural and physiological traits that make crocodiles exquisitely attuned to life underwater, and how traits that are shared between crocodiles and birds can provide unique insights into that of a common archosaur ancestor (e.g. the dinosaurs) that are not available in the fossil record.

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Life Below Water: Conservation, Current Issues, Possible Solutions

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