17.02.2021: At adult size, American alligators have no natural enemies while the closely related spectacled caimans are smaller and have to avoid predators. However, small hatchlings of both species might be expected to show similar levels of exploration in order to avoid predators. Researchers at the Vetmeduni (Konrad Lorenz Institute of Ethology) and theUniversity of Lincoln (UK) conducted comparative studies with American alligator and spectacled caiman hatchlings and found that the alligators are much more likely to explore their surroundings. The researchers suggest that the behaviour reflects the strength of maternal protection. The study results were published in “Animal Cognition”.
While many adult crocodilians (crocodiles, gharials, alligators and caimans) are the apex predators in their habitat, their offspring are all tiny right after hatching. They are at risk of being eaten by almost any carnivore around. Therefore, one could expect hatchlings of any crocodilian species to be shy and move around as little as possible in order to avoid become lunch. However, a new study found that young American alligators and spectacled caimans behave very differently just a month after hatching. The alligators are more active and explore more of their surroundings than the caimans.
The research, conducted at "Crocodiles of the World", the only zoo in the UK specializing in keeping crocodilians, put American alligator and spectacled caiman hatchlings in unknown environments and presented them with unknown objects. The alligators moved around much more than the caimans in all conditions and approached the unknown objects closer than the caimans. The movements of the animals were coded automatically using a colour tracking software specifically developed for this study. “We used automatic coding because it allows us to catch even very small differences in behaviour”, says Stephan Reber, the article’s the first author. The observed behavioural tendencies of the hatchlings are very reminiscent of those of the adults. “Adult American alligators are rather self-assured and confident, while adult spectacled caimans are, in comparison, a bit jumpier and more easily spooked”, explains Reber.
Hatchlings of the two species are probably equally susceptible to predators as they are very similarly sized. But they do not to face the world alone. All crocodilians are guarded by a parent (usually the mother) for a considerable amount of time after hatching. The strength of that protection depends on the adult size of the parents. “American alligator mothers have no natural enemies in their habitat and can protect their hatchlings effectively against any predator. On the other hand, adult spectacled caimans have many predators, including cougars, jaguars, and green anacondas”, says Reber. Therefore, American alligator hatchlings can afford to be more explorative under their mother’s watchful eye, while spectacled caimans probably behave more inconspicuously to avoid attracting attention even if they are guarded.
“The findings of this study are exciting as they have important conservation implications”, says Anna Wilkinson, the final author of the study. Several crocodilian species are endangered in the wild and one way to increase their population size is to release captive-bred juveniles into the wild. If the endangered species is a large crocodilian and at the top of the food chain, the juveniles should be allowed to grow to a larger size prior to release as they might have a lower natural predator avoidance. On the flip side, spectacled caimans are an invasive species in the natural range of other crocodilians, including the American alligator, and one reason for their success could be a higher survival rate of their hatchling because of their stronger tendency to avoid predators.
The article "Early life differences in behavioral predispositions in two Alligatoridae species.” by S. Reber, J. Oh, J. Janisch, C. Stevenson, S. Foggett and A. Wilkinson was published in Animal Cognition.