Tool use in crocodylians: crocodiles and alligators use sticks as lures to attract waterbirds

By Darren Naish

In recent years it has – I really, really hope – become better known that non-bird reptiles (turtles, lizards, snakes, crocodiles, alligators and so on) are not boring dullards, but behaviourally complex creatures that get up to all sorts of interesting things. Play behaviour, complex social interactions, gaze recognition, pair-bonding and monogamy, social hunting, speedy learning abilities and good memories have all been demonstrated across these groups. And another interesting and unexpected bit of complex behaviour has just been published. It’s so interesting that I feel compelled to write about it today. It concerns what seems to be tool use in crocodiles and alligators.

As described by Dinets et al. (2013), Mugger crocodiles Crocodylus palustris in India and American alligators Alligator mississippiensis in the USA have both been observed to lie, partially submerged, beneath egret and heron colonies with sticks balanced across their snouts. Birds approach to collect the sticks for use in nest building and… well, let’s just say that it doesn’t end well for the birds. If the crocodylians really are using the sticks as bait to attract their bird prey, this is tool use, since the sticks are objects that are being employed for a specific function.

The occurrence of sticks on the crocodylians is not random: stick-displaying behaviour was most frequently observed both in those crocodylians living at rookeries and was exclusively observed during the egret and heron nesting season, being most frequent in late March and April (when the egrets and herons are working hard to find sticks) (Dinets et al. 2013).

The possibility that stick-displaying behaviour results from a random association between rookery-frequenting crocodylians and floating sticks is unlikely since floating sticks are extremely rare in the pools concerned, especially at the time of year concerned (partly this is because the local trees – baldcypresses and water tupelos – don’t shed twigs, but also because the nesting birds rapidly remove floating sticks for nest-building). Therefore, deliberate collection and employment of sticks by the crocodylians seems most likely (Dinets et al. 2013): it seems that they are practising baiting behaviour, whereby predators use objects in order to get potential prey to closely approach and hence become easier to catch. Even better, they are seemingly only practicing this baiting behaviour during a specific part of the year.

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http://blogs.scientificamerican.com/tetrapod-zoology/2013/11/30/tool-use-in-crocs-and-gators/