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(b)
(a)
Store
nuts
Store
worms
Retrieve
(i)
0
120
124
hours
Store
worms
Store
nuts
Retrieve
(ii)
0
120
124
hours
Fig. 3.10
(a) A scrub jay at a food storing tray in an experiment to investigate episodic memory. The coloured
blocks provide spatial cues for the bird. Photo © Nicky Clayton. (b) Design of an experiment to test for episodic
memory. In treatment (i) the birds are given nuts to store, then 120 h later they are given worms to store. Four hours
after that, they are allowed to retrieve items. In treatment (ii), the order of storing is first worms, then nuts. From
Clayton & Dickinson (1998). Reprinted with permission from the Nature Publishing Group. See text for explanation.
The evolution of cognition
Nicky Clayton and her colleagues have used the food storing behaviour of western
scrub jays
Aphelocoma californica
in the laboratory to explore the mental capacities of
these birds (Fig. 3.10a). She has investigated three aspects of behaviour that appear to
demonstrate surprisingly complex mental representations.
One study showed that the scrub jays remember what they have stored, and when
and where. This kind of memory for specific events in humans is called 'episodic
memory' and is distinct from 'procedural memory' for learned skills such as riding a
bike or playing the piano. The essence of the experiment was that the birds were allowed
to store two kinds of food, nuts or worms, in a tray, with an interval of 120 hours
between storing episodes. They were then allowed to retrieve both nuts and worms after
another four hours (Fig. 3.10b). Normally scrub jays prefer worms, but worms decay
after 124 hours whilst nuts do not. Thus, if the birds remember what they have stored,
where it is and when it was stored, they should search in the nut part of the tray if they
have stored worms 124 hours before (treatment (ii) in Fig. 3.10b) and in the worm part
of the tray if they stored nuts 124 hours earlier (treatment (i) ). The birds did this, even
when both worms and nuts were removed during the retrieval period, to ensure that
scent or another cue did not give the game away (Clayton & Dickinson, 1998). The birds
appear to have an episodic-like memory.
Clayton's second study investigated 'social cognition': the ability of a bird to behave as
though it could interpret the knowledge of another individual. Dally
et al
. (2006) found
that when a scrub jay had been observed by another individual whilst caching food, it
would, later on when in private, move its caches to new locations, as though it were
aware of the fact that it had been observed and that the observer might pilfer the caches.
Furthermore, the jays re-cached more of their food items when they had been observed
Episodic memory:
what, where and
when?
Social cognition:
recognizing
potential thieves
