Biology Reference
In-Depth Information
showed that over a period of two months, the individuals that stored the labelled seeds
were about five times more likely to recover their items than were other birds in the same
group that had stored non-labelled seeds.
Whilst this result neatly shows that the storing bird benefits from its own hoarding
behaviour, the demonstration that memory is, at least in part, responsible for this
benefit comes from laboratory experiments. In a pioneering study, David Sherry
(Sherry
et al
., 1981) used the fact that information from the right eye in birds is
stored largely in the left hemisphere of the brain, and vice versa for the right eye. This
is because the visual pathways almost completely cross over at the optic chiasm.
Sherry allowed marsh tits (
Parus palustris
) in an aviary to store seeds in moss trays
with one eye covered, and retrieve their stores after an interval of up to 24 hours,
either with the same eye covered, or with the eye cap switched to the other eye. The
birds' performance at retrieving seed dropped dramatically when the eye cap was
switched, suggesting that information stored in the brain is crucial for successful
retrieval (Fig. 3.8).
The results of this and many other experiments showed that food storing birds
have a remarkable spatial memory, including the demonstration that Clark's
nutcrackers can remember where they have hidden their food after 9-10 months
Individuals
recover their own
stores
Spatial memory in
food hoarding
birds
(b)
100
(a)
Hoard
Recover
80
Same:
60
40
20
Switch:
0
Time
Visits
Fig. 3.8
(a) A schematic of the experimental design used by Sherry
et al
. (1981). The
birds stored and retrieve food with one eye covered by a little plastic eye cap. In the
treatment called 'same', the cap was on the same eye for storing and retrieval, but in
the 'switch' condition the eye cap was changed between storage and retrieval of food.
During retrieval, the birds searched for seeds that they had stored 24 hours earlier in
moss-filled trays on the floor of an aviary. (b) The percentage of time and of visits made
to quadrants of the moss trays with stored seeds during recovery, when searching with
the same eye (pale blue) and the other eye (dark blue).
