Biology Reference
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solution). Secondly, some kinds of 'intelligent' behaviour may be a specific adaptation to
a particular ecological problem, such as the memory of food storing birds. Thirdly, it
turns out that humans, more often than perhaps we appreciate, use subconscious rules
of thumb rather than conscious calculations. The study by Melissa Bateson of paying
for coffee, which is referred to in Chapter 12, is a good example. Experts in marketing
capitalize on our subconscious biases in manipulating us into buying goods (Cialdini,
2001). Therefore, the Darwinian argument that there should be continuity between the
intelligence of non-human animals and man can be turned on its head by saying that
we are in some ways more like non-human animals than we sometimes recognize.
Feeding and danger: a trade-off
If you watch a squirrel eating chocolate chip cookies in the park, as Steve Lima and
colleagues did (Lima et al ., 1985) you will notice that the squirrel generally comes to
your picnic table, grabs a cookie and retreats to a tree to eat it. If you put out small
fragments of cookie the squirrel will often make repeated sorties to the table and take
each morsel back to the tree to eat it. This is obviously not a very efficient way to eat
food: if maximizing net rate of energy intake or efficiency was the only important factor
for a squirrel it would simply sit on the table and eat pieces of cookie until it was full. One
interpretation of the squirrel's behaviour is that it is balancing the demands of feeding
and safety from predators. It could feed at maximum rate and run a good chance of
being killed by a cat by staying on the table, or it could be completely safe from cats but
die of starvation in the trees. Neither of these is the best solution to maximize survival,
so the squirrel does a mixture of the two. Lima et al . argued that the squirrel should be
more prone to seek safety in the trees while feeding when this involves a smaller sacrifice
in terms of feeding rate. Consistent with this they found that when the feeding table was
close to the trees the squirrels were more likely to take each item to cover. Big pieces of
cookie were more likely to be taken to cover than small ones; they take a long time to eat
and are, therefore, more dangerous to handle out in the open and when handling time
is long the relative cost of travelling back and forth is reduced.
The balance between the benefits of feeding and of avoiding danger is also influenced
by an animal's hunger. On a very cold day in winter, normally shy birds become quite
tame at the garden bird table, presumably because their increased need for food overrides
the danger of coming into the open. Manfred Milinski and Rolf Heller (Milinski & Heller,
1978; Heller & Milinski, 1979) studied a similar problem with sticklebacks ( Gasterosteus
aculeatus ). They placed hungry fish in a small tank and offered them a simultaneous
choice of different densities of water fleas, a favourite food. When the fish were very
hungry they went for the highest density of prey where the potential feeding rate was
high, but when they were less hungry the fish preferred lower densities of prey. Milinski
and Heller hypothesized that when the fish feeds in a high density area it has to
concentrate hard to pick out water fleas from the swarm darting around in its field of
vision, so it is less able to keep watch for predators. This was later confirmed by Milinski
(1984). A very hungry fish runs a relatively high chance of dying from starvation and
so is willing to sacrifice vigilance in order to reduce its food deficit quickly. When the
stickleback is not so hungry it places a higher premium on vigilance than on feeding
Balancing
foraging and
safety
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