Street life
Question: Thousands of animals are killed on our roads every year, so road
kills must exert a selective pressure on animal populations. Is there any
evidence that animals are developing road sense?
Answer: Despite the increase in traffic, over the past few years I have seen
far fewer dead hedgehogs on the roads. I鈥檝e also observed that hedgehogs in our
garden are less inclined to roll up when disturbed; they are much more likely to
get up on their toes and run away. So it鈥檚 my belief that increased traffic and
road kills have selected for more extrovert, longer-legged and faster-running
hedgehogs.
John Coppinger
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Amersham, Buckinghamshire
Answer: In areas with many roads, the hedgehog has lost the tendency to roll
into a ball at the first sign of danger and runs away instead.
Gavin Whittaker
Heriot, Midlothian
Answer: Thirty years ago, whenever I met a hedgehog it would curl up and wait
for me to go away. Now it sees me first and runs.
J. R. Bibby
Kenilworth, Warwickshire
Answer: There certainly appear to be adaptive effects on the behaviour of
some game birds. In nature, they fly low and fast if flushed from cover, then
they flare (zoom sharply up) to put themselves out of reach of leaping foxes or
cats.
With the reduction in other predators, populations that are used to hunters
with shotguns tend not to flare, because they are most easily shot while
flaring. Where highways are a major cause of mortality, however, birds seem to
be selected for flaring, thus avoiding non-leaping, non-shooting vehicles.
Jon Richfield
Somerset West, South Africa
Answer: Over the past 20 years or so, while I have been driving at night I
have noticed a significant increase in the number of flying insects that choose
to vanish from view in near-vertical dives.
Most of my night driving is on slow, rural roads on the Lizard peninsula in
Cornwall. Speed is limited to about 60 kilometres per hour and the light traffic
allows me to use headlights on main beam. This combination may allow some
night-flying insects, moths in particular, time to reach the ground, where the
probability of death from an oncoming car is significantly decreased.
It鈥檚 possible that those preserved by this behaviour pass their habits on to
their offspring and gain the evolutionary advantage.
C. J. Harris
Helston, Cornwall
Answer: Some do and some don鈥檛. Galahs (Cacatua roseicapilla) have
become common birds in the suburban areas of south-east Queensland. Five years
ago they were well represented in the local mix of road kill; today they are
rarely killed by cars.
They like to feed at the sides of the road and, if disturbed, fly away from
cars, whereas they used to fly across the path of oncoming traffic.
Mark Neath
Queensland
Despite much anecdotal evidence like that above, are there any scientific
studies on how animals learn to change their behaviour to avoid 鈥渢raffic
accidents鈥�? We asked Richard Forman of Harvard University, a landscape ecologist
who designs roads that help animals live in the same habitats as cars. He told
us that nobody has yet written the definitive paper on how quickly animals learn
to avoid roads, or indeed if they learn at all. However, they can learn to avoid
particular zones in their habitat that might be harmful to them.
For example, frogs in Ontario have been shown to avoid a new road. But there
is no evidence that this is because they realise they will be killed there; it
seems more likely that they avoid the road because it鈥檚 too noisy. Frogs are
known to steer clear of areas with more noise than their usual habitats. So
while they treat a road as an 鈥渁voidance zone鈥� there鈥檚 no conclusive evidence
that they have learnt to avoid a particular danger.
Tony Clevenger, a wildlife consultant for Parks Canada, has studied animals
in the Banff National Park that need to cross roads to lead their normal
lifestyles, says Forman.
On the newly built Trans-Canadian Highway, Clevenger found that if an
underpass or a bridge is built to allow the animals to cross safely, they take
time to learn to use it.
Wolves and female grizzly bears took an average of four years before they
learned that the bridge was safer than the road. (Male grizzlies have a wider
territorial range, and so didn鈥檛 come into contact with the same patch of road
and bridge as often as the females.)
Forman says that this is evidence that wolves and female grizzly bears can
learn a behaviour pattern given time, although more data needs to be collected.
Studies like these do not, of course, look at the effect of selective
mortality. If hedgehogs vary in their tendency to run or curl into a ball when
facing danger, then decades of busy roads may have had an impact.
It鈥檚 probably not a serious enough topic to attract a research grant, but we
would really like to know the answer.
Given that different populations of hedgehogs (Erinaceus europaeus) vary
greatly in their exposure to traffic and that some populations have been
separated for a long time (European hedgehogs were first introduced into New
Zealand more than a century ago), it shouldn鈥檛 be too hard to study. Are there
any volunteers?鈥擡d
This week鈥檚 question
The numbers game: If you add up all the digits of a number and keep on adding
the resulting digits until you are left with a single digit, then if the
original number is divisible by 3, so is the resultant digit. Thus for 129, 1 +
2 + 9 = 12, 1 + 2 = 3. Or 81, where 8 + 1 = 9. Conversely, if the original
number is not divisible by 3, then neither is the resultant digit. Thus for 131,
1 + 3 + 1 = 5.
I have written a program that tested this rule up to 1 billion and found no
exceptions. I also saw that as the original number increased (and, of course, if
it was divisible by 3) the single-digit result increased by 3 as well: 3, 6, 9,
3, 6, 9 ad nauseam.
What is going on? Has anyone proved this for all numbers? It doesn鈥檛 seem to
work for any other prime.
Chris
By e-mail, no address supplied