Rain dance
Question: I鈥檝e noticed that early in the morning, if it has just rained,
seagulls will stamp their feet on the wet grass. What are they up to, and why
haven鈥檛 I seen any other birds doing the same?
Answer: This kind of rain dance is not restricted to seagulls: waders also
like to dance, oystercatchers in particular. Unlike the seagull鈥檚 flat-footed
version of an Irish jig on the spot, oystercatchers perform a dance more like a
reel. They move rapidly in straight lines and circles, then stop and repeat the
sequence over again. Not only can you see the rain dance after rain, but also
during a heavy dew or when snow covering the ground has melted exposing large
patches of grass.
Although the communal rain dance of these birds is entertaining, the gulls鈥�
and waders鈥� motivation is purely practical. The foot stamping vibrations trick
the subsoil worms into believing that it is raining and so they head for the
surface, only to be eaten by the gulls and waders.
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As a boy, preparing for a trout-fishing expedition during dry-weather spells,
we threw buckets of water onto short grass, then rapped the ground in the
fashion of a drummer, with sticks and rods.
Five or six boys could each gather about a quarter of a marmalade jar of
worms, from an area of around 12 square metres, in only 10 or 20 minutes,
without having to do any digging.
Richard Hoseason Smith
Peterhead, Aberdeenshire
Answer: The seagull is charming worms. We saw a wonderful example of this in
Edinburgh, last summer.
The seagull in question was drumming its feet, and had a trance-like
expression on its face. Suddenly a huge worm appeared and was hauled out of the
ground and eaten by the seagull. It then continued its dance.
However, it failed to realise that the Edinburgh Festival was in full swing
and that a piper was skirling nearby. Within moments a huge crowd appeared,
delighted to find something new and entertaining to watch, especially as it made
the bagpipes more bearable.
We tried to explain that the seagull was not dancing to the music, but most
of the onlookers didn鈥檛 understand English. Because the seagull had neglected to
put its hat out, we took advantage of our good fortune, had a swift collection
and retired to the pub.
Susan Hill
Abingdon, Oxfordshire
We are not sure if we approve of the commercial exploitation of dancing
seagulls but we suppose that the bird did at least get its worm . . .
The dancing behaviour seems very widespread and thanks are due to other
readers for observations of worm dances by rooks (Richard Maclaurin, Wiltshire),
lapwing and ringed plover (Andrew Manley, Sussex), red-billed gulls (Gil
Brandeis, Wellington, New Zealand), and olive thrushes (Jon Richfield, Somerset
West, South Africa).
Why do worms move to the surface when it is damp and they detect the
vibration of rain? Most people believe that the worms come to the surface in the
rain because worm tunnels can flood and drown their occupants. But as the trick
works also with birds feeding in estuarine mud we can鈥檛 be entirely sure. It may
be that worms surface in the rain because they are not then at risk of drying
out in the sun鈥擡d.
Dotty bottles
Question: Near the base of every glass drinks bottle, be it for milk, wine or
beer, there is a horizontal row of five to eight raised dots with varying
spacing. What are they for? All of the beer bottles that I have seen, for
example, have different dot patterns, so they are no use to sight-impaired
people.
Answer: The row of dots that is found on the heel of glass bottles is there
as a means of identification for the factory that produced the bottle.
Glass bottles are generally made in very large quantities, often on multiple
production lines and using a number of sets of moulds per line. The subtly
different patterns of dots indicate which machine, line, and mould was used to
produce each particular bottle. These spots are a very precise way of keeping
track of production and help a great deal in the monitoring of quality.
Lorna Miller
Harlow, Essex
This week鈥檚 questions
Food for thought: The brain is an energy-hungry organ, which presumably uses
more fuel the harder it works.
Could thinking hard help a person lose weight? Is reading James Joyce鈥檚
Ulysses an alternative to dieting?
Richard Knight
London
Bathed in light: I am studying the life of a well-known British statesman who
was in the habit of taking something called an 鈥渆lectric light bath鈥� in the
years before and after the First World War. What on Earth was this?
Hugh Cecil
London
Whassat? How can a person tell if a sound is coming from in front or behind
when we only have two ears?
Thomas Wills
London
Sex thought: I have heard many times that 鈥渕en think about sex every 8
seconds鈥�. I am interested to know whether this is based on experimental
observation and, if so, how you would carry out such an experiment.
Andrew Jackson
Institute of Neurology, London