I am writing this column on St. Valentine’s day. Traditionally, this is the day that birds
find a mate for the forthcoming breeding season. Of course, the birds know nothing of a Roman
martyr who died 18 centuries ago, nor of his influence over the greetings card
industry or floristry, nor even of the concept of February let alone what 14
means. So they have been happily going
about the business of pairing off for many days now. Our bird feeders and the surrounding
undergrowth have been host to much wing shaking and tail flicking by the local
avian community. Dunnocks in particular
are very obvious in their courtship rituals, though at the moment we have three
dunnocks going round displaying to each other, so there’s still a decision to be
made there. It was nice to see a pair of
long-tailed tits on the feeders this week.
At this time of year long-tailed tits leave the noisy mobs they are
usually part of and just go round as pairs.
I am told that the long-tailed tit’s nest is a remarkable flexible
construction made from spiders’ webs and moss, but sadly I have never seen one. We seem to have had a lot more birds on the
feeders generally, which perhaps reflects the scarcity of more natural food
sources at this time of year.
One relatively rare visitor this week was a male
blackcap. Blackcaps are normally
regarded as summer visitors, arriving in April a little ahead of other
warblers, but it has been found that winter sightings reach a peak about
mid-December. It’s tempting to blame global
warming for this phenomenon by which milder winters allow summer visitors to
stay here all the time. Though global
warming may play its part, this turns out not to be the case. Our summer visiting blackcaps arrive in about
April from their wintering grounds in Africa or Southern Spain, where they
return to in late August. The population
that we see in the winter arrive in September or October from Central Europe to
which they return in spring, arriving a couple of weeks ahead of the returning
African migrants. It is thought that
this gives them an advantage for food and nesting resources over those
returning from the South.
I don't have a photo of an Arctic Tern, this moody shot of a Common Term will have to do |
This change in migration habits adds even more mystery to
the subject of migration. How does a
bird the size of a blackcap decide that it will be better off flying west
rather than south? And how does it know
that Sussex will be better than Hungary or Romania? Another migration that defies explanation
cropped up on television recently – that of the arctic tern. This elegant bird spends our summer breeding
in the Arctic, (its southern breeding limit in Britain is around North Wales)
and then another southern hemisphere summer feeding in the Antarctic! (10,000 miles or so, as the crow flies!) Recent studies have shown that populations
breeding in the Netherlands fly 56,000 miles on their annual migrations – more
than twice the distance round the world.
Clearly they don’t take the direct route.
One migration mystery that has been cleared up recently is
that of the European robin. Yes, it does
migrate – some robins don’t migrate at all, but some UK robins fly south to
Spain, and some Scandinavian robins fly south to the UK. The mystery that has been cleared up is how
they navigate. It turns out that they
can detect the angle that the earth’s magnetic field makes with the ground. This doesn’t give them an idea of north or
south, but rather how far they are from the pole or the equator. (Something we could detect with an
inclination compass.) How it does this
is to do with a protein called cryptochrome found in the robin’s eye, quantum
entanglement and superposition and there is not space here to explain it even
if I fully understood it. But if you are
interested it is all properly explained in a fascinating book about quantum biology
– well I found it interesting, anyway.
(Life on the Edge by Jim Al-Khalili and Joe McFadden, published by Black
Swan)