March 2016

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)