THE other day a male blackcap appeared at my bird table and it’s been hanging round ever since.
Twenty-five years ago this would have been a sensational sighting because blackcaps were summer migrants and to see one during the winter was very rare. But nowadays blackcaps are quite common in winter.
I used to think that, possibly as a result of global warming, some summer migrants had just not bothered with the long flight back to Africa and decided to tough it out in Ireland. Surprisingly this isn’t the case. All our summer migrant blackcaps head south in the autumn along with the other warbler species and they’re replaced by winter migrant blackcaps that come here from central Europe.
To have two populations of the same species, one of which is a summer migrant to Ireland and the other a winter migrant, is a unique phenomenon, and also quite a recent one.
It appears that some time towards the end of the last century a group of blackcaps that had bred in central Europe set of in the autumn intending to fly south east to wintering grounds in the Middle East. Something went drastically wrong and they ended up travelling in the opposite direction and landing in Ireland.
Two things happened when they arrived. The first was that the migration instinct switched off because it sensed that the journey was now completed. The second was that the birds discovered that Ireland was quite a viable place to over-winter in.
It’s not uncommon for migrating birds to end up in places that are not their intended destination. Ornithologists call them ‘vagrants’. But something very unusual happened to these blackcaps. In the spring they returned to central Europe and bred. Then, almost as if they’d had their sat-navs re-programmed, they returned to Ireland in the autumn.
The fascinating thing about the blackcap that’s taken up residence in my garden this winter is that it throws some light on these mysteries. It seems as though a migration route can be established in a very short space of time as a result of a successful accident. There also seem to be some remarkable similarities between the way the migratory instinct operates and the way computers and computerised navigation systems operate.
HOLLY (Ilex aquifolium)
Holly is a native Irish tree and one of our few native evergreens. It’s a tree that everyone can recognise, but on taller specimens the familiar prickly leaves are replaced by more normal leaves without prickles on the upper branches which are out of reach of browsing deer. It’s an important tree for wildlife. The berries, which only appear on female trees, provide winter food for birds and small mammals, the leaves provide food for the caterpillar of a lovely butterfly, the holly blue, and the dense foliage provides roosting and nesting cover for many bird species. It tolerates a wide variety of soil types and is very wind-resistant but, rather surprisingly, can be killed by prolonged heavy frost. It’s not as widespread in the country as it once was, probably due to exploitation and export for the Christmas market. In the past it was also gathered as winter fodder for cattle and sheep. The association with Christmas is believed to derive from a pagan tradition celebrating the winter solstice. — Dick Warner
© Irish Examiner Ltd. All rights reserved