Wildlife Newsletter for the Township of Dalkey
February / 2017 - Michael Ryan
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Male Blackcap – was he born in Germany? Photo: M. Ryan

 

   Many people will be familiar with Blackcaps, handsome, robin sized birds from the warbler family, the male light grey with neat black cap on his crown while the female’s cap is light brown. Lovely singers when they arrive as migrants in the spring but also regular winter visitors to gardens where
they feed on berries and bird food with apples being a particular favourite of theirs. Thankfully they are a species of birds that have been doing very well with Birdwatch recording an 18% rise in population of breeding birds between 1998 and 2013 and blackcaps being noted 43% of gardens in winter. It has been known for a number of decades that the blackcaps found in winter are a different population from the ones that arrive in spring.
   These winter birds visiting our feeders at the moment will return to Eastern Europe to breed in the spring while at the same time the blackcaps that will be singing in Killiney wood in the summer will be returning to us from southern Europe and North Africa. Moving office recently I came upon a few sheets of paper I’d saved which a friend had sent in 2003. This friend was actively involved in trapping blackcaps to gather information about them for Professor Stuart Bearhop whose letter supplied the following information. In December 1961 a cat in Dublin caught an unlucky blackcap that had been ringed on its breeding ground in Austria the previous summer. More conclusive proof was found about blackcaps wintering in the UK and Ireland in the early 90s when German scientist,
Professor Peter Berthold and his colleagues went to England during the winters from 1988 - 1990 and caught 40 wintering blackcaps.

   They brought them back to Germany where they held them till the following autumn and when the time came for them to migrate they studied what direction they were orientating themselves towards, which meant basically, what direction the birds were hopping in. All the British birds orientated themselves in a north westerly direction towards the UK while blackcaps that had bred in southern Germany would orientate themselves in a south westerly direction facing towards Iberia and North Africa. Professor Stuart Bearhop concentrated his research on studying stable carbon isotopes in the birds. This is where my friend Tom came in as, being a licensed bird ringer, he was qualified to trap blackcaps from which he would then take toenail and feather samples as well as very carefully extract a tiny drop of blood from the top of their leg before releasing them unharmed. When examined in a laboratory the stable carbon isotopes in the samples will reveal where the birds were born as isotopes change geographically as a result of biological and environmental processes. The isotopes were revealing the geographical origin of the food the birds had eaten as well as measuring the element of hydrogen in the isotopes which varies at different latitudes. The research proved conclusively that blackcaps wintering in Ireland were birds that had been born in Eastern Europe.

A fluffed up male Yellowhammer near
Broadmeadow Estuary at Swords

   But why did these birds start coming here in the first place? Milder winters, gardens with lots of natural food such as berries and also the increasing popularity of food being left out for birds has made it much easier for them to survive our winters. But probably the main reason is that they don’t have to migrate as far back to their breeding ground decreasing all the risks and energy involved in a long journey. The birds urge to migrate is triggered by day length and, because of our higher longitude, days will be getting longer here two weeks earlier than they would if the birds were wintering in southern Europe so the birds wintering here will get to the best territories earlier, using less energy on the way which can be dedicated to raising more young who themselves will subsequently spend winter here.
    A few years ago BirdWatch Ireland HQ began receiving lots of phone calls and emails about strange birds with bright orange heads that had been visiting gardens around Ireland. These colourful individuals were usually seen among flocks of sparrows and starlings and in fact that’s what they were and their dramatic plumage was a result of them visiting an exotic garden plant. We are used to plants being pollinated by insects and even by the wind, but New Zealand Flax uses another method: it is pollinated by birds. The tubular flowers produce a rich, sweet nectar that many birds find irresistible. As they stick their beaks down into the flowers to feed, a small brush-like appendage dusts the tops of the birds’ heads with brightly coloured pollen, staining it a vivid orange or red colour. When they move on to feed from another flax flower, these birds bring the pollen with them, helping the plant to reproduce. Evidently this female blackcap photographed in our garden had also acquired a taste for flax nectar and the brown cap on her crown was enhanced by some bright pollen face powdering.