Milder winters and hotter summers have encouraged species like blackcap, chiffchaff and sandwich tern to ditch their autumn migration south and stay here in Dorset
A few months ago, I wrote about the colonisation of new species to Poole Harbour (and the UK) such as great white egret and cattle egret. Traditionally southern European birds, their populations have spread northward over the last 20 years. Mediterranean style conditions - milder winters and hotter summers – are one of the main divers for this recent influx. However, it’s not just egrets that are choosing to relocate to our shore, several other species are now ditching the long journey south in autumn and staying here instead.
One such species is the mighty blackcap, a robust warbler that spends the summers breeding in woodlands across northern Europe before heading south in September to southern Europe and north Africa. Recent studies have shown that many blackcap from central northern European populations don’t head south at all. Instead, they head west-north-west to southern Britain where they take up residence in urban gardens.
Usually, a shy and retiring bird that prefers to sing high up in the canopy, come winter they become the bullies of the bird table, scaring off any other species that try to muscle in on their fat balls!
It’s suggested that the increased amount of food we are putting out in our gardens and milder weather conditions are the main reason blackcaps are choosing to winter in Britain rather than head south. This also gives them the advantage of a much shorter journey back to breeding sites, so they get the pick of the best territories and nest sites. A smart move.
Another species that now calls Poole Harbour home in winter is the tiny chiffchaff. In early spring their monotonous chiff-chaff chiff-chaff song rings out across nearly every woodland, instead of migrating to southern Europe and north Africa in autumn these leaf green warblers are now over-wintering in their thousands across England.
Unlike the blackcap which are able to switch from insects in summer to fat balls in winter, chiffchaff need a constant insect diet throughout winter. This may sound tricky, but at the right places - sewage works, drainage ditches, sheltered hedgerows - they find an abundance of insect food due to our British mild winters.
Our final ‘staying put’ species is the sandwich tern. Poole Harbour has a population of around 150 pairs that breed on Brownsea during the summer, most then head to west Africa for the winter. However, over the last couple of decades between 5-15 of these elegant birds have been seen feeding along the urban shorelines during the colder winter months. Why some are choosing to stay here, we’re not entirely sure. It could be a breeding strategy, ensuring they get to breeding sites quicker than competitors, or it could simply be that this will become the norm and over time more birds will decide to overwinter in Poole Harbour.
So, when out walking this February, don’t be fooled into thinking summer has arrived early if you see one of these winter strangers.
Click here to find out more about these and other species found in and around Poole Harbour
