At the time of writing I’ve just settled at my desk with the sounds of the African savannah and the Norfolk fens still ringing in my ears. As I sauntered through Dulwich Park over the lake boardwalk I was confronted by a male Reed Warbler, Acrocephalus scirpaceus busily singing away, high on the top of a reed with his scurrilous, yet enchanting, chattering voice. In ecology the `Field of Dreams` hypothesis stems from the Kevin Costner film of the same name where he famously quoted `Build it and they will come`; create the appropriate habitat for a species and they will eventually occupy that habitat. In the case of the Reed Warbler, mature phragmites, reed grasses, are their favourite haunt as they provide the requisite insectivorous food source along with concealed nesting opportunities. Measuring five inches in old money and weighing the equivalent of two teaspoonfuls of sugar, these birds traverse the Sahara from their West African wintering grounds, travel through Southern Europe and reach the U.K. at the end of April and through May. To fully appreciate and marvel at that Bradley Wiggins type effort I urge you to take a teaspoon and measure out the sugar ... see unbelievable! More exactly named the Eurasian Reed Warbler, to differentiate it from the 38 other family members, the U.K. attracts two other closely related species the Sedge Warbler Acrocephalus schoenobaenus, and the much rarer and sadly declining Marsh Warbler, Acrocephalus palustris; Acrocephalus translating as pointy head. The Sedge Warbler provides its own amazing endurance story: it increases its weight by over 50% and flies back through Europe over the Sahara to West Africa non-stop, a distance of over 3000 kilometres! The Reed Warbler`s journey is a much more leisurely affair afforded by a more generalised diet, punctuating the flight back with several feeding stop-overs.
Climate change seemingly has had a positive effect on the Reed Warbler in the U.K. as the generally warmer weather has allowed a wider more northerly range for the species, laying dates have become earlier creating more chance of two broods, and earlier growth of reeds is potentially increasing nesting opportunities whilst at the same time decreasing predation risk. In East Anglia the Reed Warbler has another form of predation to contend with, the Cuckoo, Cuculus canorus. Favouring the Reed Warbler as a host species the Cuckoo lays an egg, which mimics the colour and markings of the warbler’s egg, in the warblers nest and leaves the Reed Warbler parents to fledge a very hungry and large chick.
For our Reed Warbler we must hope that a partner is found and that a territory or two evolves in the next few years. Until then I’ll luxuriate in my own field of dreams where the sound of Reed and Sedge Warblers is punctuated by the evocative cry of the Cuckoo.