October can be an exciting time to be looking for birds in Cornwall. A couple of species have crossed my path these last few weeks which have made me consider the journeys they have undertaken to get here. Both are barely the size of a ping-pong ball which makes their travels even more remarkable. The first of this diminutive duo has stopped me in my tracks on several occasions this last month, whilst pursuing our beloved cirl buntings. A little patience and quiet observation has rewarded me with some truly fantastic views of a bird that I never tire of seeing – firecrest – a bird that shares the title of smallest European bird with the closely-related goldcrest. For those that have seen one I’m sure you would agree with me that they are a little gem. Boldly marked about the head with black and white stripes topped off with a fiery crown, they never fail to look anything less than immaculate, as they busily glean insects from the underside of leaves. A regular visitor they may be at this time of year, they have, nevertheless, undertaken a significant over-sea crossing to get to us from where they breed in Continental Europe.
The other species has an even more impressive story to tell. Breeding across Siberia, its usual winter destination is to be found in India and south-east Asia. However, each autumn several hundreds of these little waifs make land fall on the east coast of Britain, from where many continue west to reach us here in Cornwall. Greyish-green above and off-white below the yellow-browed warbler superficially resembles the more familiar and larger chiffchaff, apart from its prominent pale wing bars and line above the eye. Often unobtrusive as they feed in the canopy, they more often than not give away their presence by bouts of emphatic calling. And so it was on such an occasion at the start of October that yellow-browed warbler was added to our garden list.
But why should a bird that should be on the other side of the world reach us here with such regularity? Bird migration is a truly fascinating subject constantly throwing up new stories to amaze and confound us. The reason for why this particular species should turn up in such numbers is not fully understood, but could be based on a theory called reverse migration. All species of migratory bird move between regular breeding and non-breeding areas. However, in all populations there will be individuals whose sense of direction is totally at odds with the majority and will lead them to end up in areas outside their typical range. Reverse migration largely afflicts young, inexperienced birds – those that are undertaking their first migration from where they were born to where they will spend the winter. Unfortunately, it is highly probable that for the vast majority of individuals these wayward journeys will end in their demise as food supplies fail to sustain them for the winter. However, for those yellow-browed warblers that survive, this may be seen as a pioneering strategy, from where new wintering areas will be claimed.
Most migratory birds do, of course, have a well-built navigational system to rely on. The proof is all around, from witnessing returning swifts to our eaves to wintering swans to our wetland refuges. For sheer numbers of birds it is the post-breeding, or autumn migration, that can offer the biggest spectacle as populations are swollen with the newly-recruited mass of juveniles.
To call it autumn migration is something of a misnomer however, as there are several species whose breeding strategies lead to parts of their population returning south from as early as mid-summer. Even before their eggs have hatched, the females of some Arctic-nesting waders for example, like green sandpipers and spotted redshanks, can both leave their breeding territories as early as mid-June, to leave the rearing of the chicks to the males. Compared to spring migration, the return leg is a far more protracted event too. The same level of precision that constrains spring migrants to arrive on the breeding grounds at just the right time, in order to maximise breeding efficiency, is not felt by autumn migrants.
Millions of birds cross over the UK at this time of year in their desire to reach areas where food supply and weather conditions are more favourable than if they were to remain resident. Though much in decline now, our home-bred starlings are joined by overwhelming numbers from mainland Europe in autumn, that perform spectacular pre-roost flying displays at many sites across the country. Our wetlands too provide sanctuary for huge numbers of waders, ducks, geese and swans from Europe, Russia, Greenland and Canada.
Birdwatchers in the UK are very fortunate. Though we often have to endure inclement weather, the geographical position of our countries mean that we sit at a cross roads of many flight paths of migratory birds originating from all points of the compass. Add to this the occurrence of accidentally occurring vagrants and the possibility of some interesting ornithological juxtapositions can take place. At renowned migration hot-spots like Shetland and the Isles of Scilly for example, the occurrence of Asiatic migrants alongside those from southern Europe or even America is not unheard of. And being a collection of relatively small islands also means that we can witness impressive movements of several species of seabirds that skirt our coastline in transit to distant, northern breeding colonies or remote, oceanic, winter destinations.
So, in the approach to winter, with dwindling day light and the prospect of cooler temperatures, it’s reassuring to know that we can expect to welcome a whole host of migratory birds from foreign places, for whom our shores represent respite and sanctuary –