International travel may be on hold … but not for our migrant birds

International travel may be on hold … but not for our migrant birds

Young swallows on Fullingpit Meadows, Sudbury, photographed by Adrian Walters

While in the human world international travel is all but suspended, in the kingdom of the birds, species are arriving in Sudbury after journeys of thousands of miles.
The compulsion to take off on epic journeys across seas, mountains and deserts in search of food and territory is one of the wonders of the natural world. Migration is not a behaviour reserved solely for birds – many animals including butterflies and turtles undertake their own incredible odysseys – but on our riverside it is the returning birds – swallows and martins, swifts, warblers and cuckoos – that are most apparent.
It is mind-bending to think that only a month or so ago, the swallows we now see flitting across the common lands taking advantage of the insects kicked up by the cattle, were likely doing the same around herds of buffalo and elephant in South Africa where they spend the winter.
It seems hardly believable that a creature that weighs less than a bag of crisps is capable of making this 6,000 mile journey twice a year – travelling at an impressive 35mph, covering on average 200 miles per day.
Certainly, before the first swallow that had been ringed in Britain was found in the Natal in 1912, people had conjured up all sorts of theories to explain why some birds disappeared in winter.
The Ancients Greeks thought they hibernated in trees during the cold months while the idea that swallows hunkered down underneath the mud of riverbanks for the winter was taken seriously for centuries. Folk living in the Middle Ages even thought barnacle geese turned into barnacles.

Go north
But just why do birds undertake these journeys?
You may be surprised to know that many of the birds we claim as British probably originate from the African region. The nearer the Equator you get, the warmer the climate is and the more bountiful the food supply. However, this ideal setting attracts many species and competition for space and sustenance is fierce.
For example, in Africa there are at least eight species of cuckoo and an incredible 30 species of swallow and martin. With this abundance, some species decide to look elsewhere for a space for themselves.
Over the eons, as the time to breed has arrived, birds have flown north, attracted by Europe’s wet and warm summers, which is good for generating insect swarms. Our long days at this time of year also means parent birds can feed their young for more hours each day.
So, despite the treacherous journey – and many birds do fail to reach their destination – migration actually makes survival easier.

Cuckoo, photographed by Edmund Fellowes

I’m still waiting to hear my first cuckoo around Sudbury and Cornard but was fortunate enough to see several in Thetford Forest recently. I was shown their secret location by an expert from the British Trust for Ornithology (BTO), who has been using the latest satellite technology to track this iconic bird of our spring.
The tracking device is attached like a backpack to the bird and has a small solar panel on it that powers the equipment, which sends back information on the location of the cuckoo as it moves around. We didn’t have time to watch Line of Duty in our house last month, as we were too busy looking out for updates on the progress of one cuckoo called PJ as he made his way up from the Congo, where our cuckoos spend the majority of the year.
On his travels, PJ paused for a few weeks in Sierra Leone in western Africa, as it stocked up on caterpillars and piled on the grams in preparation for the greatest obstacle on his journey – the Sahara Desert. I learnt that cuckoos cross this great infertile expanse of sand and rock in one go – a 50-hour non-stop flight at over a kilometre high.
I also found out that cuckoos from Suffolk tend to go via the Spanish coast on their return trip while those from northern England and Scotland take a route through Italy where survival rates are better. The tracking devices – which have given scientists wonderful insights into the habits of migrant birds – also transmit tragic news. They send back details of the temperature of the cuckoos wearing them and my guide told of scientists watching a bird’s body warmth tail off in real-time as it perished on its journey.
So, when you do hear that cuckoo or willow warbler or marvel at the swifts and swallows performing aerobatics over Sudbury in the months to come – ponder on the effort they have made to be here.
You would also be wise to enjoy them while you can because, like our all too brief summer, their stay is short and dramatic before they have to head home and go through their epic journeys all over again.

Ross Bentley, Trustee of the Sudbury Common Lands Charity