The Return of Summer Migrants

In spite of the extraordinary lack of rain the grass is now beginning to grow and the cattle are returning to the riverside following a tradition of centuries. Originally the cattle would have been left to their own devices but nowadays the Sudbury Commons are thronged with people and dogs and those dog owners have a responsibility to keep pets under close control. Each year there are more people and it seems, inevitably, there are more entirely avoidable and unnecessary incidents. Please exercise care and consideration when out on the riverside. Please keep away from all livestock and allow the cattle to settle down for the new season unhindered and undisturbed.

From March through to May we witness the return of our summer migrants. It may be a new snatch of song heralding the return of the chiffchaff, blackcap, sedge, reed or willow warbler or even the fast declining cuckoo. It could be the sight of the first swallow quickly followed by the house martin and then the swift. All these herald the coming of summer even if the weather is inclined to feel rather at odds with our idea of summer.

The riverside is a hugely important resource for swallows, house martins and the larger swifts. Through the long summer days these birds ‘work’ the air above the meadows. Although superficially similar the swift is of a more ancient evolutionary origin than either the swallow or the martin which are related to one another. Swifts graced the skies when dinosaurs tramped the earth while swallows and martins evolved a mere fifty millions years ago! Swifts are apparently, and perhaps rather astonishingly, more closely related to hummingbirds and owls.

All three species provide a constant source of pleasure for those who appreciate our wildlife. Sadly all are declining rapidly although sometimes it would seem otherwise over the rich riverside oasis where these birds can been seen. The reason for this is simple; the air is filled with the insects they need to sustain them and their broods. On traditionally managed farmland such as the riverside pastures millions of insect larvae live in the soil breaking down the organic material or a summer’s worth of cow dung or live the larval stages of their lives in the numerous ditches and ponds. When these emerge as adults to feed and breed they contribute to the ‘aero-plankton’ above the pastures which attracts these birds from a considerable distance. Meanwhile the vast open acres of intensively managed farmland have little to offer them and thus these birds will continue to decline.

The supremely fast and agile swallows tend to skim low over the pastures and ditches while martins and swifts fly considerably higher. They are all feeding on insects but unseasonal weather with a cold and wet period during the summer will seriously affect their breeding success. House martins, in particular, have a relatively short life averaging just three years. Warm summers, therefore, are necessary for the survival of the species. The issue is that there are simply no longer enough suitable habitats to generate their insect food and thus bird numbers have been collapsing catastrophically since the 1960s.