Flyway Highway

The more we learn about bird migration from satellite tracking and the night time recording of over-flying birds the more remarkable the story becomes; as if it wasn’t remarkable enough anyway!

Guy Belcher recorded 43 Whimbrels over Little Shelford on 20th August – they were likely Siberian birds moving south and they probably passed over our project area. The north westerly winds today (25th August) will probably produce a show of Arctic and Great Skuas (Bonxies) on the north Norfolk Coast. The curious thing about these birds is they appear to fly west and into the Wash rather than follow the coast east then south on their southerly migration. Observations suggest they exit the Wash at the mouths of the rivers that flow into it – the Great Ouse and the Nene – and continue a south-westerly overland migration following these river valleys. They continue south-west to join the Severn estuary and so “short-cut” the route round south-east England and arrive into the Atlantic much quicker.

The Whimbrels were possibly following the same track. A comparable spring migration has been observed with skuas following the Great Glen north-east from the Atlantic to the North Sea avoiding the route around the north of Scotland. I once saw an unseasonal immature Arctic Skua fly out of the mist in mid-January 1985 at a farm reservoir in our project area.

Whimbrel – wintering on Teneriffe October 2017

Skylark – Garth Peacock

Our project area could be a major flyway highway! In the 1960/1970’s Graham Easy observed Skuas over Milton but at a great height moving south west over the City. The trouble is that skuas usually fly too high to be seen and do not call so cannot be picked up by night-time sound recording (“noc-mig”). Migration height is another puzzle with some recent evidence that songbirds fly at altitudes of 5-6 km. This comes as no surprise. It was once assumed that Siberian migrants flew round the Himalayas to avoid flying at extreme altitude over the mountains and then filtered east and west to over-winter in the Indian sub-continent. In the 1970’s local birders camped in the Himalayas above the tree line noticed large early morning flocks of thrushes making land fall from the north. They had clearly come straight over nearby 6-7 km high Himalayan peaks.

It makes sense for the Whimbrels, Guy recorded, to follow the Ouse/Cam valley over our project area. Many winter in west Africa and on the Canary Islands and this is a much more direct route from Scandinavia than following the coast of England to the Atlantic. However, some do just that and I recently saw two groups of 10 and 15 flying south past Southwold.

Recent finds below the feeding perches of the City centre Peregrines include the severed head of a Moorhen and Black-tailed Godwit feathers! How the severed Moorhen’s head got there is anyone’s guess – an overhead migrant perhaps!? I don’t think I have ever seen a Moorhen fly any higher than 5 m! I suspect our City centre Peregrines hunt over the Ouse Wash. I have seen Peregrines heading north-east over Castle Hill/Huntingdon Road and between Girton and Impington and sitting in the aerial tower at Over. The general trajectory of travel seems to be towards the Washes and I have seen birds hunting at Chain Corner between Earith and Sutton Gault.

A recent article in The Observer (RSPB chief warns: we’ve got to protect our rare birds. 19.08.18) talks about the loss of 420 million birds in western Europe. The article specifically mentions Cirl Buntings which were occasionally recorded in our study area in the 1940’s and 1950’s (Bircham 1989). They are now only found in south Devon and Cornwall and were the subject of a successful RSPB recovery programme. Farmers there have combined to grow successions of spring crops leaving weedy over-winter stubbles on which the birds feed. Turtle Doves have declined by 90% which might be due, in part, to the loss of habitat in their African wintering grounds. This is the first year (in my birdwatching life-time) I have not seen a Turtle Dove.

The development at Darwin Green pushes our farmland birds: Skylarks, Yellow Wagtails, Yellowhammers, Linnets and Grey Partridges further to the edge of our project area whilst species like the Tree Sparrow have been lost. The devastation of adjacent landscapes and habitats due to the A14 widening might mean these species may require specific recovery programmes in the future like the Cirl Bunting.

Turtle Dove – Garth Peacock

Tree Sparrow

Watch for unexpected autumn migrants in back gardens. An easterly wind followed by rain could bring new birds to your local patch and garden. Two autumns ago, a mixed flock of tits included Willow Warblers, Chiffchaffs, a Lesser Whitethroat and a Reed Warbler in my very small Chesterton garden. Later in October, and if you are lucky, listen for the high pitched, rising “suwheet” call of Yellow-browed Warblers – they like Sycamores. Not to be confused with the contact calls of overflying Redwings, especially at night, that begin to arrive in numbers from the end of September – that’s a thin, high, flat “zeep”!

Bircham, P.M.M. (1985) The Birds of Cambridgeshire. Cambridge University Press.

Bob Jarman

27th August 2018