The Sheep’s Head Peninsula was today’s destination for exploring by bike and van. A finger-like projection of carboniferous granite and sedimentary seams thrust into the atlantic, it is one of the many headlands making up Ireland’s rugged south-west coastline.
A superb route circumnavigates the area, which made for a very pleasant cycle ride; hedgerows passed in a blur of wildflowers and the peaceful air meant the song of Willow Warblers and piping of Common Sandpipers was crystal clear.
It was watching the aerobatic prowess of a handful of fairly familiar bird species that caught my attention for today’s 30 Days Wild blog, though.
As Dad and I arrived at Sheep’s Head Lighthouse – the blustery tip of the peninsula – a stream of Great Black-backed Gulls appeared around the corner. A pretty brisk north-east wind was gusting up the cliff face at over 30mph, and yet the gulls simply drifted by on frigid wings in the updraft.
Above: a short timelapse of the gusts of wind accelerating down the leeward side of the peninsula and fanning out to sea (c) Ben Porter
This lead my train of thought onto the aerodynamic considerations of bird flight, and some of the mechanisms responsible for this incredible ability. So for my penultimate #30DaysWild blog I thought I’d focus a little on avian flight…
The shape of a bird’s wing is a very important dictator of a bird’s flight dynamics. As such, a bird’s flight pattern and energetics is affected by two important considerations…aspect ratio and wing loading. Aspect ratio refers to the ratio of wing span to wing area, whereas wing loading is the ratio of a bird’s weight to its wing area. There are four broad classifications of wing shape based on these parameters: elliptical wings, high speed wings, high aspect ratio wings and soaring wings.
Soaring Wing Shape
Returning to the great black-backed gulls that drifted effortlessly by…most gull species possess rather long and broad wings, which are very similar in design to conventional soarers ike vultures. The broad wing is incredibly efficient at providing lift, with a spread ‘hand’ of fingertips helping to reduce wingtip vortices and reducing drag.
It was amazing to watch the drifting flock of greater black-backed gulls gain several hundred feet in a matter of seconds in the gusting updraft, with barely a flap of the wings!
High Aspect Ratio wings
Looking down from the cliff-top beside Sheep’s Head lighthouse, we could see a handful of Gannets feeding below. Possessing a strikingly different wing shape to the gulls gliding by, Gannets are amongst a host of seabirds with high aspect ratio wings, which are long and thin.
This shape is perfectly suited to low-speed gliding and dynamic soaring: where wind shear and differing layers of wind speeds above the ocean can be utilised effectively in an immensely efficient technique for navigating over vast distances. Albatross wings are very similar, but even possess a locking mechanism in the bone structure to resist the intense forces their wings are subjected to. Swifts are another species with long, thin wings that have a very high aspect ratio. The downside of this shape is a rather low manoeuvrability, and a medium wing loading (the ratio of weight to wing surface area is quite high).
As we walked up towards the car park, a cry from overhead trained out eyes onto a pair of Choughs dropping like stones from above. With wide, elliptical wings and spread fingertips, these aerial acrobats are highly manoeuvrable and dynamic masters of the sky.
Choughs are always a delight to watch in flight, and this pair dived in a series of stalling plunges; wings tucked tight to their sides as they dropped vertically, before stalling with a brief flare of the wings; this repeated several times and accompanied with what you’d hope to be cries of wild enjoyment!
Returning in the campervan along the peninsula’s bumpy north road, I became aware of a cohort of swallows whisking up insects in our wake along the vegetated country lane.
Another true master of the air, Swallows are endowed with anatomical adaptations similar to the previous species: they posses rather short and elliptical wings that allow for a highly manoeuvrable flight style. Turning and twisting with a flare of the tail and flick of the wing, they can respond in an instant to snatch up a rogue insect.
The compromise here is an inability to glide or soar, which means the constant flapping to maintain lift is highly demanding energetically. This is why species like swallows spend most of the day hunting protein-rich insects kicked up by sheep, cows, and also camper vans! It was brilliant watching several birds clinging to the lee of the van, swooping into the breeze to snatch an insect and use every feather to guide its extreme aerobatic prowess. what superb birds
High Speed Wings
This last category of wing shape wasn’t actually represented in the day’s selection of birds: these species have heavy wing loading (small wings on relatively heavy birds) and short, pointed wings. Their flight style tends to be one of rapid wing beats and very fast flight. Ducks are a classic example, with the UK’s fastest horizontal-flying bird actually being an Eider! The disadvantage is a very high energetic cost to the constant flapping to generate enough lift to stay airborne.
So next time you see a blue tit fluttering at your bird feeder, a sparrowhawk darting inches over a nearby hedgerow, or simply a familiar herring gull drifting mischievously above a harbour, have a think about how they are staying aloft, and the adaptations responsible for such an adept ability.