If you’ve recently heard honking noises overhead, with luck you’ll have spotted huge echelons of geese making their way north for the summer. Over the past month I’ve seen them from Cumbria and Perth & Kinross.
During autumn and early winter, more than half a million geese fly to our shores from frozen areas further north. The main migratory species are pink-footed, barnacle and brent geese and, even if they are just specks in the sky, there’s a fair chance you can guess what you’ve just seen from your location and their direction and pattern of flight.
Pink-footed geese are the most common and tend to congregate along the east coast and in northwest and central England, while barnacle geese mainly spend winter in the western Isles of Scotland and the Solway Firth. Pink-footed geese usually fly in orderly V-shaped patterns, using the uplift from vortices shed by the wings of the bird in front to reduce the effort required, while barnacle geese achieve the same effect by flying in a staggered line astern. Like Tour de France riders, some take it in turns to go out in front to share the effort.
In contrast, brent geese fly in more ragged formations, with the dark-bellied type making its annual commute between Siberia and south and east England, and the light-bellied type travelling from Canada and Greenland to Northern Ireland. Some also spend winter around Lindisfarne in northeast England.
A ragged skein of light-bellied brent geese seen a few days ago near Perth, possibly on route from Lindisfarne to Greenland or Canada
As with all bird migrations, it’s fascinating to think about how they navigate and after a little thought you can often see problems with any theory that’s proposed. For example, maybe they follow line features on the ground such as coastlines and mountain ranges, or fly IFR (see later), but what happens if it’s foggy and how do some species navigate at night and across oceans?
One long-standing theory is that they use the stars as in the early days of airline flight or the light of a full moon, but what if there is high cloud or bad weather on route? Or perhaps adult birds guide their offspring on the first few trips, but what about the Lake District’s ospreys, whose chicks only head down to west Africa about three weeks after the adults depart? Other long-established ideas are that birds detect miniscule changes in the ‘smell’ of the atmosphere, or detect variations in the earth’s magnetic field via magnetite particles in their beaks.
Perhaps the most intriguing theory of all is that some species can visualize variations in the direction and inclination of the magnetic field. Called visual magnetoreception, this idea arises from the world of quantum physics and holds that certain molecules in a bird’s retina generate photochemicals that appear as a shadow overlain on the landscape, a bit like a head up display on an airliner or fighter jet. It’s purely speculation but this may appear as a darker area whose position, size and intensity vary with magnetic conditions.
I first heard of this idea several years ago when chatting with a ranger at the WWT Caerlaverock nature reserve near Dumfries about a documentary that had just been filmed there. This was on research on magnetoreception in European robins by the University of Oxford, I think, who have since gone on to demonstrate some of these theories in practice using laboratory grown material.
Of course, Northern Lights enthusiasts may wonder what happens during a geomagnetic storm and recent research by the University of Michigan suggests that some species do indeed delay their departure if a storm is taking place or are more likely to take a wrong turn if one occurs once underway. Longer term changes in the earth’s magnetic field may also be a factor, which will be familiar to any hillwalker or pilot who has grappled with the differences between true and magnetic north.
Overall, though, this sixth sense sounds possible and its molecular basis makes inheriting route information seem more plausible too; ecologists talk about adults passing on key compass headings and magnetic signposts such as changes in inclination. However, as with most good theories it’s not the whole answer and in practice birds probably use a range of approaches, refining them on each trip to improve their navigational accuracy.
For nature-watchers, in addition to their annual migrations some geese species have another treat in store, namely the dawn flights they make inland to feed on grass, seeds and roots and the return flights in the evening to seek safety offshore.
The barnacle geese of the Solway Firth are a good example and more than 40,000 of this photogenic black and white goose arrive in some years. Most are from the Svalbard archipelago in Norway and GPS-tracking has shown that their favoured route is to make landfall on the main Norwegian landmass, follow the coast southwards and then head across the North Sea and Scotland to the Solway Firth. Cruise speeds in flight are about 30-40 mph for the two thousand mile journey at heights of a few hundred feet.
Barnacle geese at RSPB Mersehead
Some of the largest numbers settle in three nature reserves near the mouth of the Nith Estuary, namely WWT’s and NatureScot’s Caerlaverock reserves to the east and the RSPB’s Mersehead reserve to the west.
Several years ago I went on a guided goose-spotting walk at WWT Caerlaverock with the evocative name ‘Dawn Flight’, seeing huge processions of geese but missing out on the iconic sight of them silhouetted against the rising sun, it being cloudy that day.
Today seemed a good time to visit again but later in the morning this time. The most remote hide is a beautiful wild spot with saltmarsh stretching off into the distance against a backdrop of Lake District hills.
At this time of year the geese spend much of their time on the saltmarsh, being almost fully fuelled for the flight north. One person said that all it will take is a following wind and a full moon for them to depart. In the meantime they put on an impressive display with several large flocks flying along the shoreline as the tide moved in, a spectacular sight to see.
Soon they’ll be on their way and not back until autumn, with a new batch of fledglings making their first trip south.
** The regulations governing most airline flights are called Instrument Flight Rules, IFR, which are sometimes jokingly referred to as ‘I Follow Roads’. Indeed, on one memorable cloud-free flight from Manchester, the pilot did seem to be following the M6 south before turning off at the M42 (although in reality was just following airways).
A Northern Lights postscript. If you read my post and comments on the Northern Lights last month, you’ll know that the year so far had been a lean time for sightings but that ironically there was an event within hours of making that post! Cloud defeated me that time but last Sunday saw the strongest geomagnetic storm in seven years, enough to affect radio and satellite communications. However, the magnetic field wasn’t suitably aligned for a good display and there were just a few sightings of a faint green arc further north. Surprisingly though due to a coronal hole and solar flares the previous night turned out to be much more impressive, with sightings down to Norfolk and Northern Ireland, with a green arc clearly visible to the eye and some impressive pink-purple rays on camera. Not sure what if any conclusions to draw from this other than that my title for that post ‘The elusive Northern Lights’ was spot on and that as with all natural spectacles if at first you don’t succeed … !
We have large populations of barnacle geese in NW Sutherland which we count for surveys. Wonderful birds.