David Darrell-Lambert, Bird Brain UK, & GiGL treasurer
Most people don’t look to the sky over London for migrating birds. I never used to. Until, way back in the early 1990s, I was waiting at a bus stop on Tottenham High Road. I looked up and noticed a smoky, long line of wood pigeons. I counted over four hundred before my bus turned up. I was impressed but didn’t realise at the time that this was the tip of an iceberg in terms of bird migration.
Throughout my ornithological career, I have seen colossal migrations around the world. I have seen the skies of Israel filled with eagles and buzzards, and witnessed hundreds of migrating warblers moving like a plague of locusts through the bushes in Canada. Amazing stuff. But what about London?
London? Bird migration? Well it does happen. While working on various surveys across the capital, I have seen some migration and occasionally picked up large-scale action. On 30 August 1992, on the Lea Valley Reservoirs, I recorded over 400 common terns, 120 bar-tailed godwits, 80 black terns and 30 grey plover migrating through.
In recent years, I have been trying to focus on picking up this sort of migration across the capital to highlight our commuting avian friends as they move around the globe.
There are two ways I record migration. Firstly, what we call visible migration. This normally means standing in one location with a good view across the sky to count birds in flight. It always kicks off early in the day, so you have to be up with the lark and be prepared to stand around waiting for something to happen.
In early autumn, August and September, you are most like to get hirundines, swallows and martins, moving through. It can be a trickle or it can be a massive volume. From late September through to November, thrushes, finches and pigeons start to move.
On 14 October 2017, I visited the migration hotspot of Hampstead Heath. After three hours, nearly two and half thousand individuals and twenty different bird species had moved through; mainly wood pigeons (921) and chaffinches (531). The wood pigeons mostly came out of the roost early in the morning and then headed off west and south. The chaffinches trickled through all morning. The UK is currently experiencing an influx of hawfinches from the continent, possibly caused by various species of tree failing to generate enough food. I counted 42 hawfinches on this one morning.
These numbers aren’t peculiar to Hampstead Heath. In Greenwich Park, local ornithologist Joe Beale has recorded 12,000 migratory birds from over 20 species between 15th October and 18th November 2017. The bulk were 5,000 wood pigeon, 3,500 starlings and 1,800 redwings. Also recorded were at least 47 hawfinches which previously have only been recorded four times in Greenwich Park since 1960.
The far eastern side of London has an amazing track record for migratory wood pigeon. This year, near Rainham Marshes, local birder Ruth Barnes counted forty two thousand moving through in one morning. This is about ten thousand short of the record count for the London area in Swancombe Marshes. My best count was four and half thousand in half an hour. I had a meeting to go to, so I don’t know happened after I left.
The second method I use for recording migration is auditory and done at night. In the 1990s, I read various reports of people who placed microphones on skyscrapers in America and used the recordings to work out what species and how many flew over each night. So now, from a secure location on the east side of London I set up my microphone and digital recorder to run all night. In the following days, I scan through the sonogram (a graphical picture of the sound) listening for bird sounds. I mark these, identify them and enter them onto a spreadsheet. I am now a complete avian sonogram junkie.
I first started this a year ago and am still catching up with recordings I made in the autumn. Three hours of recordings, take me half an hour to check, so it can take an hour and a half to review a quiet night. Busy nights will take many hours, if not days, to review.
On 12 October 2017, I recorded 500 calls including 412 redwing and 91 song thrush calls. On 14 October 2017, I recorded 3,568 calls, including 2,104 redwing, 944 song thrush and 407 blackbird calls. Most interestingly, I recorded 12 robins, four meadow pipits and two hawfinches.
Does this mean am I recording 2,104 individual redwings? No, this is just the number of calls logged. Sometimes, you are can hear several redwings calling to each other at different distances. Other times, you can hear a single bird calling frequently, getting louder as it gets closer. But this does not help us understand the numbers involved.
Watching and listening to redwings migrating during the day, you get a whole range of different calls from each flock. One day in southwest London a few years ago, I observed just under two and half thousand migrating redwings in two hours. Most were in large flocks of over a hundred a time. Hardly any called. Whole flocks would go over and only one call would be heard, while from another flock, I heard not a sausage. On other occasions, single birds would call several times. So all I can currently do with the night time recordings, is note the number of calls heard.
On the 12 October 2017 recording, I noted both robins and meadow pipits calling in the middle of night. This is very odd as robins are generally silent migrants and meadow pipits are a day time migrant.
During the spring and early autumn, I have recorded various odd birds migrating from little grebes to moorhens to little ringed plovers to grey herons to curlews.
This gives you an idea of the range of species being recorded and some of the quantities involved. I am still learning and a lack of waterproof equipment restricts when I can record. Currently, I only know of one other individual, Peter Alfrey at Beddington, who is using this recording technique in London. So what else is going on out there, and what other secrets does London hold as birds migrate at night?
You can listen to some of David’s recordings, including his night time migration recordings on Xeno Canto.