As I crossed campus yesterday in the heat of the afternoon, I felt a gentle tickling sensation on my forearm. A winged ant, crawling and questing as ants do, before finally recalling that – O happiest and most fortunate of ants! – it could fly, and launched itself back into the thundery air. Memory jogged, I recalled seeing a mass ant emergence and subsequent feeding frenzy of gulls in Bristol mentioned on Twitter that morning. I looked up expectantly – you don’t have much luck as a birder if you go around staring sullenly at the ground – and there was the same scene, being played out in the skies above Reading.
We’re never a town to be outdone in the urban wildlife spectacle stakes, you see. And spectacle is the word as 50, 60, 70, maybe more than 100 gulls, mostly lithe, silvery-white black-headed gulls with a few lesser black-backed gulls mixed in for good measure, looped and swooped and tied knots all through the urban airspace north of Whiteknights. The more I looked across the sky, the more gulls I could see, spiralling up in broad columns towards the clouds.
I wondered after a while if I might be able to capture the scene on film and dashed inside for my camera. Since parts of the Harborne Building are air-conditioned, the lure of cooling off became overwhelming, and I lingered for ten minutes or so. In that short time the first swarm must have dissipated, for just a few gulls in twos and threes were still popping in and out of view above the treeline by the time I re-emerged. So I amused myself in the way I had originally intended to, by dropping in on my friends the burdock gall flies and paying respects to a new friend, a rather tastefully attired weevil named Malvapion malvae that feeds on common mallow (which is currently flowering rather beautifully in a number of places around campus).
About half an hour later I was still poking at flowers, drawing the usual dubious glances from passersby, when I heard the familiar jagged scream of a black-headed gull, and saw a few birds begin to gather and circle, this time directly overhead. Groups of gulls winged purposefully from all points of the compass to join them, calling out the good news to each other via a particularly rasping cry somewhat reminiscent of their usual alarm call. A few enterprising individuals had clearly located a decent ant patch and were drawing others in with audio-visual signals, their screeches and swoops a kind of dinner gong.
This is where I confess to having done no research at all for this post*, so please look up the facts for yourself, but my reckoning is that warm, humid weather signals to winged ants waiting underground (if that seems plausible?) that conditions are right for dispersal, and following that cue they emerge en masse, from nest after nest, seeking to take advantage of a convenient convective plume that will carry them up and away to pastures new. Concentrated in this way, each relatively lightweight ant becomes part of a nutritious whole, a rich aerial plankton that must be irresistible to any bird alert enough to spot them and manoeuvrable enough to scoop them out of the sky.
Gulls are excellent opportunists, yet still I find their ability to spot and congregate around ant swarms in this way mighty impressive. I’d love to know more about how the feeding flocks form and reform, and it would be even more interesting, as a one-time meteorologist, to know how closely the great whorls of feeding birds map on to rising, twisting columns of convective air. Do black-headed gulls on ant-days behave almost like those daft little sensors in Twister, making visible the otherwise unseen (clouds aside) motions of the atmosphere? I suppose it depends on how powerful the ants’ own flight is, on the interplay between upper-level winds and the relatively feeble beat of their flimsy wings, and how doggedly the gulls manage to stick with them. What a beautiful, mysterious, complex world we live in.
*Update – Flying Ant Survey! (https://www.societyofbiology.org/get-involved/biologyweek/flying-ant-survey) This may provide some answers, and the folks behind it are looking to gather more data. So those of us who’ve seen flying ants recently should submit our sightings! Who could refuse to help a project with such a good logo?