Spring gathering

The April weather has been glorious and the Wharfedale naturalists have been making the most of it. On a walk by the Wharfe, I was delighted to see that sand martins, generally the earliest members of the hirundine family to arrive, here in good numbers, wheeling and darting over their nest site behind the Ilkley Tennis Club. Usually house martins and swallows arrive next, and swifts, those aerial speed-merchants, rather later, but two fellow-naturalists are pretty sure they caught a tantalisingly brief glimpse of a swift flying high above Littondale as early as the 11th of April!

Another WNS couple had an even more amazing experience. They were walking along a track near Rylstone when they became aware of a clamorous noise which increased in volume as they walked on. "Rather like the chattering of starlings coming to roost, but with a deeper undertone and overlaid with squawks and caws." They identified the noise - now deafening - as coming from a steep gill, wooded with conifers. As they examined this through binoculars, they realised that the wood was full of birds, just two or three to a tree, but, they estimated, at least fifty in all. Every so often a single bird would emerge, do a short flight round and return, and this gave them a chance for identification. The birds were jays. Our friends had come across the mysterious phenomenon known as a Spring Gathering, an event rarely observed and only described in detail in a few specialist ornithology books.

Jays are members of the crow family, all of which have a complex and fascinating social life and a rich language of vocal signs to support it. Unlike rooks and jackdaws, however, jays are relatively solitary birds - I've considered myself lucky to see two or three at a time. However, they occasionally congregate in considerable numbers for a brief time - sometimes as little as twenty minutes - and behave in just the way our friends observed. The purpose of these gatherings is obscure. Jays mate for life, but some experts think the gathering is related to pairing - perhaps reinforcing pair bonds and enabling singletons to find a mate in a sort of avian version of speed dating. Whatever the explanation, our friends had clearly been very lucky to see, and hear, such a rare event, though as so often in nature, you're left with as many questions as answers. This is clearly a hugely exciting experience for the participants. Jays are thinly dispersed across the countryside, so such a large number must have been drawn in from a wide area. But, how do they know where and when to come for this thrilling event? And they have to be punctual - it could all be over in twenty minutes!

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