British Wildlife of the Week

Willow Tit

It wasn’t until the end of the 19th century, at the tail end of Queen Victoria’s reign, that the willow tit was detected here in the British Isles. Considering it is a native breeding bird that was reasonably common at the time, this may seem surprisingly late. But this apparent oversight becomes much clearer when you realise just how much the willow tit looks like one of its close relatives.

The willow tit is a small greyish-brown bird with a black cap and a black bib. The marsh tit is also a small greyish-brown bird with a black cap and a black bib. In the field, based on appearance alone, it is very difficult to reliably tell them apart with any real confidence. At least, that’s the case in the UK. The willow tit is distributed across most of temperate Europe and Asia, but identification isn’t so much of a problem in the east of its range because there it is much paler than the marsh tit, providing a relatively easy way of telling the two species apart. As you travel further west, however, the various races and subspecies of willow tit start to look more and more like the marsh tit, so by the time you reach the UK, the two species look virtually identical. And therein lies the confusion, because for centuries it was assumed that all members of both species living here were marsh tits. The willow tit was simply viewed as an unfamiliar foreign species.

Then, in 1897, it was discovered that there were, in fact, two small greyish-brown, black-capped tits in the country. Rather embarrassingly for the Brits, it was two German ornithologists who realised this. Otto Kleinschmidt and his colleague Ernst Hartert were examining a tray of skins at the British Museum when they discovered that a bird labelled ‘marsh tit’, which had been collected from the suburbs of north London, was actually a different species, one they were familiar with from back home: the willow tit. Finally, after being overlooked for so long, the willow tit was confirmed as a British breeding bird, becoming the last of our already-resident birds to be recognised [1]. It had been hiding here all along, in plain sight.

So how do you tell a willow tit and a marsh tit apart? If you’re going on appearance alone, the answer is ‘with extreme difficulty’, even if you’re an experienced birder with top-of-the-range optical equipment. But, if you must know, the willow tit has paler edges along some of its flight feathers and a slightly larger bib, whereas the marsh tit has a pale grey spot at the base of the upper mandible and a glossier black cap. However, these very slight differences, subtle enough to have remained unnoticed for so long, are rarely apparent in the field. It is much easier to tell them apart by their very distinctive songs. A willow tit has a call that has been transcribed as ‘zee-zurzur-zur’, while a marsh tit’s call has been likened, rather delightfully in my opinion, to a ‘discreet sneeze’.

Unfortunately (and yes, in case you hadn’t already realised, there’s almost always an unfortunately when it comes to animals), the willow tit is considered the UK’s most threatened resident bird. Numbers of this unique subspecies have plummeted by 94% since 1970, and by a third since 2008, likely due to a deterioration of quality woodlands and the loss of understorey vegetation. This is the largest decline of any UK resident bird and it is now extinct in most of its former haunts in the south and southeast of England.

Sadly, few people are aware of this bird’s precarious position. The willow tit has already been overlooked before. Hopefully, it won’t happen again.

In the next British Wildlife of the Week, we’ll be looking at an aquatic arachnid, the only spider in the world that lives almost entirely underwater – the aptly-named water spider.

^{_{[1] At least, until the separation of the common crossbill and the Scottish crossbill – but that’s a story for another time.}}