Marsh tits and willow tits: A major ID challenge
Bob Jarman discusses the two most difficult birds to identify -- and admits he was wrong!
I once gave a short talk to the Cambridgeshire Bird Club called “I don’t believe it!”
It was about the marsh tit and the willow tit, the UK’s two most difficult birds to identify and separate. I claimed they were indistinguishable, and the same species. At the end of the talk there was polite silence, no questions and the meeting moved quickly on to the next short talk. I was wrong!
Richard Broughton, a local research ornithologist, has just written a ground-breaking book that puts me right and in which he describes the differences between these two species.
“I had willow tits on my local patch in Hull when I was a youngster at school,” said Richard “and I had marsh tits and willow tits around my first office near Huntingdon when I started my science career. They’re a lot like us, mostly preferring to live as couples in stable relationships, with busy social lives and a close attachment to their neighbourhood.”
Despite its name, the marsh tit is a bird of mature established woodlands. It used to be regular in the woods around Madingley and I see just a single pair now in Gamlingay Wood on my annual bird surveys for the Wildlife Trust.
The willow tit is now extinct as a breeding bird in Cambridgeshire and last bred at Wicken Fen in the early 1990s. It is now a bird of marginal secondary habitats, often surrounding wetlands. Its numbers have fallen sharply since the 1970s, and it has seen a 96 per cent decline between 1967 and 2022. I have seen it in mainland Europe as a bird of pine forests.
There are now 37 per cent fewer woodland birds since 1970 and the marsh tit has also declined in that period by 80 per cent.
“These birds are telling us that something serious is happening in the woods,” said Richard. “We don’t fully understand exactly why they’re declining in many areas, so the inspiration for writing the book was partly to bring together all that we know about their identification and ecology and what pressures they’re facing. If marsh tits and willow tits are struggling then we need to listen to what this is telling us about our woodlands and forests,” said Richard.
“There is growing evidence that increasing numbers of blue tits and great tits could be harming marsh tits and willow tits by taking over their nests and dominating their foraging space” said Richard. “The vast scale of bird-feeding in gardens, woodlands and nature reserves is changing our woodland bird communities and it really boosts the dominant species, which can then put extra pressure on marsh tits and willow tits. For this reason, it’s important to consider the unintended negative impacts of well-meaning interventions, such as bird-feeding and nestboxes, on more vulnerable species like these.“
Although superficially so similar, the two species actually have very different nesting habits. “Marsh tits use existing holes in trees but willow tits excavate their own nest hole. They both have very large territories and you could fit 15 pairs of blue tits into a typical marsh tit or willow tit territory.
“These large areas contain enough natural nest sites for marsh tits and willow tits, and so these species are limited by the area of woodland habitat and not by the availability of tree cavities or deadwood for building their nests. Adding nest boxes cannot increase the numbers of marsh tits or willow tits like it does for blue tits,” said Richard.
The single biggest cause of nest failure is predation, and the main predator of marsh and willow tits nests is the great spotted woodpecker. Numbers of this woodpecker have increased in the last few years.
“I’m still monitoring my marsh tit population at Monks Wood in Cambridgeshire, coming up to 24 years of study,” said Richard. “When I started the study there were 22 pairs in this wood. Last year there were fewer than 10.”