The last time Shearwater's Jonathan Meiburg was in London, it was on an bird research expedition, part of which was documented on these very pages. His current visit here, on Shearwater's European tour, is much less avian-focused, though as the old saying goes: you can't keep a good ornithologist down.

"We just took the ferry over today, we were playing in Lille last night," Meiburg tells me in the band's dressing room deep in the bowels of London's Islington Assembly Hall, the evening before their headline show. "Great day to be on the water - we saw some gannets flying around. There were actually some shearwaters too!"

This is more or less how Meiburg introduces himself and, given that it's next to impossible to read anything on Shearwater without Meiburg's other passion being mentioned, it's genuinely wonderful that it's impossible to speak to the man himself without it coming up either. He has managed, so far, to balance his interests in academia and music, often combining the two, with songs and albums frequently themed around winged life and the natural world.

Jet Plane and Oxbow, the band's latest album and second for Sub Pop, is the farthest they've ever gotten away from that natural world, their most synthetic, synthesised effort to date. After the band's epic, orchestral 'Island Arc' trilogy of Palo Santo, Rook and The Golden Archipelago and 2012's relatively minimalist Animal Joy, Jet Plane and Oxbow expands the band's sonic aesthetic while remaining defiantly Shearwater. (Unsurprising, given that the band's real defining feature is Meiburg's vocals and the man himself: "I'm the only one who can't quit," he jokes.)

"It's sort of more personal than [the Island Arc]," he explains. "Which bothered me a little bit at the time. I didn't mean to do that, but then when I went back and listened to them it felt like that. So when I was working on Animal Joy, at the top of the lyrics document - I always make a really big document with all the lyrics on it - it said 'write like a human being.' And that's what I've been trying to do since."

While I don't quite accept that the Island Arc records lack humanity, it's clear that Meiburg has moved toward a different type of songwriting, incorporating some more traditional rock tropes (things like, you know, choruses and hooks) and a more direct, first-person experiential approach to lyrics.

"You can only get so engaged in that kind of God's eye-view of the world," he says. "Although the new record has some of that too, but it's measured. I think it scales all the way from very small and close up to very wide.

"The first decisions that you make in any creative project are the most important. They're the ones that really set the course for the whole thing, and then you can at least try to aim at something specific. And you might not hit it, but at least it going to be different from where you were heading before."

While Meiburg says Jet Plane and Oxbow didn't have any "write like a human"-style mantra, that "first decision" was prompted, as are so many things, by David Bowie.

"I heard a quote from an interview that David Bowie made for Scary Monsters, and he said that he considered it social protest music. And I thought, Scary Monsters is social protest music?!" he recalls. "And then I went back and listened to it again and you know, it really kind of is. And I thought it felt like the right time for me personally and also just the time that we're in, that it was time to make a protest record that wasn't dumb, or preachy, or in your face exactly, but nevertheless was a way of look at the world. All the records I really love there's room for you in the records. If it's just somebody yelling at you then it's like 'aah, go away!', unless somehow that person yelling stands in for you. Animal Joy was very much about my life specifically, but I wanted this one to be just as personal but more about a life in context, in the context of political forces roiling in the United States and the pathologies that we just seem so unable rid ourselves of year after year after year.

"Even the idea of 'protest music' sometimes makes people run. But protest is a valid thing for music to be. A protest is just a form of engagement with the world that you're in. It's what art is supposed to do. Just saying 'no' to things is still quite powerful. 'I don't believe in this. This is not it.' Even if you don't know what the right way is, it's okay to say 'it's not this'!"

While Shearwater have succeeded in not being dumb, or preachy, or in your face, there are moments on the record where that social protest element will come into stark relief. There are two songs on the record which have 'America' in the title; there are at least two which mention guns in the lyrics. And yet Jet Plane works like it does because of its essential ambiguity, precisely because it is not preaching but asking questions, not yelling at you but probing, examining, exploring. (It's worth noting, by the by, that in the liner notes for Shearwater's covers LP Fellow Travelers, Meiburg quotes Leon Trotsky: 'A protest against reality, either conscious or unconscious, active or passive, optimistic or pessimistic, always forms part of a really creative piece of work.' It's fair to say that Meiburg follows Trotsky in his belief that all art is protest, and that's probably the best way to think of Jet Plane as a 'protest' album.)

"That was the whole point of the record," Meiburg says. "I wanted to make a record about the United States, about what it means to live there and what's beautiful and frustrating about it.

"Within the US we have strains of things that affect people all over the place but because we're 'big and powerful', our bad actions are bigger, but probably our good actions are bigger as well. Everything's just bigger. People have to pay attention to it because they're forced to. And every place really breeds its own kinds of special varieties of good and evil. For us there's the militarism and the knee-jerk nationalism, the mercilessness, the dark-side of America's vaunted rugged individualism. I just can't believe how much hatred there is within the country sometimes of people who are poor, or struggling, or desperate - and at the same time worship of that story! It's really weird."

At least, I respond, the American side has that worship, the 'American dream' rags-to-riches mythology that, however misguidedly, informs so much of the country's identity. A modern protest album from the British perspective in 2016, surveying our current political landscape, is surely all about keeping the little guy down.

"Right! There's no possible good ending to this story!" he laughs. "I noticed that about the British and American versions of the Office. The British version is all about everyone expects to be miserable, and that's where the humour comes from. The American version is, everyone expects to be happy, and that's where the humour comes from. People might go through some downtimes but they're going to succeed in the end - can you imagine that in the UK, that would just not fly here. Like Saxondale, I cannot imagine a single episode of that playing in the US at all! They'd just be like 'why is this funny, this poor guy. Nothing good ever happens to him.'"

Meiburg, of course, encountered Steve Coogan's Saxondale while on tour in the UK, and it's exactly the minutiae of this kind of cultural cross-pollination, the spectrum of life experienced while traveling the world that has long made touring musicians uniquely placed to write art about 'home', wherever that might be.

"There's that sense you have, you know, when you go away from home as you do in this job, for longish periods of time, and then you come back to it and suddenly home seems unfamiliar," he says. "For a few days, sometimes, and then it takes a little while to settle back out. At first you feel like there's something wrong with you, like all those things that are familiar just aren't quite themselves.

"I like traveling. Its been a big part of my life ever since I was just out of university I guess. I never thought exactly that it would be, but as a child I spent a lot of time look at the globe, running my hands over it. I remember the way that China, that the Himalayas felt on the globe. It feels like it's this great big secret because somehow that's you, that's a picture of you somehow, but from very far away."

I'm reminded of what Meiburg said earlier, about writing like a human, about not taking a God's eye view of the world. If the Island Arc is Meiburg running his fingers over the globe, imagining the great big secrets of distant lives in faraway lands, Jet Plane could only have been written by someone who had reconciled the distance of that picture.

"I guess so," he says. "I guess that is what's so liberating about touring - as far as your own personal space, where you feel like you are, it shrinks down to about the size of your body and your bag. Which is mostly liberating. Exhausting, but liberating. I'm about to turn 40 and I'm still backpacking!

"And then you just make your own little homes from home. The van is a constant. We joke about how people tend to carve out a place in the van and then it can be very difficult to drag them out of it! So that becomes a constant; the people are a constant; and the stage set-up every night is very comfortingly consistent. You set up your own little imaginary world, the lights that we've got that you'll see in the show tonight, it gives a continuity to it."

Jet Plane and Oxbow leans on a whole litany of inspirations, from the standard Shearwater touch points (Talk Talk, early R.E.M.) to a range of new influences, the likes of mid-80s U2 and, as reflected in the two-cover encore, Berlin Trilogy Bowie. The live show, however, resembles nothing so much as a budget Radiohead for the austerity era. The lights Meiburg mentions, the band had shipped out to them from Glasgow for the first date of this tour in Berlin; they illuminate the stage in bright primary colours, reflecting the album's artwork. Reworked and retooled slightly for the live environment, some new tracks, 'Prime' and 'Filaments' particularly, a reminiscent of the back-to-basics approach of In Rainbows, if Thom Yorke could really, really sing. (And yeah, Thom Yorke can sing, but he sings like we all think we could sing; Meiburg sings like a classically trained angel.)

The tour has been, Meiburg says, "exhausting, like tours always are." This European tour will see Shearwater play 18 shows in 19 days in eight different countries.

"But we've had bigger audiences and better shows than we've had maybe ever," he goes on. "It's been really exciting. The show is more extroverted than its ever been too. You have to have an audience that allows you to do that, is the thing. And the audience is finally actually turning up!"

Meiburg says that the 'terrifying' experience of opening for Coldplay in 2008 - back when Shearwater only really had two full-length albums under their belts - was a crucial step on the learning curve of how to play to bigger audiences.

"You step out there and it's like, 'Oh my God, I can't believe...'" he says. "There's 20,000 people and... they're not there to see you. So you play for your 30 minutes and run away. Now I do a much better job of it. We're appreciating the different things you can do in a larger venue, especially with a better and more powerful PA. You're so hamstrung by PAs in smaller rooms a lot of the time, especially if you're trying to make big sounding music, which we do. It's a little scary, I'm just trying to learn how to do it because I haven't done it like this before."

The Radiohead comparison holds up in more than just aesthetic. Shearwater's live performance is intense, muscular; for all that Meiburg is an unassuming, bookish type, he is a genuine presence on stage, investing a song like 'The Snow Leopard' - which I have previously never been overly fond of - with a burning energy, culminating in a Swan Lake-esque transformation when he sprouts laser wings and seems, for a moment, to envelop the entire venue. Shearwater have always, in their way, been a rock band, but first with Animal Joy and now with Jet Plane, they have emerged fully as a Rock band.

A few years ago, to finally put a full-stop on the Island Arc era, Shearwater played the entire trilogy to a sold-out show in Austin, Texas. A little later, having been unable to attend, I recreated the performance in my own way, staying up one night when working on my master's degree, listening to all three records back-to-back.

"Glad I could help!" he laughs. "Actually, this is the thing that's really cool about having hung in for this long. You start to hear stories like this, like how this thing you made somehow, five or ten years later, ended up in the hands of someone to whom it meant something. And it's just more gratifying than any other part of it. It makes you feel like you did have some real value whether it made any money or not. Something Jamie [Stewart, of Xiu Xiu, with whom Meiburg collaborated on one self-titled album as Blue Water White Death] said to me was that if you make something really extreme - and Jamie has made some really extreme stuff - that there will be an audience for it. Not necessarily very big, but it's out there, if you reach for it, if you really go for it, there will be people who like what you're doing."

Shearwater's latest album, Jet Plane and Oxbow, is out now on Sub Pop.