Designing Better Bird Nesting Boxes with 3D-Printed Mycelium

Deep in the grounds of a stately palace near Oxford, in the southwest of England, designer Dan Parker is perched on a ladder, struggling to tie an unusual object to an ash tree. With his arms stretched high, Parker clings to something about the size of an electric toaster, with a rippled perimeter that looks like wood carved into waves.

The object is light and hollow, with a single circular hole on one side. But it is the outer surface that stands out most: a wall that's lumpy like cotton wool, yet hard, and, perhaps most notably, distinctly mushroom smelling.

"This is reishi," a type of oyster mushroom that grows in this part of England, says Parker, a researcher at the University of Melbourne. Over the past fortnight, he 3D-printed the basic box shape, using sawdust and plant-based biodegradable plastic, before cultivating fungus to gradually grow over the sides. This method of producing objects from the sturdy root-like mycelium of mushrooms has been employed in architecture to make everything from chairs to bricks, "because it grows relatively fast [and] strongly," Parker explains.

He calls the strange object a “prosthetic hollow” and its purpose becomes clear as he ascends the ladder again, this time to tie up a conventional bird nesting box with a sloping green roof. Parker's creation is intended to outdo the typical bird box, which is used all around the world, but often fails to attract target species—or worse, confines them to cold, leaky conditions that can kill chicks. By redesigning the nesting shelter from scratch, he aims to provide a better start to life for cavity-nesting songbirds such as the rare marsh tit.

Parker's experiment will compare 10 of these new shelters against 10 conventional boxes, testing if they can provide a more attractive home for marsh tits—a species that is on the decline in Great Britain—that is also measurably more effective at supporting the bird’s eggs to grow and fledge.

Parker is part of a team at the University of Melbourne's Deep Design Lab that scrutinizes bird boxes with an intensity that other designers apply to jet engines or skyscrapers. Near their home at Melbourne School of Design in Australia, the team first used 3D scanners to map the naturally occurring tree hollows where endangered powerful owls typically live. As hollowed-out old trees were disappearing, they employed a selection of tools, from VR goggles to generative algorithms, to build nesting structures that closely matched the owls’ needs.

In Blenheim Palace, an UNESCO World Heritage Site ringed by about 12,000 acres of forest and gardens, the team is putting the same approach to the test in service of some elusive birds. Since the 1970s, marsh tits' population in particular has halved, at a time when the birds' natural habitat—ancient trees rutted with hollows and cavities—have vanished from the landscape, largely due to agricultural intensification. Other once common songbirds, such as coal tits, sparrows, flycatcher, and nuthatches, have also been in decline. Yet nest boxes erected to support them have had barely any luck attracting inhabitants.

On this windy day in February, Parker has brought the full range of bird boxes to Blenheim Palace to demonstrate how generic ones often fail. At the bottom end is the cheap "Amazon knockoff," he says. The first thing you can see is its weakness, explains Joanna Bagniewska, a zoologist at Oxford University's graduate center, who will be monitoring the success of Parker's experiment over the course of two summers. "The wood is connected in a very flimsy way, so it will warp, and it will essentially fall apart," she says.

Field research has shown that nest boxes' temperatures fluctuate much more widely than natural hollows. Those with thin wood and gaps let in cold air and rain—often enough to kill juveniles. At worst, studies indicate nest boxes can act as ecological traps that lure birds to substandard homes that end up killing their inhabitants.

Parker's experiment is employing a widely used box certified by the Royal Society for the Protection of Birds conservation charity as its control. Although more durably designed, many conventional solutions favor aggressive generalists like the common great tits, which can easily out-muscle smaller birds like the marsh tit and blue tit. "I have seen blue tit carcasses incorporated into the nest lining when a great tit—which is bigger and bolder—has won the competition of the nesting site," says Ada Grabowska-Zhang, an ecologist at the University of Oxford.

In previous research conducted on nature reserves, only one percent of typical boxes were occupied by marsh tits, demonstrating the need for a tailored solution. Andrew Cleaves, founder of Birds on the Brink—the charity that is funding Parker's experiment—says that marsh tits sometimes avoid competition by inhabiting dormouse boxes, which have small entry holes near the trunk that great tits can’t enter. By integrating this preference in the design of boxes, conservationists improved the inhabitation rate to around nine percent.

The Deep Design Lab conceives each of their projects as "design experiments" that incorporate best practices from discoveries like these while testing new variables. "What we need to be doing is using the best of available scientific [and] engineering expertise to create those things, but also constantly collecting feedback," says Stanislav Roudavski, an architect and founder of the Deep Design Lab. If target species are avoiding boxes, perhaps for reasons we don't fully understand, we can learn to design better shelters by noting how they interact with prototypes like Parker's.

Martyn Stenning, an ecologist at the University of Sussex who has been using nest boxes since the 1980s, says the most important thing is to make sure boxes are guided by species' behavior in their natural habitat. Some pioneers have already made attempts to perfect the nesting box by integrating insights from birds' interactions with their habitats. Among the most important conclusions they’ve made are the need for effective predator proofing around the entry hole and avoiding the buildup of parasitic organisms in nest boxes.

Parker says his 3D-printed wood shell is designed to have the strength to stop predatory weasels, woodpeckers, and rats from gnawing their way in; the interior is also shaped like the rounded hollows that form inside a tree, reducing the number of right-angled joints and gaps where parasitic bugs can hide. But at Blenheim, the team's chief interest is testing mycelium as a building material—the first time it has been trialed at scale, says Parker.

In a previous study, the Deep Design Lab assessed the impact of mycelium over a 50 year lifespan against other material like plastic, which has been proposed as the main material for 300 million boxes to be built on utility poles in the United States. Compared to plastic, mycelium would cost 15 percent more but could reduce carbon emissions, energy consumption, and waste by more than 75 percent.

But most critically, "It’s got really good insulating properties", Parker says.

The first three weeks of a marsh tit's life, when it's in the nest, are a critical time to grow, says Grabowska-Zhang. "We want a nice fat chick," she says. If they're expending energy keeping warm rather than growing, "then the feathers are going to be worse quality [and] they're going to be lighter than they need to be."

Over the coming breeding season, which starts as England warms and key foods like oak caterpillars appear in mid-April, Grabowska-Zhang and Bagniewska will monitor which birds prefer which shelter and how nest-makers get on. Using an endoscope camera mounted on a long stick to peek through the hole, they can observe the nests uninvasively. "So have they started nesting and then abandoned it or are they still going?” says Parker.

They will also monitor the humidity and temperature variations inside Parker's boxes and the control, as well as any signs they are failing nesters. "You can count how many unhatched eggs there are, you can count how many dead chicks are left over," says Grabowska-Zhang.

For the monitoring team, there are two big questions. First, from the bird's point of view—relying on sensory cues that we perhaps can't perceive—are Parker's shelters preferable? "Is there something that they see or smell or sense in it that makes them more likely to go in it?" says Grabowska-Zhang.

The second, which is all-important to conservation, is whether this is "an adaptive choice" that benefits the birds’ survival, she adds. "Are they going to do better, leave more descendants, and therefore, for conservation, is this going to be a better choice?"