Guano mining: Our deadly obsession with bird poo

Guano is poo. It’s a word we typically use for the excrement of bats and seabirds.

When there are lots of these animals living in a small area – whether it’s bats in caves or bird colonies on islands – they produce huge amounts of poo in one place.

People have then harvested this guano, but where they have, trouble has historically followed.

What is guano used for?

Guano is filled with nutrients such as nitrogen and phosphorous. This makes it a wonderful fertiliser for our crops. In fact, we’ve been using guano in agriculture for more than 1,500 years.

It was particularly treasured by the Inca Empire. This realm once stretched more than 4,000 kilometres from Ecuador to Chile, reaching from the Pacific Ocean across the Andes Mountains. Soil in parts of this vast territory was nutrient poor, but using bird guano as a fertiliser helped the empire to thrive, providing food security to more than eight million people.

This valuable resource was produced by enormous colonies of seabirds, including Peruvian pelicans, guanay cormorants and Peruvian boobies, that lived on western South America’s coasts and islands. Their poo was so important to the Inca people that anyone who disturbed the seabirds faced the death penalty. In fact, these may be some of the earliest conservation laws. 

The secret of guano’s fertilising power first spread to Europe in the mid-1500s, following Spain’s arrival and colonisation of South America. Guano’s popularity peaked in the nineteenth century – often called The Guano Age – and continued into the twentieth century. While extraction initially centred on Peru, it eventually spread, in particular to Namibia and several Pacific islands. Hundreds of thousands of tonnes of guano was shipped to the northern hemisphere.

But guano ended up at the centre of several conflicts.

Several countries, including Britain, shored up their guano supply by claiming land far from home. The Guano Islands Act, for example, is why the USA has so many territories in the Pacific today – the legislation was created to allow the annexation of uninhabited islands filled with guano. Peru, Chile, Bolivia and Spain went to war over guano-producing land, borders and taxes. 

Guano mining was strenuous manual work. Labourers were often enslaved people, convicts and those otherwise coerced into working the guano fields. Atrocious conditions sometimes led to deadly rebellions.

Bird poo also helped to fuel the First World War thanks to its use as an ingredient in gunpowder.

It was a lucrative trade to be in. Guano was a crucial part of Peru’s economy throughout the nineteenth and twentieth centuries.

This global commodity’s legacy lives on in the UK. One British company once made more than £100,000 per year trading guano, which is equivalent to around £8,000,000 today. The extravagant country house Tyntesfield, in Somerset, was built with the profits. 

How did historical guano mining affect birds?

At the peak of guano mining, estimates suggest that Peru’s coasts and islands were home to some 53 million seabirds.

It’s tricky to work out exact numbers for historical populations and how much they changed. As Dr Alex Bond, our Principal Curator of Birds, points out, we didn’t really start counting birds reliably until the 1950s. But we know that guano mining sent some seabird populations spiralling into decline. One estimate states that these same Peruvian seabird populations had dropped to a mere 4.2 million by 2011.

“Because seabirds are relatively long lived, they only have one or two eggs a year, generally, and so, if they skip a year breeding, it’s not the end of the world in an evolutionary sense. They’ve usually got lots of time to replace the population,” Alex explains.

But in the days of intensive guano extraction, important breeding grounds would have been disturbed by people near constantly, year after year.

Alex notes that with constant disturbance, we might expect a seabird to invest in its own survival and abandon a nest, rather than defending it. Different bird species are susceptible at different levels, but if the threat is severe enough, people’s actions can cause entire colonies to abandon their nesting sites.

For example, during the Namibian Guano Rush of the mid-1800s, up to 4,500 labourers at a time were working on tiny Ichaboe Island. This may have made it impossible for birds, such as Cape gannets, to breed successfully and possibly displaced them to other nearby islands.

Guano mining also destroyed the seabirds’ habitats.

When Namibia’s guano islands were first documented in the early 1800s, they were capped by several metres of bird poo. On Peru’s Chincha Islands, reports tell us that the undisturbed guano was up to 60 metres thick. Mining companies sought to scrape away every last inch of it.

While we may flush our waste away and forget all about it, the same can’t be said for birds. Guanay cormorants build their nests from guano and Humboldt penguins, African penguins and Peruvian diving petrels sometimes dig nesting burrows into it. Removing guano took away a resource these birds needed to survive.

Guano-producing birds were economically valuable, so measures were eventually implemented in the early twentieth century to protect them and sustain production. But this had consequences for other species.

Guards on Peru’s guano islands were tasked with shooting predatory birds on sight. These included gulls, vultures, peregrine falcons and skuas that ate ‘guano birds’, as well as their eggs and chicks. In February and March 1917 alone, marksmen reportedly shot more than 5,000 gulls on Peru’s southern islands. People also attempted to clean the islands by dumping tonnes of stones into the ocean, in the hopes of eradicating the ticks that fed on guano birds. 

South American sea lions were also nearly driven regionally extinct by guano mining. Hunting them was banned in Peru in 1896, as they were considered helpful to guano birds. But a change of opinion saw hunting restart in 1910. As many as 36,500 sea lions were killed in a single season, letting guano companies boost their profits by selling the fur, as well as guarding against a sea lion ever potentially harming a guano bird.

While this kind of conservation might seem extreme, Alex points out that it’s “something that’s still done in some places today because we value some species more than we value others, for whatever reason. Some of that can be economic, some of that can be aesthetic and some of that can be horribly biased.”

Why are seabirds important?

Losing large numbers of seabirds can have devastating consequences, not least of all the destruction of island ecosystems.

Guano is a vital resource in nature. The nutrients that seabirds transport from marine environments and concentrate on islands through their poo, feeds plants and diverse invertebrate communities. The nutrients also trickle back into the ocean, helping tropical coral reefs to grow and recover from bleaching. 

“When you lose the birds, you lose that input and that’s the bottom building block, the lowest row of your Jenga tower,” Alex explains. “They’re the foundation on which a lot of these island ecosystems are built.”

Guano extraction can’t be blamed entirely for historic bird declines. Overfishing has also played a part, with us taking away important food resources. Egg collecting and the hunting of some seabirds for their skins and oils has also had an impact.

But regardless of the cause, the outcome is the same – seabirds are ecosystem engineers and losing them has disastrous knock-on effects for the planet.

So, what’s the solution?

If guano mining is such a risk to seabirds and the planet, then surely we should just stop doing it? But when it comes to resource extraction, things are never that simple.

As Alex points out, it’s often a trade-off. If, for instance, we focused all our energy on extracting potash to use in fertilisers instead of guano, well that still comes with harmful environmental impacts. There’s another side to this argument too – that of the environmental damage caused by over-fertilisation.

It might sound quite gloomy, but there’s a bright side for guano birds. While we do still collect their poo, compared to the practices of the nineteenth and twentieth centuries, we do a much better job of looking out for these seabirds today.

For a start, most bird species in most parts of the world are protected to some extent.

Peru has designated numerous islands, islets and parts of their coastline as a National Reserve System. This protects not only the birds but other marine species in these areas too, including dolphins, sea lions and marine otters. The South Pacific islands the USA still claims through the Guano Islands Act have similar protections, making up part of the National Wildlife Refuge System.

Here in the UK, birds are protected by blanket regulations. By law, no one can disturb the eggs or nests of wild birds. Some species, such as white-tailed eagles, have additional protections. These kinds of laws exist in other parts of the world too – something Alex is very familiar with in his work on shearwaters and their plastic-filled diets on Australia’s Lord Howe Island. You need numerous strictly regulated licences and permits to work with these birds.

Today, bird guano isn’t the global phenomenon it once was – the industry has scaled back significantly. There are many more rules about where, when and how guano can be collected.

For example, guano scraping is no longer allowed on Namibia’s islands since the expiry of guano rights for Ichaboe in 2016. This leaves important nesting sites free for burrowing species such as African penguins. According to the Ministry of Fisheries and Marine Resources, guano that’s sourced in Namibia is taken from artificial platforms, such as the wooden Bird Island in Walvis Bay, and only at three-to-five-year intervals.

Guano went from being the protected prize of the Inca Empire to a devastating global commodity. While some issues may still remain, with the changes being made around the world to transform the remaining industry into something more sustainable and safe for seabirds, we’re hopefully heading in the right direction.