Guano enriches man and plants, sometimes too much

OPINION

The 804 million penguins, gulls, shags, albatrosses, pelicans, petrels and other seabirds of the world take 3.8 million tons of nitrogen out of the sea and poop it on land every year. These birds and their chicks also bring nearly 100,000 tons of phosphorus ashore annually.

So calculate Xose Luis Otero and his colleagues at Santiago University, Spain. They were interested in quantifying the role of seabirds in cycling nitrogen and phosphorus around the globe and boiled down a huge data set to make the calculation.

Birds don’t produce urine. Instead they make a white pasty urea with which they plaster the ground around their roosting and nest sites. This is especially true in and around Antarctica, where millions of breeding penguins enrich the surrounding seas.

In rainy places, the poo quickly washes away, but in parched parts of the tropics the stuff accumulates for centuries and sometimes millions of years. This is especially true of Peru and Chile where vast deposits of guano accumulated, sometimes to a depth of 100 metres.

In the 1840s, Peru grew wealthy by importing more than 10,000 Chinese labourers to mine the deposits. Few of the Chinese survived long enough to return to their homeland.

Huge quantities of guano were exported to Europe where it was used as a farm fertiliser. As the Peruvian mines were worked out, Chile virtually monopolised the guano trade, but by the early 1900s the South American mines were nearly exhausted.

Fortunately, in 1908, the German chemist Fritz Haber invented a technique for extracting nitrogen from the air and turning it into urea. In doing so Haber averted worldwide starvation, winning the Nobel Prize in 1918 for his discovery.

These days the biggest guano deposits are in China, the US and Morocco.

Morocco’s deposits cover 4500 square kilometres and, at more than 60m years old, were produced, not by birds, but by dinosaurs.

From the edge of the Sahara desert, Morocco’s phosphate-rich guano travels on a 61km conveyor belt to the nearest port to be shipped around the world, including New Zealand.

Because New Zealand is so rainy, most birds perch in trees so long that seabird droppings are washed away and very little accumulates in any quantity except at our gannetries (gannet colonies).

Mind you, some birds spend so much time that they kill the trees they roost or nest on. Shag droppings killed all the trees on tiny Whero Island in Foveaux Strait, ruining the island as a sanctuary for other seabirds.

Nesting or roosting shags have also killed a number of macrocarpa trees in the North and South Islands.

Overnight roosting starlings killed pohutukawa trees in Wellington, then moved on to a couple of Norfolk pines in Pigeon Park, which they also killed in the 1970s.

On the other hand, seabird poo enriches certain soils and encourages the growth of rare or endangered native New Zealand plants.

Factoid: In Japan, nightingale poop is mixed with bran and used as an exfoliate.