A soaring albatross curves its wing and lands on a grassy peak on the edge of a cliff. “Plop”. It’s chicks wait for a mouth full of semi-digested fish. “Splat. Splot. Plish”. A penguin jostles from side-to-side “caplosh”, and another follows behind it “shlip”. And another “ssssphssphpt”. Every bird on this isolated chunk of land poos. The snipes, the gulls, the petrels and even the perfectly preened parakeets. As human beings, bird poo is something we generally avoid, especially the fishy kind. However, for Subantarctic islands, it is a vital ingredient.
Guano is the name given to sea bird (and seal) poo with regards to its use as a fertiliser. On Subantarctic islands, guano is the primary source of nutrients that gives richness to the soil, and that enables plants to survive. Guano is rich in potassium, nitrate and phosphate which are vital nutrients for plant growth. With a dose of bird poo Subantarctic plants can grow and then provide food for insects as well as unique terrestrial birds. In the case of the Antipodes Islands this means giving life to the Reischek’s and Antipodes parakeet as well as the Antipodes snipe and pipit.
Seabirds and seals get their food from the ocean, mainly in the form of fish. They then digest the fish and excrete all over the island when socialising, resting and nesting. In this way these animals transfer nutrients from the marine environment to the terrestrial environment. This process enables these relatively unproductive environments to flourish. Ecosystems on islands like the Antipodes are literally built on a foundation poo.
Insects help to decompose guano, which settles as a layer after rain, by eating and digesting the waste. In this light, the abundance of mice that feed on Subantarctic insects is a worry as a decline in insects may mean a disruption to the core nutrient cycles on the island.
So next time you feel unfortunate when a juicy white parcel of nutrients lands on your head, just think how happy you would be if you were a megaherb or a beetle on a Subantarctic island.