The slender-billed thornbill

Most birds worth looking for announce themselves — a flash of colour, a carrying call, a shape stamped memorably against the sky. The slender-billed thornbill does none of this. It is small, brownish-grey, streaked in the unhelpful way of a dozen other small brownish-grey birds, and it keeps almost entirely to the low, salt-crusted scrub of the samphire flats, where it works quickly through the Tecticornia glassworts after insects and seeds and rarely gives you more than a second’s clear look. You are not likely to find it by its beauty. You find it, if at all, by knowing exactly where to stand.

Where to stand is the whole story. This thornbill is a Gulf St Vincent specialty — a subspecies found nowhere else on Earth — built around samphire, confined to the dense, low, salt-tolerant shrubland that fringes the gulf’s tidal flats. That fidelity shows what a halophyte community offers: a whole architecture of cover and food that one small bird has come to depend on absolutely. Lose the samphire, in any patch, and you do not get a diminished thornbill population there — you get no thornbill at all. It is exactly this kind of narrow, non-negotiable habitat requirement that gets a species listed: the slender-billed thornbill (Gulf St Vincent) is recognised as vulnerable, close to a textbook case of why habitat clearance and fragmentation are the sharpest edge of extinction risk for any narrow specialist, rather than any direct persecution of the bird itself.

Which makes the samphire’s own condition the thing worth worrying about. Gulf St Vincent’s saltmarsh is losing ground at its seaward edge, drowned faster than it can recolonise landward as sea level rises, and Australia’s coastal saltmarsh generally is now a formally listed threatened ecological community — squeezed, historically, by drainage and reclamation, and squeezed now by the sea itself (Delta 2017; Saltmarsh 2013). A bird this tightly bound to one threatened habitat has no fallback address.

There is, even so, an encouraging postscript. When surveyors went looking properly in 2024 — combing the samphire with more effort than this quiet little bird had ever been given — they turned up around 620 individuals across a dozen sites, well beyond the handful of locations the old records held (Green Adelaide 2024). Read that carefully: it is better knowledge, not a reprieve. The bird is still listed, still rare, and still entirely dependent on samphire that is still losing ground. But it is hanging on in more corners of the gulf than anyone had counted — which is, for a species this narrowly built, about the best news going.