Malagasy Rainbow Frog

For its colouring. The Malagasy rainbow frog is patterned in a bold, high-contrast mix of white, black, brick-red or orange, and green, arranged in blotches and bands across its back, with a whitish belly. Against the pale sandstone of its canyon home the pattern is quite conspicuous when the frog is out in the open, which is unusual for a small burrowing frog. Whether the colours serve as camouflage against the mottled lichen-covered rock, as a warning, or as a signal is not well established, partly because the frog is so rarely seen active.

This one can, to a surprising degree. Most frogs that climb use sticky toe pads (like tree frogs); the Malagasy rainbow frog does not have those. Instead the tips of its fingers and toes are hardened into small, tough, spade-shaped structures — the same tools it uses to dig itself into sand. On rock, it presses these into tiny irregularities and cracks and hauls itself up near-vertical and even slightly overhanging sandstone in its narrow canyons. It is one of very few burrowing frogs that is also a competent climber, an adaptation to a landscape of deep, steep-sided gorges.

The Isalo region has a long dry season, and the rainbow frog deals with it the way many arid-zone frogs do — by burrowing into the sandy floor of the canyons and staying dormant, sometimes for months, until rain returns. When heavy rain fills temporary pools and floods the canyon bottoms, the frogs emerge quickly, feed, and breed explosively over a short window. Their tadpoles are adapted for this — they are filter feeders that hang in midwater sieving suspended food, and they develop fast enough to complete metamorphosis before the ephemeral pools dry.

Its entire range is a small cluster of sandstone canyon systems in south-central Madagascar, perhaps a hundred square kilometres of suitable habitat in total. Within that, its specific breeding sites — particular rock pools and canyon-floor flood zones — are few and vulnerable. The habitat is degraded by cattle grazing, trampling around water, fires set to promote pasture, erosion, and sedimentation of the pools, and some of it lies outside the protected Isalo National Park. On top of this, the frog's striking colours made it a target for the international pet trade before it was given the highest protection under CITES (Appendix I) in 2010. Small range plus specific needs plus collecting pressure is a dangerous combination.