Across Water and Forest: The Chameleon of Ankaratra

Calumma hilleniusi is a rare chameleon species endemic to Madagascar, described by Brygoo and Domergue in 1973. It is restricted to the Ankaratra Massif in the central highlands, making it a true microendemic with an extremely limited distribution. The species inhabits montane rainforest fragments at high elevations, where cool and moist conditions prevail. Its confinement to a single mountain range highlights its vulnerability to habitat loss, fire, and climate change, all of which threaten the fragile ecosystems of Ankaratra.

Morphologically, Calumma hilleniusi is a medium‑sized chameleon with adaptations suited to dense vegetation. Like other members of the genus, it is oviparous, although detailed reproductive biology remains poorly documented. Its ecology is closely tied to intact forest interiors, where it relies on camouflage and deliberate movements typical of arboreal reptiles.

What makes Calumma hilleniusi unique among chameleons is its locomotor behavior. It is the only species reported to actively walk through water, with individuals observed deliberately wading across shallow streams. This unusual trait sets it apart from all other known chameleons, which generally avoid water crossings.

The species is listed on the IUCN Red List, reflecting both its restricted distribution and the threats it faces. Although it occurs within a protected area, its microendemic status means that any disturbance in Ankaratra could have severe consequences for its survival. Calumma hilleniusi stands as a striking example of Madagascar's exceptional herpetological diversity, combining rarity, ecological specialization, and a behavioral trait found nowhere else in the chameleon family.