Arenillas Ecological Reserve, Nature reserve in Huaquillas, Ecuador

Arenillas Ecological Reserve covers 17,083 hectares in El Oro Province, in the Arenillas and Huaquillas cantons near the Peruvian border. It protects one of Ecuador's largest remaining areas of dry forest and scrub, with deciduous lowland forest and tropical dry shrubland that becomes shrubbier toward the coast, where 2,800 hectares of mangroves grow. The reserve is also a military zone.

Arenillas was declared a protection area over 60 years ago, but official recognition came only in 2001, when it joined Ecuador's National System of Protected Areas. The Fundación Ecuatoriana de Investigación y Manejo Ambiental (FEDIMA) carried out the technical studies and compiled the information behind the declaration. Because it also serves as a military reserve, the Ministerio de Defensa Nacional administers it.

The reserve's name comes from the Arenillas and Huaquillas cantons it spans in El Oro Province. In its buffer zone the Fundación Cerro Verde works with a local management committee made up of 36 registered communities, running environmental education activities using the Ecology Study method. The grey-cheeked parakeet, one of the reserve's endangered birds, can be seen in the mangrove areas.

Access requires prior permission from the Ministry of Defense, which administers the reserve as a military zone; arrange it before travelling. There are no marked public trails, so visitors move with authorization and guidance. The climate averages around 24 °C, and the dry scrub and deciduous forest offer little shade at midday.

The grey-cheeked parakeet, one of the reserve's endangered birds, nests in cavities in the dry forest; the reserve is a BirdLife International Important Bird Area, and 35% of its 153 recorded bird species are endemic to the Tumbes region.