La Grille is the extinct volcanic massif that dominates the northern part of Ngazidja. This site extends from the summit (Saondzou, 1,087 m) down to an altitude of 800 m. This includes nearly all of the area used by the restricted-range bird species present on the mountain, and all the forest. Relief is gentle, but interrupted by small (less than 1 km) raised craters, although the northern part of the mountain is steeper. The habitat is mixed montane (evergreen) forest, all of which is underplanted, apart from relict patches inside craters. The lowest parts of the site and its surroundings support cultivation including tree crops (mostly traditional practices, but also a farm established using overseas investment), secondary forest and grassland with bracken Pteridium aquilinum (especially to the south). A Eucalyptus plantation (probably dating to the 1940s) abuts the forest to the north-west.
See Box and Table 2 for key species. La Grille supports a subset of the bird community of Karthala. Forest species absent include four of the five Ngazidja endemics (the one present is Nesillas brevicaudata), and other Karthala (KM001) lowland specialists. The two species of conservation concern are both near-threatened; Circus maillardi has not been documented at the site, but is certain to occur; Columba pollenii and six others are also restricted-range species, and two (Turdus bewsheri, Foudia eminentissima) show higher population densities here than on Karthala. Nine Ngazidja-endemic and five Comoro-endemic subspecies occur. The eucalyptus plantation is of no importance for birds.
Non-bird biodiversity: Evergreen forest may show differences from Karthala, but is hardly studied. Butterflies: six Ngazidja- and two Comoro-endemic species; two threatened: Papilio aristophontes (EN), Graphium levassori (EN). No data on other taxa specific to this site.
BirdLife International (2019) Important Bird Areas factsheet: La Grille Mountains. Downloaded from http://www.birdlife.org on 17/11/2019.