Arid deserts, scrubby woodlands, cool mountains, and steamy rainforests all constitute hornbill habitat. In general, however, hornbills are birds of the forest. Of the 30 species found in India and Southeast Asia, only the Indian gray hornbill lives in open savanna. In Africa, where forests are less extensive, the proportion of savanna-dwelling species increases accordingly; 13 of 23 species reside in savannas and woodlands while the remaining 10 inhabit forests. Species occupying savannas tend to have more extensive ranges but, like the red-billed hornbill, may be separated into many distinct populations by imposing bands of woodland. Endemic species are, by default, limited to habitats available within their restricted range. This is particularly true of insular species like the Sumba hornbill, which occupies all forest types on its native island.
There are key features that must be present in all hornbill habitats—an ample number of large trees for nesting, an adequate year-round supply of food, and enough habitat area to support a viable population. Each species has a particular set of requirements, which may help explain why several species can simultaneously occupy the same habitat. In the forests of Thailand, where nine hornbill species may occur together, a small Tickell's brown hornbill (Anorrhinus tickelli) is able to use nest holes of smaller dimensions than the larger great hornbill (Buceros bicornis). On Sumatra, where a similar number of species coexist, they generally forage on different diet items; when diet overlap occurs, as with rhinoceros and helmeted hornbills, they partition their habitat by feeding at different heights in the canopy. Habitat quality will influence the number of hornbills an area can support. Habitat size also limits hornbill populations. On the island of Sumba, hornbills are rare or absent from forest patches less than 3.6 mi2 (10 km2) in size.
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