Science cover, vol 377, No 6604. Species tend to live in narrower slices of mountainside on tropical versus temperate mountains. Stronger competition in the tropics explains this pattern for birds. For example, the habitable range of this white-tipped sicklebill (Eutoxeres aquila) is limited as a result of competition with its close relative, the buff-tailed sicklebill (Eutoxeres condamini). See page 416.
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