their lowest, much of the Sunda Shelf was exposed. This linked what are now discrete islands (including Borneo, Java, Sumatra, and a host of smaller islands) with the Malay peninsula in one large landmass known as Sundaland. During periods when the shelf was exposed, birds could move freely across the whole landmass. When the waters rose again, these birds were cut off from their relatives, and evolved in isolation on the various islands. Temperatures were cooler overall during glacial periods, so montane birds (those generally restricted to the slopes of mountains) could move lower and spread across larger areas. During interglacial periods, they retreated to higher elevations and were separated again from other populations, including birds in the lowlands. Studies have shown that some endemic montane species are most closely related to species in Borneo's lowlands, while others are more closely related to montane species on other Sundaland islands. Endemism and threats The island is home to a single endemic family: Pityriaseidae, which contains a single endemic genus (Pityriasis) with a single endemic species, the Bornean bristlehead. In addition, the island holds two other endemic genera, both of which are also monotypic: Chlamydochaera (the fruithunter) and Haematortyx (the crimson-headed partridge). Two other monotypic genera formerly considered to be endemic to the island—Chlorocharis and Oculocincta—have since been merged into more widespread genera. Chlorocharis was merged into the large white-eye genus Zosterops after molecular studies showed it nested comfortably within that genus. The same studies showed that Oculocincta was embedded within the smaller white-eye genus Heleia, leading it to be moved as well. There are 59 endemic bird species on Borneo, according to the taxonomy proposed by the International Ornithologists' Union. Nearly all of these are forest birds; only the dusky munia is not. In all, roughly 10% of Borneo's forest birds are endemic to the island. Of these, 60% are montane species, 30% are found on lower slopes, and 10% are lowland species. However, Borneo's forests are under threat, particularly in the lowlands. Nearly 40% of the island's forests had been completely cleared by 2016, and another 34% had been selectively logged. Some 80% of Kalimantan's forests have been sold to timber concessions. Much of the original lowland forest has been converted to palm oil plantations; these now cover more than 32% of Kalimantan's lowland area. This results in a huge loss of biodiversity. While the original dipterocarp forests are home