Intro: Conservation

The conservation status of the different species of gliding mammals varies enormously, ranging from critically endangered to least concern. Of the 65 species of gliding mammals there are two considered critically endangered, six are endangered, three are vulnerable, five are near threatened, and 32 species are classed as of least concern. A reflection of the poor knowledge of this group of mammals is that 11 are considered data deficient and six have not been evaluated due to their recent recognition as species. The primary threats faced by gliding mammals throughout their distribution include loss of habitat as a result of clearing of vegetation for timber and agriculture, the naturally limited distribution of some species, hunting for food, occurrence of frequent fires, and their collection from the wild for the pet trade.

The indication from the species with a conservation status of ‘least concern’ is that these species face little or no threat. Sadly this is almost certainly not the case as most species are in decline in at least part, if not all, of their distribution. It is highly likely that many more species and subspecies should be recognised as vulnerable or endangered but are not due to the limited information available and the difficulties associated with species that have a large geographic distribution over a continent and/or multiple countries.

For example, the Siberian Flying Squirrel is considered low risk near threatened overall. However, in Finland and elsewhere, populations have declined severely during the past few decades as a result of intensive forestry that has removed old hollowed trees.

Similarly in Estonia the Siberian Flying Squirrel’s distribution has declined considerably, with one study showing numbers at five monitoring sites having declined by 21 per cent between 1940 and 1979 and almost 50 per cent during the period between 1980 and 2001. As a result of habitat loss the species is vulnerable in Finland, endangered in Estonia (with only a few hundred animals remaining), and possibly extinct in Latvia, Lithuania and Belarus. In Korea it once occurred throughout most of the northern half. However, due to clearing in the 1960s and 1970s there was a serious decline in numbers and range, resulting in it occurring in only very small numbers throughout its former range and was listed as Endangered in 1982.

Similarly, the Northern Flying Squirrel and the Southern Flying Squirrel from North America each has subspecies that are considered threatened. Therefore it is likely that a more detailed analysis of the distribution of each species and subspecies level within each country is likely to reveal many more threatened populations.

As all species of gliding mammals are arboreal they are typically limited to crossing small gaps in the tree canopy. Although they can glide over some gaps such as roads, tracks and power line easements, they cannot move easily through areas where the trees are more widely spaced than their maximum glide distance, which is typically only 30–60 metres (depending on the height of the trees they launch from and the surrounding terrain). Therefore gliding mammals are highly sensitive to habitat fragmentation as they do not readily travel along the ground. If they do come to the ground they are exposed to an increased risk of predation. One method which has been used to assist gliding marsupials in Australia has been the placing of power poles on each side of roads which the gliders can use to bridge gaps in the vegetation.

One of the key reasons for raising concerns of the currently recognised conservation status of different species of gliding mammals is highlighted by South-East Asia. This region includes approximately half of all species of gliding mammals, yet it has the highest relative rate of deforestation of any major tropical region and could lose three-quarters of its original forest by 2100 and up to 42 per cent of its biodiversity. The conversion of natural habitat to other land uses is considered the major driving force behind worldwide biodiversity loss.

One of the immediate impacts of logging activities is the alteration of the unique multilayered and closed tropical canopy. Observations in Malaysian forests show that reductions in canopy height, surface area and the crown size of selectively logged forests are still evident after four decades of regeneration. When these forests are cleared the species richness of trees appears to be negatively associated with the intensity of the logging activities, suggesting that logged forests require long periods of time to recover. Similarly, recent studies show a trend of declining species richness and population density with increasing forest disturbance through logging activities, agriculture or urbanisation across a range of South-East Asian taxa, including mammals.