Biology Reference
In-Depth Information
In that September of 1986, before we had our first successful radio-collaring, torrents of rain
had engulfed the Chitwan Valley for three solid days. Along the banks of the Rapti River, vil-
lagers gazed in wonder and fear at the surging brown floodwaters that swept uprooted trees
along as if they were toothpicks. As I stood watching above the river's roar, the ecological
significance of this event became clear. Floods occur here almost every year, but rare, cata-
strophic floods are the major structuring force in the one-horned rhino's home ecosystem,
redrawing the vegetation map. Had I not been here to witness this rare event, I might have
missed seeing how a once-in-a-century or half-century deluge inundates vast areas, reshaping
the ecology of the land. Such a flood reconfigures floodplains and oxbows and even shifts the
vegetation types over huge areas through the deposition of rich silt carried from the moun-
tains.
Every year, monsoon flooding forces the wildlife of the Terai zone to head to higher
ground or risk being swept away. When the threat passes, however, new life emerges. As
each year's flood-waters recede, the silt deposited in the grasslands acts as a layer of fertil-
izer. From that silt, the next year's crop of wild sugarcane will emerge, and rhinos will feed
on the shoots. The ability of greater one-horned rhinos to feed on early postmonsoon veget-
ation maintained by annual disturbance, to track those disturbances, and to disperse among
them is vital to their survival.
Fortunately, river-hugging rhinos are powerful swimmers. They can easily ford the flood-
ing waters and are savvy enough to avoid exposed quicksand when waters retreat. Not all of
Chitwan's grassland-dependent mammals handle the floods with such aplomb, however. En-
dangered hog deer are sometimes washed away by the rising waters. The elusive pygmy hog
and hispid hare, also called the bristly rabbit, are some of the rarest mammals on Earth and
face emboldened predators when floods bury their tall grass cover. Yet such native species
must have made some adaptation to the normal range of annual flooding and the once-in-a-
century deluges, as species truly unable to cope would have vanished ages ago.
Today, one still finds very large mammals in the tropical belt where a deadly disease such as
Ebola, malaria, or dengue fever is rampant, where the soil is infertile, or where both condi-
tions leave the landscape better suited to wildlife than to human habitation and agriculture. In
other places, such as sub-Saharan Africa, outbreaks of diseases such as rinderpest and sleep-
ing sickness, carried by the tsetse fly, spread among livestock and their herders, preventing
both from occupying natural habitats. Until 1950, a deadly strain of malaria kept the Terai
zone habitat of the one-horned rhino in Nepal and India virtually free of humans and rel-
