When I ask my students to imagine an island, most of them picture something tropical with sandy beaches and lots of palm trees. My wife and I lived on just such an island in Hawaii for three years in the 1990s.
To anyone that studies ecology, islands hold special meaning and have helped unlock some basic understandings of how our natural world works. Darwin famously developed his theory of natural selection after visiting the Galapagos Islands off the coast of South America. He noted differences in birds on each island that correlated with differences in available foods. It was apparent that the birds shared a common ancestor but had changed after long periods of time in isolation on each specific island. Of course, there is more to the story but the point is that the effect was easier to note on islands with species that would not regularly migrate from their homeland.
 |
| Purple-faced Langur |
There are a few basic principles that predict the number of species that should be present on an island, as well as how different those species are from those found elsewhere. Size is an important consideration here. Larger islands should have more species than smaller islands and islands that are farther from the mainland typically have more unique species than those that are closer to shore. Both of these concepts have been studied at length with some of the earliest work done in the Everglades of Florida. Our family trip to Sri Lanka during the latest winter holidays illustrated these concepts perfectly.
Birds and mammals
Sri Lanka is an island nation off the southern tip of India. The main island is the 25th largest island in the world and is about half the size of New York State. It lies very close to the Asian mainland. In addition, its tropical location means that Sri Lanka has many species of plants and animals with a healthy percentage of them unique to the island. My wildlife watching is primarily focused on birds and mammals. Sri Lanka is a popular destination for both.
We arrived on Christmas Eve 2019 and spent the next 10 days travelling throughout the southern half of the island. Our guide took us to national parks, private tea plantations, the grounds of Buddhist monasteries and even small patches of trees in the midst of cities. After a full day of exploration, we would often go spotlighting in the evening to look for nocturnal animals (On one trip, I fell asleep and only awoke when we hit a pothole and I pitched into the aisle of our Jeep). I kept detailed notes and, as always, took as many photos as I could.
My checklists remind me that we saw 212 species of birds. Of those, 31 species are found only on Sri Lanka. Biologists use the term endemic when describing species that are found in a limited geographical range. This range can be rather large (as in the example “hummingbirds are endemic to the Western Hemisphere”) or rather narrow (some of the endemic birds we saw were found only in certain habitats on the island of Sri Lanka). In other words, about 15 percent of the bird species we saw could be found nowhere else on Earth.
We should have predicted that there were lots of bird species to see in Sri Lanka because it is a large island, but since it is so close to the mainland most of its species would not be endemic. Compare that to the Hawaiian Islands. They are much smaller pieces of land and had fewer native species (introductions and extinctions in modern times have changed the current situation drastically), however since Hawaii is so far from a mainland the majority of those species were endemic.
One of my favourite endemic bird sightings was the Sri Lanka jungle fowl. There are other species of jungle fowl in the world, one of which was domesticated and roams under the name “chicken.” Sri Lankans 
As expected, my mammal list was quite a bit shorter than my bird list. There just aren’t as many species of mammals as there are birds and many are harder to see. Of the 36 species I saw, six were mammals that are endemic to Sri Lanka. Although the numbers are smaller, the percentage of species unique to Sri Lanka remained the same as in the birds. We saw large mammals such as blue whales, Asian elephants and feral water buffalos, as well as small ones such as mice, rats and a deer-like species that reaches an adult weight of only five and a half pounds.
Purple-faced Langur
Our most exciting endemic mammal encounter was easily the purple-faced Langur. These monkeys are largely leaf-eaters, or folivores. Leaves can be very hard to digest so these Langurs have a very long intestine to help get the nutrients out of each meal. Often, they will eat the younger leaves because they have fewer toxins and are easier to chew. As Sri Lanka’s population grows, the remaining forested areas shrink, leaving the purple-faced Langur with less space to live. Not only is this species endemic, but it is endangered.
Efforts are underway to reconnect small patches of forest so this species will have access to more habitat. Losing the purple-faced Langur in Sri Lanka means losing it completely.
(Van Niel, an environmental conservation professor at Finger Lakes Community College, lives in Seneca Falls and enjoys exploring wildlife around the world as well as in his own backyard. He can be contacted at bears@flcc.edu.)
from daily news