By John D. Altringham
2011-12 is the International Year of the Bat sponsored by the United Nations Environment Programme. Yes, that’s right – we are devoting a whole year to these neglected and largely misunderstood creatures. Perhaps if I give you a few bat facts and figures you might begin to see why.
There are approaching 5,700 species of mammal in the world – wallabies to whales, manatees to marmosets, tigers to tenrecs. A hugely diverse group, yet one in every five of them is a bat – that’s over 1,100 species. There are, admittedly, even more mice and rats, but to my (wholly objective and unbiased) mind, when you’ve seen one rat there are few surprises left among the rest. Bats, however, are wonderfully diverse. And they are just about everywhere – except the Antarctic.
Over 60 million years of evolution (early bats witnessed the demise of the dinosaurs) and the ability to fly and navigate in the dark, have given bats the means to occupy a huge range of ecological niches. Think of something edible and there is probably a bat that eats it: fish, fowl and amphibians, other mammals, a whole range of invertebrates including scorpions and crabs, fruit, nectar, pollen, leaves, nuts, and of course that most nutritious of substances that has given bats such a bad name – blood. In defence of bats as a group, I point out that only three species drink blood.
Because they fly, bats have an unusual life history strategy. For reasons I will not go into (read my book – it’s not what you think) the vast majority of bats give birth to only one baby and typically only once a year. Bats therefore have to live for a long time – much longer than they ought to for their size – if they are to keep their numbers up. A five gram shrew puts a prodigious effort into eating and sex for 12 months (if it is lucky) before dropping dead, presumably of exhaustion. A five gram bat may live for 10-25 years or more. The last time I looked, the record was a five gram whiskered bat that has returned to the same hibernation site each year for at least 43 years!
Lifespan is not the only way in which bats think big. Bats form the largest aggregations of mammals on the planet, with some caves being home to several million bats. At the other end of the scale there are small family units and even solitary bats. Most are highly social animals that use the landscape on an impressive scale. Stable social structures involving surprising levels of communication and cooperation are common. These complex societies persist despite frequent roost switching, the need to forage over large areas and in many species the necessity of long seasonal migrations.
Bats are important in a wider conservation context. We have known for a long time that fruit bats in both the Old and New World tropics are important pollinators and seed dispersers – we are only just beginning to document the crucial role they play in tropical forest regeneration and maintenance. They are economically important pollinators of a wide range of fruits in the Old World tropics and their contribution to the US economy as controllers of insect pests was recently valued at $23 billion dollars per year, perhaps as much as $50 billion. Bats have most of the attributes needed of a good biodiversity indicator group – widespread, ecologically diverse, lots of species, high in food webs, ecosystem service providers, etc. Monitor the health of our bat populations and we get a good insight into the health of the environment in which they (and we) live.
And if that’s not enough, they have ‘engineering’ skills to astound and inspire us. It was recently discovered that echolocating bats make use of ‘parallel navigation’ to track and catch their insects – a technique only recently mastered in the most sophisticated guided missiles. I could go on…
So, why have bats had such a bad press until recently? I think Bram Stoker has a lot to answer for. In European traditions, pre-Stoker, vampires took many forms – but very rarely that of a bat. In cultures across the world bats (with a few exceptions) traditionally had and have a positive image. In China the symbol of good luck, the Wu Fu is a peach tree surrounded by five bats, representing health, tranquillity, wealth, good fortune and a long life. May you be blessed with all five and an informed appreciation of bats.
John Altringham is Professor of Animal Ecology and Conservation at the University of Leeds, UK, where he has been since 1989. He completed his BSc at the University of York, and his PhD at St. Andrews University, where he returned as a research fellow from 1983-1989. During his career he has travelled widely, studying animals as varied as tuna fish and tarantulas before focusing on bat ecology and conservation. He has published over 100 scientific papers, numerous book chapters, and two previous books: Bats: Biology and Behaviour, and British Bats. He is also a regular advisor and contributor to BBC Natural History Unit productions for TV and radio, and is a member of a number of conservation advisory groups, including the Nature Conservation Panel of the National Trust. His most recent book is Bats: From Evolution to Conservation.