They say that when Marconi explained to his family that he wanted to try and send wireless signals over long distances they packed him off to a psychiatric institution for a check up! If we hadn’t done our background reading before, we would have been just as sceptic when Dianne Odegard from Bat Conservation International explained to us that her husband follows bat movements at Bracken Cave with the local weather radar.
We visit Dianne and Lee Mackenzie at home so that they can show us how this technological miracle works. Our visit, however, begins with the presentation of a large number of winged guests that fill several corners of their house and garden. Dianne and Lee’s lives revolve around bats and they have set up in their house a field hospital for the wounded animals they find in their area. Whilst Lee shows us the flight cage in the garden, where bats are allowed to fly before being released, Dianne feeds a free-tailed bat with maggots. Seeing it from close up, so small and frail, it is hard to imagine how it can be picked up by radar signals during its night-time flights — although the fact that it flies in the company of millions of fellow bats does make it a bit easier to understand!
The idea of using the weather radars to detect bats was developed by Thomas Kunz, probably the most brilliant and original of all bat researchers. He studied their movements and those of their prey in the atmosphere and proposed a new ecological discipline that attempts to understand the complex interaction between animal species in a constantly changing environment such as the atmosphere. He named his new discipline aeroecology.
The radar images that Lee shows us on his computer are the result of Kunz’s pioneering work. Each morning Lee enters the website of the MRMS (multi radar sensor-system), a joint venture run by a number of US research institutions that offers open access to atmospheric phenomena throughout the whole country, and which is also able to monitor bat movements. The interpretation of the images is not easy and a good dose of both practical experience and knowledge of the local climate is necessary to avoid confusing a real cloud with a ‘cloud’ of bats. In any case, Lee is able to interpret with great precision the images on the radar. He shows us how the day before a weather front from the east dragged a vast cloud of insects from agricultural regions into inland Texas. The bats made good use of this phenomenon and travelled less far than usual to feed. Just a few hours after night had fallen, the dense cloud of bats covered an area of dozens of square kilometres as it fed on this ‘manna from heaven’ that the wind had brought with it.
Lee, who insists that he is not a scientist but just a bat lover (that’s a bit hard to believe), records every day the emergence times of the various mass bat roosts in south Texas (Bracken Cave, the bridge in Austin, Frio Cave, etc.) and measures the maximum size of the various bat clouds as a means of inferring the number of bats, while at the same time taking careful measurements of environmental conditions (temperature, wind speed, atmospheric pressure, and a whole series of other variables) around each cave. His data series, rigorous and unbroken, are beginning to grow. Hi-tech popular science! The ever-present smile that is always on the face of this energetic and enthusiastic man disappears abruptly when we ask him what would happen if all the bats that he follows with such passion suddenly disappeared. “It would be a disaster – let’s just hope that it never happens.” The ‘disaster’ that Lees refers to would be a major problem for economic and public-health reasons. The new discipline of aeroecology enables us to quantify robustly the economic value of bats and the cost that their disappearance would have for farmers. The ecological service provided by bats would have to be replaced with pesticides, which would have highly negative effects on public health, and mean a bill of 700,000 dollars for the cotton farmers in south Texas alone, and of 3,700 million dollars for the USA as a whole. A price can now be put on what was once the intangible value of a small part of the natural world that surrounds us. Given the magnitude of these figures, it would not be a bad idea if the architects of our economies took it to heart.