Bats on radar!

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.

Dianne looking after a bat to ensure it shows up on the radar again
Dianne looking after a bat to ensure it shows up on the radar again
Lee Mackenzie showing us the flight cage
Lee Mackenzie showing us the flight cage
One of the occupants of the flight cage
One of the occupants of the flight cage
Lee shows us how the bats extend over the Texas sky
Lee shows us how the bats extend over the Texas sky
Detail of the bat cloud a little before midnight
Detail of the bat cloud a little before midnight
Lee and Dianne with the film crew
Lee and Dianne with the film crew

Attracted by superlatives – Bracken Cave

There are places that nearly every one dreams of going some day — the Great Pyramids of Egypt and the Eiffel Tower figure high on the list of sites that many would like to visit. For bat-lovers, the list is topped without any question by Bracken Cave.

Bracken Cave is unparalleled as the largest known congregation of bats anywhere in the world. A magnificent spectacle for all — and we can’t find it! Our anxiousness grows as the afternoon draws on and we are unable to interpret the simple map we have and find the turning that leads to the cave. We’ve searched for it everywhere on the GPS but it’s not there — like it or not, on this occasion this jewel of modern technology is of no help. Bracken Cave is the Mecca of bat-loves but does not appear on the maps since its custodians make sure with great efficiency that it is not over visible. Frankly, we didn’t expect that. Given the size and importance of the cave we expected well-lit signs on the motorway between Austin to San Antonio in southern Texas, which would take us to the doors of the cave itself. After a number of false starts, out of sheer desperation we stop at a petrol station that is in theory near the cave. The person has heard of the cave but can’t tell us where it is; the second knows where it is but says it’s difficult to get there because “they got it well hidden”. Nevertheless, his directions get us there in the end in time to see the show begin.

We join a group of thirty visitors that are allowed to approach the cave today. Mylea Bayless, Director of Conservation Programmes of Bat Conservation International (BCI) is waiting to show us around. The zeal with which the BCI protects this essential site is well justified due to the pressure from housing schemes and the fact that uncontrolled visits could negatively affect the bat colony. Since they bought the cave and the surrounding land the efforts of the BCI have centred on controlling and regulating visitor access and on improving the natural surroundings. Our impression is that they have managed to fulfil both objectives very successfully. Along with Mylea there is a small group of local volunteers who accompany us on the visit and help visitors. It’s 6 o’clock in the afternoon as we reach the cave. Visitors sit on wooden benches installed by the BCI that help remind us that we have come to see what is, after all, natural show. Each bench has a metal plaque with the name of the person who paid for it. Then, Don Bergquist, a BCI volunteer who is retired, makes a long introduction, both rigorous and humorous, to the world of bats, using his voice and a few photos as his main tools. He turns what promises to be a wonderful show into an educational spectacle as well. Whilst Don is talking the first bats begin to appear and the public’s attention turns towards the entrance to the cave.

The 10-metres-long entrance to the cave is in a small depression in the ground and through it around 15 million Mexican free-tailed bats (Tadarida brasiliensis) leave every evening. They gain height in a dense frenetic spiral and fashion an impressive formation that snakes its way away towards the far horizon. The emergence can last up to 4 hours as not all bats can leave at once; thus it begins quite early, before the sun has even set. The sheer number of bats, the speed and the grace with which they fly in front of us, and the sound of their wings beating all captivate us for a while. We leave in the end when there is no more light left with which to see the many millions of bats still to leave their cave.

Once witnessed the magnitude of the spectacle, it is understandable that the BCI uses all its resources and volunteers it has to preserve this cave. The threat of a new housing project next to the land that harbours Bracken Cave has raised the alarm. Mylea explains that the buildings themselves will not directly affect the bats but will multiply exponentially the amount of contact between the bats and humans, which will have unforeseeable consequences for the cave and its occupants.  The BCI has decided to avoid all conflict and Mylea is sure that the NGO will be able to raise the near 20 million dollars that it needs to buy the land and in this way prevent the building from going ahead. After having met them, we too are convinced that they will manage to raise the money.

Entrance to Bracken Cave
Entrance to Bracken Cave
Expectation as the first bats fly out
Expectation as the first bats fly out
One of the wooden benches donated by members of the BCI
One of the wooden benches donated by members of the BCI
Don Bergquist explaining the miraculous lives of bats
Don Bergquist explaining the miraculous lives of bats
Don observing the river of bats
Don observing the river of bats
Emerging from Bracken Cave
Emerging from Bracken Cave
Emerging from Bracken Cave
Emerging from Bracken Cave
Mylea Bayless talking with the team
Mylea Bayless talking with the team
Last light at dusk over Bracken Cave
Last light at dusk over Bracken Cave

Bridge over the river Colorado

“It’s important to hydrate!”, “Water is vital!”, are just two of the slogans shouted by Cory Roussel as he crosses the bridge on Congress Avenue, full of expectant onlookers leaning against the bridge rail. According to the US Weather Agency, in Austin, the capital of the state of Texas, temperatures only rise above 38ºC 18 days a year. It’s August and it’s one of those days and perhaps for that reason we decide to heed his words. Even though it’s already six o’clock in the afternoon, it’s still very hot and the hundreds of people on the bridge enable Cory to sell 100–200 bottles of water every evening, he tells us contentedly. This small financial help means that he can earn a living working just evenings from March to November for as long as the bats are present. Cory has grown a contagious passion for bats, and besides selling bottles he’s ever willing to educate and help the bridge’s visitors.

His business depends on a maternity roost of Mexican free-tailed bats (Tadarida brasiliensis) that occupies the fissures in this bridge over the river Colorado, and which every night attracts hundreds of people to watch the bats from every conceivable vantage point: from under and on the bridge, from the river banks or even from boats of all types on the river. The modest Texan river Colorado has not left its mark in the same way as its larger namesake has further east between the USA and Mexico, but does nevertheless still offer a unique natural spectacle of a different type. Up to 1,500,000 of these bats come to this bridge over the river Colorado. Even by day, our noses and then our ears first notice their presence as we get closer to the bridge. At dusk the bats abandon their safe shelter to fly to neighbouring agricultural areas where they will feed on the insects that fly there. They form a long procession that trails off towards the horizon and, with the last light of the day and the silhouette of the modern city centre behind them, it is a truly unreal sight. A strange but harmonious blend of neon, skyscrapers and wildlife make this a natural show that is light years from the idea of pristine nature — but it is not for that any the less attractive. The approximately 140,000 visitors that annually come to see the bats are testimony to that.

Corey’s business is a good example of how the largest urban colony of bats in the USA generates economic benefits that Bat Conservation International (BCI) calculates at 8 million dollars a year. The main benefactors are the restaurants, hotels and the transport sector. Visitors are mainly Texans, but also come from the rest of the USA and other parts of the world. Dianne Odegard, the BCI’s energetic Public Education & Training Coordinator, welcomes us fulsomely underneath the bridge and explains the history of the colony and the long fight by the BCI to save it. The work of this NGO can be summed up as a continuous series of awareness-raising efforts that since the 1980s have changed people’s perception of bats from rejection to acceptation.

Homage to the bats on Congress Avenue Bridge
Homage to the bats on Congress Avenue Bridge
‘Bat-signs’ in the city
‘Bat-signs’ in the city
Bats and marketing
Bats and marketing
‘Please head left to see the bats’
‘Please head left to see the bats’
Expectation on land and on water
Expectation on land and on water
On the bridge at dusk
On the bridge at dusk
Bat make-up for the youngest observers
Bat make-up for the youngest observers
Bats leaving the bridge
Bats leaving the bridge
The bridge at work
The bridge at work
The show is over
The show is over