Bats and Bridges

Introduction:- Bats are often referred, read and shown in the mystery story, comics and suspense thriller films. A common man is usually afraid of Bats! But the fact is too different. Bats are perhaps the only tiny mammal left on the earth which can fly; in daytime bats hang-up themselves in inverted position (head below) under trees / cracks and crevices, gaps in stones, caves or under roofs of old houses and bridge decks; in nights they fly in search of fruits, flowers, insects, small frogs, lizards, tods and butterflies etc. thus manage the environmental cycle.

The wastes generated by bats below trees / soil below bridges is a fertile manure. However they live a bad smelling stains on undersides of roofs of bridges. Many people are afraid of bats with an assumption that they might attach human or so. But bats never attach of humans nor harm them of any kind. In fact, it is a human who often kills bats in villages for medicinal uses (which are unscientific and unproven). Unlike other flying creatures, bats are hot blooded, there are several verities / species of bats found all over the world. But due to lack of knowledge and preservation many of the rare species are in danger today! increasing pollution, reducing trees / jungles; increasing white lights in cities even at nights, reducing natural food; increasing infectious deceases, reducing awareness among people are the primary reasons behind the diminishing species on the planet!

You may be aware of the famous Austin city and it’s olden bridge were worlds largest population of the bats colonies resides and proudly preserved by government since several decades. These bats come out in the evening just before sunset in lakhs of numbers to search for the food for their newborn babies (one bat given a birth to one baby every year). Entire skyline gets filled with a cloud of drizzling bats and their humming sounds ‘chi’ ‘chi’ ‘chi’ . . . everyday thousands of visitors from all over the world, gather on the old Austin bridge, nearby gardens, in boats in river below, every evening to see this amazing phenomenon. There are several in-accessible caves, in juggles in various nations of the world, where bat colonies do reside in big strength. But Austin is the unique example where the colonies are found in the living habitable areas. Usually bats are extremely sensitive mammals; they cannot sustain frequent and wide environmental changes (temperature, humidity, lights, sounds etc.) hence prefer cooler to warmer isolated quiet areas of land / jungle / water bodies etc. away from city noise / light / air and water pollutions. During hung position bats frequently keep flipping their wings to generate coolness. 

You may be aware about the recent locusts (grasshoppers) attacks on Rajasthan and many other states in India as well as abroad. The locusts fill the skylines and travels for long distances of several kilometers a day and attack the fresh farms and eat then voraciously, merely couple of hours! This causes food grain crises for the humanity. The locust attacks are very much dangerous and worrying phenomenon as the colonies of locusts form a long chain ranging upto several kilometers and travels all over the oceans. A few sparrows or lizards cants control them neither the drone sprays chemicals!! (in fact, chemicals lead to several other problems to human health – a domino effect!) the small bat species can effectively attack the locust clouds and keep a check and balance on their numbers!

Bats also help distribute the seeds of many important plants, so they can reproduce and create more fruit for humans to eat and enjoy. Without pollinating and seed-dispersing bats, many ecosystems would gradually die. Bats also eat large amounts of mosquitoes; they help control viruses spread by the insects.

In the present article the author has presented the unique relationship between the Bats and Civil engineering structures - presence and preservation of bats below the structures, mainly the bridges. This will be helpful for the budding bridge engineers in their restoration projects in career ahead.

General:- I heard first time about the bats below bridge and their preservation from one of my friends in USA way back in year 2010. He worked in Caltrans; there in bridge preservation / retrofitting program the inseparable part is of bats’ preservation. I couldn’t believe the sensitivity and care for the nature at that time. Later in 2013 Dr. Anwikar from Germany presented one of his unique bridge restoration projects in Germany where he also mentioned about restoration about the bats’ abode. At that time couple of our seniors were astonished and a few even laughed! (because for Indian civil engineers, this topic was new as well as there was no awareness about the sensitivity of the environment). Later couple of years I researched over the topic. There are several techniques to move / navigate the bats from old bridge to the new location and after bridge repair is done then navigate the colony back to original locations (like creating aerodynamic disturbance or giving food etc.). Today while preparing a draft of my new paper of structural audits for bridges and infrastructure (which is coming up soon), I came across a book titled ‘Bridge Maintenance, Safety and management’ by Er. Sanjeev Mathur from Aditya Birla company. In this book he also has mentioned one section of bats above and restoration. This triggered me to write this elaborate article. Hope you will find it enjoyable and educational.

A few Basic facts about Bats :- some times people refer bats as flying mice but they are far different. There are about 1300 species of bats ranging from 6inch to a rare breed with 6feet wing size. Bats use a unique sound waves for navigation while flying hence can fly in dark nights also. Bats are the best creatures for pest control. Bats have been documented eating bugs that attack pecans, almonds, rice, cotton, corn, coffee, sugarcane, tomatoes, cucumbers, and beans. As per one of the recent surveys it was recorded that United States have saved somewhere between $3.7 and 54 billion in pest control services every year. Nectar-eating bats do this by pollinating flowers, just like bees. Anyway, there is so much to write about the facts and benefits of bats, now let’s concentrate on the engineering points.

Bad abodes:- In USA and many other developed nations a lot of study is done about the behaviors of animals towards the changing environmental conditions, construction works. In thousands of old bridges surveyed in USA and other countries more than one fourth of the bridges showed habitat of bats colonies. The first question was how to carry out the repairs with out disturbing the bats’ colonies which are very sensitive. Hence the bats restoration and preservations programs were developed which included navigation of bats to new place – repair of bridge – followed by re-inviting the bats back to original habitat (where they resided previously and used to get food in surrounding nature). During rehabilitation, the question raised as to how to make the bat abode safe for the creatures as well as the structure. For this several innovative designs of ‘Bat Abodes’ were developed by research workers which included cozy wooden planks with cross bars etc. (which could help to prevent direct sunlight / heat / vehicle sounds etc. in these abodes as well as enable the mammals to hung safe).

A few of the popular bat abode designs known are:-

1.      Texas Bat-Abode

2.      Big-eared Bat-Abode

3.      The Oregon Wedge

4.      Bat-domed Culverts

Above bat abodes were found to be successful in increasing the bat population and in preserving some of the rare breeds and thus controlling the pests and saving the food grains without use of any chemicals! Hope we do more research in India and other developing nations and preserve these mammals before they vanish from the earth like ‘dinosaurs’ vanished from earth!   

References :-

1)     Center of Environmental Excellence by AASHTO – Chapter.7 on bridge maintenance.

2)     ‘Bridge Maintenance, Safety and management’ by Er. Sanjeev Mathur from Aditya Birla company.