Shifting the focus of agri-environment schemes: managing for bats around farms

A freetail bat (Mormopterus sp.) which we trapped so we could build a key of the local dialect.

Bats are fascinating creatures – there are about 1,200 species, and they are the second most abundant mammal (behind the rodents). They occupy every continent aside from Antarctica, and are the only mammal capable of true flight.

In spite of their incredible diversity and abundance, there is still much we don’t know about bat ecology and management: they are quite cryptic which can make them tricky to study!  I had the opportunity to carry out some research on bats in agricultural areas as part of my PhD, the findings of this which have just been published in PLoS ONE (which you can find here and download for free). Here’s a summary of what we did, what we found, and some of the other details that get lost in the scientific publication process.

Why bats in agricultural areas? Well for a couple of very important reasons. Bats are relatively hardy little creatures, and often make up a large proportion of the mammalian fauna in agricultural areas when other species have become locally extinct. As insectivores, they provide a vital ecosystem service to farms by controlling insect pests, and consume 40-100% of their body weight in a single night.

The difference between land sparing and wildlife friendly farming.
Image: Phalan et al (2011), Food Policy 36, S62

Also, there is ongoing disagreement as to how we should be managing farming landscapes to balance food production and conservation. Is it better to segregate large fields of intensive production from conservation areas, or have lower-input system which integrate the two? The so-called “wildlife-friendly farming vs. land sparing” debate has primarily focussed on what is best for plant and bird species, but evidence for bats remains inconclusive. Given their role in controlling pests, I thought they warranted more attention.

Finally, I was concerned with the potential loss of travelling stock routes (which was the focus of my PhD research). Originally used for moving stock, stock routes now form large wooded corridors in the fertile flat portions of otherwise heavily cleared eastern Australian farming landscapes. Bats require old trees with hollows for roosting and breeding, and access to water. So although we strongly suspected that stock routes would form important habitat for bats, we wanted to quantify this.

The aim of this research was to answer a couple of questions:

1)      Are travelling stock routes providing important habitat for bats in the highly fragmented wheat-sheep belt?

2)    Is there evidence that bats will benefit from schemes designed to make the landscape more “friendly” to wildlife?

A bat detector on a large remnant tree in a heavily grazed exotic pasture. The wooded stock route can be seen in the background.

Now, bats use echolocation to locate their prey, and their calls are ultrasonic so we can’t hear them. Each bat species produces a slightly different type of call, so automated keys can be used to count the number of species flying past a “bat detector”. The only problem is that there are regional differences in these calls, sort of like the dialects of a language. Because we weren’t fully confident that we had an adequate grasp on the bat dialect of the slopes region I was working in, we set out to collect more calls. With the help of a couple of seasoned bat researchers, Caragh Threlfall and Anna McConville, we managed to trap nine species from our study area and collect local reference calls.

Armed with our regionally-specific key, we then set up bat detectors in travelling stock routes, as well as paddocks which represented all the common land uses in the area: native and exotic pastures, and lucerne, wheat and canola crops.

A bumper crop of insects in the UV light trap.

We also set out black-light traps to determine whether differences in bat activity between paddocks could be driven by the amount of insects active each night. Field work during the summer of 2010/2011 was made all the more fun by the La Niña conditions which brought drought-breaking rains, and associated shutting of roads, bogging of the field vehicle, and bumper collections of insects in the light traps.

It might look like just a weathered old tree in a paddock, but we recorded over 500 calls and 10 species around this Bimble box (Eucalyptus populnea) in a single night!

During this process I had many an interesting conversation with landholders, who were keen to know what I was investigating, and why I was stomping around their paddocks with buckets, lead batteries, plastic boxes and UV lights. After explaining the aims of the project, some were sceptical about whether I would record any bats at all (including the owner of the tree on the right) because they didn’t think that they occurred in the area. This just goes to show that in spite of their great numbers, bats and the services they provide still often go overlooked because of their nocturnal nature and inaudible calls.

Over 228 detector nights and 2,475 survey hours, we recorded 91,969 bat calls representing 13 taxa. We also collected 5.14 kg of dried insects. The data told us that all of the land uses supported the same amount of insects yet:

  • There was higher bat activity in stock routes, and more bat species in wider stock routes;
  • There were more trees characteristic of bat roosts in the stock routes;
  • There were more bat species, and higher bat activity in the native pastures, the lowest-intensity form of farming; and
  • There was also more species and activity in paddocks with retained habitat structures such as trees and logs.

This just goes to show that potentially economically important groups such as bats can benefit from low-intensity farming and agri-environment schemes, and that the retention of existing wooded areas such as travelling stock routes should be encouraged. I hope I’ve also convinced you that bats are worthy of your attention: want to learn more? Check out the Australasian Bat Society or Bat Conservation International.

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