Most of us have been in the position where we’ve struggled to find something, be it your car keys, phone, or favourite pair of sunglasses. No matter how hard or long you search it just seems to elude you. One minute it’s there and the next it’s gone. You know it’s there, but where!! It’s an extremely frustrating feeling.
This feeling is all too familiar to those scientists trying to monitor one of New Zealand’s bat species, the lesser short-tailed bat. These scientists would probably argue that finding small bats in a large forest has a few more challenges than searching for your car keys at home.
To make monitoring the lesser short-tailed bat a bit easier it would be useful to know which parts of the forest they prefer to visit. Jessica Scrimgeour, Laura Molles, and Joseph Was looked into which forest structure lesser short-tailed bats are most likely to be found in. The scientists pondered over whether these elusive bats are in the forest they’re monitoring but they just can’t find them, or are they not in the forest at all.
Most lesser short-tailed bat monitoring in New Zealand has occurred at ground level. However, scientists were aware that these bats can and do fly in all levels of the forest, from way down low to way up high. Bats may be hard to find when you are repeatedly looking in the same spot in the forest.
Back in 2013 Scrimgeour (Department of Conservation), Molles (Lincoln University), and Was (University of Waikato) used automatic bat monitors (ABMs) in the North Island to investigate this. ABMs are sound activated recorders that collect bat echolocation calls. ABMs can be set at different heights in beech and podocarp forests. Generally speaking podocarp forests are made up of trees of varying heights with a thick understorey. Beech forests on the other hand are made up of different beech tree species of a similar height, with a more open understorey.
Lesser short-tailed bats prefer to fly through forests that have minimal clutter, or are the most open. ‘Clutter’ refers to, among other things, the amount of branches, leaves, and tree trunks that hinder the bats flight and echolocation.
Echolocation is the bats way of navigating. It works by bats sending out sound waves that hit surrounding objects and then bounce back to the bat allowing the bat to orientate itself. In a cluttered forest the objects are very close together, which means that the bats are still sending out sound waves at the same time sound waves are bouncing back. Returning sound waves become challenging to interpret and can interfere with tasks such as orientating and finding food.
Initially the group thought that a more cluttered forest would attract more bats, as clutter might mean an increase in biodiversity, with better quality food available. Even if the cluttered forest had the most food, which for bats is insects, they preferred to take the path of least resistance. Navigating through dense forest is just hard yakka, requiring too much energy. No surprises there, who doesn’t take the path of least resistance?
Lesser short-tailed bats are very committed to taking the path of least resistance and even change the height they fly at depending on the type of forest they’re in. In the beech forest, bats spent the most time flying in the bottom tier of the forest, as this part was the least cluttered. In podocarp forest, bats spent most of their time flying in the least cluttered middle tier of the forest.
As New Zealander’s we like to think that we are different to the Aussies across the ditch, but our bat species don’t quite think the same. The trans-Tasman bats are actually very similar to each other. Other research on bats in Tasmania found that bat flying activity is greater when the forest is more open. So I suppose you could say that the Tasmanian bats are a bit lazy like our bats, or they behave optimally!
The results from this 2013 study have also been backed up in subsequent research in New Zealand. This research found that in urban and rural settings long-tailed bat activity was also effected by vertical airspace and horizontal microhabitats.
For those on the lookout for bats this study has helped with deciding where to place monitoring devices for more robust monitoring programmes. Finding that needle in the haystack has just a little bit easier.
What’s been happening with monitoring programmes for bats since 2013? Well, it turns out quite a lot. Acoustic monitors are now used instead of ABM’s. These monitors are basically microphones that record bat echolocation calls as they fly past the monitors. More research has gone into where bat activity is likely to be the highest to further help in the placement of acoustic monitors.
This new knowledge has definitely paid off with the exciting recent discovery of a population of the lesser short-tailed bats in the lower North Island. It was thought that the lesser short-tailed bat was extinct from the Pākuratahi forest, Upper Hutt, because bats had not been detected there for a very long time. It just goes to show that just because you haven’t detected something doesn’t mean it’s not there. Sometimes you just need to look a bit harder or, at least, a bit smarter.
Scrimgeour, J. Molles, L., & Waas, J. R. (2013). Vertical variation in flight activity of the lesser short-tailed bat in podocarp and beech forest, Central North Island, New Zealand. https://researchcommons.waikato.ac.nz/server/api/core/bitstreams/fe6c95f0-a86d-408b-a6b4-cbc112a24865/content
This article was prepared by Postgraduate Diploma in Applied Science student Anna Gardiner as part of the ECOL608 Research Methods in Ecology course.
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