Monitoring Country
Autonomous Recording Units (ARUs)
Autonomous Recording Units (ARUs) are a useful tool for monitoring animals that make calls or songs, like frogs and birds. They are a sound recording device that can be set to automatically record the sounds of Country over time and save them to a memory card.
Before ARUs were used to monitor animal calls, a person needed to be at the location to listen for calls. The presence of the person monitoring might change the behaviour of the animals, which could mean that the data might not be showing the true story. Monitoring calls this way also needs each call to be identified as they are heard, and you can’t re-listen to a call, or ask somebody else to check the identifications you make.
ARUs can record the calls for you, with the benefit of causing less disturbance to the animals you want to learn about. You can set the ARUs to start recording any time a call is made, or to record at specific times. For example, at night for bats, or after sunset and before sunrise for night parrots. Then, you can check the sound recordings using computer software to see which species’ calls have been captured. By using specialised software, species can be identified by looking at or listening to the recorded calls. By having a permanent record of the calls, experts can be asked to check identifications.
Song Meter. Credit: Department of Energy, Environment, and Climate Action.
- Less stress for animals: Animals often change their behaviour when people are around.
- Hear what we miss: ARUs can record all day and night, recording sounds made by animals that don’t call much or those that call when we're not around.
- Do the time for you: ARUs can capture data for long periods of time, requiring less time on Country. Monitoring over longer periods of time can increase the likelihood of picking up rare species, or species that don't call often. But they can need lots of time in the office to manage and analyse data.
- Listen again later: Unlike relying on memory, ARUs save all their recordings. We can listen back later and use special computer programs to figure out which animals made the sounds.
What can ARU's monitor?
ARUs can monitor the species calling on Country, like frogs, birds and bats, and some vocal mammals like Koalas and Gliders.
What can you learn?
- Biodiversity – what calling species live on Country
- Species Richness – how many different calling species live on Country
- Habitat preferences – what habitats species like to use and when they use it
If you monitor at the same place at the same time every year, you can see if there are changes to the species that live on Country. You can look at changes over time and decide if your management, like Feral Cat control, is working well.
What can’t you learn?
You can’t monitor animals that don’t call or aren’t calling at the time when you are monitoring. You also can’t assume that because you didn’t hear a species calling, that it isn’t on Country. Maybe it just wasn't at the sites where your ARUs were, or it only calls at specific times of day, night, or year.
You can’t find out the number of animals living on Country (population size).
Using ARUs the Right-way
ARUs produce A LOT of data! Depending on how many devices are put out, their settings, and how long they are out for, ARUs can record hundreds to thousands of hours of audio data, which you then need to process (listen to!). Think about how you will process and manage the data:
- Make sure it is well organised (labelled, in logical folders) so that people can find data when they need to.
- Make sure that data doesn’t get lost or corrupted; and if this happens, is recovery possible, or are back-ups available.
- How and when will you listen to all of the recordings? Do you have the time? Can it be shared with other people?
The way we use ARUs to monitor should be tailored to what we are trying to monitor.
Interfering sounds:
- Mount recorders on something sturdy 1 – 2 metres from the ground, avoiding things that might brush against the recorder (like leaves or branches).
- For birds, place recorders at least 250 m apart to avoid “double counting” (recording the same call on more than one device).
- For bats, make sure that the ARU microphone is not aimed towards a solid surface like a big tree or rock face. Bat calls bounce off surfaces like this, so an ARU microphone aimed towards a solid surface might record double or mixed-up calls that are hard to identify.
Animal specific: You will need to decide if you want to monitor lots of different species or target one species.
Bats use ultrasonic, or high frequency, calls so you will need to use specialised ARUs with high-frequency microphones to pick up and record calls within the range that bats make them.
Timing:
- Choose the ARU settings to only monitor when your target species are calling. Find out when those species are most active – for example, frogs are most likely to be calling during their breeding season, but this can be different for different frog species.
- Consider seasonal changes – for example, if you are interested in migratory birds, find out at what times of year they travel to feeding sites at certain times of year.
- If you are unsure when to record, set the ARUs to record for a short period of time at regular points through the day and night.
Location: If you are interested in monitoring lots of different species, place ARUs in as many habitats that those species may be using. If you are only interested in one species, place ARUs in their preferred habitats.
Monitoring a specific calling species with ARUs
ARUs can be used to monitor a calling species that you are interested in learning more about. To learn if they live (or don’t live) in an area, you can set up ARUs in ways that increase the chance of detecting the species by targeting their preferred habitat. By learning the following you, you can adapt this method to the target species:
- Where does it like to live?
- When does it usually call?
- What calls does it make, including the frequency?
Using this information, you can adapt the Environmental Monitoring Method: Biodiversity Monitoring with Autonomous Recording Units (ARUs)
Bird monitoring with ARUs
ARUs can be used to monitor one or more species of calling birds living on Country. Most birds are active during the day and ARUs should be programmed when they are most active at sunrise and sunset. But if you are interested in nocturnal birds, the ARU should be programmed to record at night.
You can learn more on the Birds page and in the Environmental Monitoring Method: Biodiversity Monitoring with Autonomous Recording Units (ARUs)
Microbat monitoring with ARUs
ARUs can be used to monitor one or more species of microbats living on Country. You will need to use specialised ARUs that have high-frequency microphones that can pick up their ultrasonic calls.
Each bat species has unique calls, so the recordings can be analysed using specialised software that makes the calls visible as pictures, called spectrograms. By looking at the spectrograms, you can identify which bat species made the recorded calls. This method tells you which bat species are present (species richness).
You can learn more on the Bats page and in the Environmental Monitoring Method: Bat Monitoring with Autonomous Recording Units (ARUs)
Frog monitoring with ARUs
ARUs can be used to monitor one or more species of frogs living on Country. Frogs are usually call after good rain and during breeding season. You will need to adapt the timing of your survey depending on where you are and what species of frog you have on Country.
You can learn more on the Frogs page and in the Environmental Monitoring Method: Biodiversity Monitoring with Autonomous Recording Units (ARUs)
Soundscapes
There is work being done to understand what healthy Country sounds like. This is called “Soundscapes”. If you would like to use this method, we recommend that you talk to an expert.
Any time you do work that might disturb or interfere with native animals and vegetation, particularly threatened species, you need to check with the state authorities to see if you need any approvals, such as scientific licences or animal ethics committee permits.
Primary sources
This landing page was developed using the following sources:
This landing page was developing using the following sources:
- Bird Survey & Assessment Steering Group: Acoustic survey methods | Bird Survey Guidelines
- Department of the Environment, Water, Heritage and the Arts: Survey guidelines for Australia’s threatened bats
Tools and Resources
Examples of acoustic analysis software:
- Kaleidoscope: the free version has a spectrogram viewer that allows you to listen, view and label audio recording. The paid version has more functions.
- Raven: the free version lets you record, save and visualize sounds as spectrograms and waveforms. The paid version has more functions.
- WarbleR: you can use open-source bird recordings or enter your own data for visualising in spectrograms
- Arbimon: free online acoustic analysis platform that allows you to upload, store and analyse data.
Online libraries of wildlife sounds:
- Xeno-canto: an online collection of wildlife sound recordings
- eBird: an online collection of bird sound recordings
- Bat calls of New South Wales: a region-based guide to the echolocation calls of Microchiropteran bats
EMSA standardised survey methods: Vertebrate Fauna Module.
Webpage version: CM-GA-JH-GA-250526