Autonomous Recording Units (ARUs)

Before ARUs existed, a person needed to be at the location to listen for calls. Being there in person can change how animals behave, meaning the data might not show the true story. Monitoring calls in person means that each call must be identified in the moment, and you can’t re-listen to the same call, or ask other people to check what you think the call is.

ARUs can record the calls for you, and they don’t disrupt or disturb the animals, meaning animals behave normally. 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 recorded. By using special software, species can be identified with high confidence by looking at and listening to the recorded calls many times. By having a permanent record of the calls, experts can be asked to check identifications.

Why are ARUs useful?

• 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 we 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 we 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 - abundance or density).

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.

Bird monitoring with ARUs

Birds can be monitored by using ARUs to record their calls. When setting up ARUs aiming to monitor birds, these are some things you should consider:

• Timing – monitor during times when present and calling.
• Think about seasonal changes. For example, migratory birds travel to feeding sites at certain times of year, if monitoring at these sites you would aim to
• Think about when birds are most active. Most birds are usually active during the day, with the most activity (and calling) around sunrise and sunset. However, if you are aiming to learn about nocturnal birds, then you would program ARUs to record at night.
• If you are unsure when to record, you can set ARUs to record for a short period of time, periodically throughout the day.
• Location – if interested in monitoring all possible bird species, place recorders in as many habitats that birds may be using as possible.
• Mount recorders on something sturdy 1 – 2 metres from the ground, avoiding things that might brush against the recorder (e.g. leaves or branches). Place recorders at least 250 m apart to avoid “double counting”.

Microbat monitoring with ARUs

Microbats (bats) can be monitored by using ARUs to record their calls. Bats use ultrasonic, or high frequency, calls to navigate and hunt but humans can’t hear most of these calls. Specialised ARUs with high-frequency microphones can pick up and record calls within the range that bats make them. When setting up ARUs aiming to monitor bats, these are some things you should consider:

• Habitat – choose a location where there will be bat activity, such as roosting (sleeping) sites, foraging (feeding) areas or water sources. Monitoring in places where bats are more likely to be will make it more likely that you will record them if they live there.
• 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 one might produce bad data by recording double or mixed up calls that are hard to identify.

Examples of bat call spectrograms – their calls made visible as images by computer software.

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 allows you to monitor the bat species that live in a place, telling you which bat species are present (species richness).

Frog monitoring with ARUs

Frogs can be monitored by using ARUs to record their calls. When setting up ARUs aiming to monitor frogs, these are some things you should consider:

• Timing
• Deploy ARUs at times when frogs will be calling, such as after a good rain, or during breeding season.
• Program ARUs to tell you what you want to know. Do you want to target species or do general monitoring? e.g. record at times of day when the species of interest will be calling, if you don’t know what times they will call, or if you want to know about all species, you can program to call for short periods of time distributed throughout the day.
• Location – choose sites that suit frog biology and habitat.

I want to monitor a particular species

ARUs can be used to monitor a single species that we are interested in learning more about. To learn if they live (or don’t live) in a place, we can set up recorders in ways that increase our chance of detecting the species and target their preferred habitat.

How to target species with ARUs:

• Learn about the species to help guide your monitoring.
• Where does it like to live? This can help you decide where to put the ARU.
• When does it usually call – time of year, time of day, after lots of rain, during breeding season?
• Do you know about the calls it makes? If you know what frequency range it falls within, you can program the ARU to record only calls that fall within this range.

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.