A comparison between bird monitoring techniques
Earlier this year one of our open source contributors, Sara Coutinho completed her Lincoln University research project comparing traditional bird counts and audio recording systems for estimating bird richness. Sara compared the number of birds species detected by a novice and an expert doing 5 minute bird counts the number of species detected by two audio recorders: the DOC AR4 and the 2040 bird monitor.
Interestingly there was no significant difference between the the number of species detected by the novice, experts and the DOC recorder.
When comparing the DOC AR4 to the 2040 bird monitor, the 2040 bird monitor detected about 35% less bird species. This might be because the 2040 bird monitor has a less sensitive microphone with a smaller detection range. If the bird species were distributed evenly in the space around the microphones then the 2040 recorder covers 1-35% or 65% of the volume of the DOC AR4. Our (2040, not Sara) back of the napkin estimate of its relative range is the cube root of that, or about 86% of the DOC AR4 (calculating the range accurately could easily be another study).
You can watch Sara's video presentation below or read her report on comparing methods for estimating bird richness.
Why use the 2040 bird monitor?
The 2040 bird monitor has a smaller range than the DOC AR4 - so why would you use it?
Ease of use
The first reason is that the 2040 Bird Monitor is easier to use because the recordings are uploaded to the cloud where they can easily be processed and listened to. The recordings also automatically have the GPS coordinates associated with each recording making it less likely that you'll make mistakes.
With the solar panel option the 2040 Bird Recorder can be permanent installation. This means for a very low cost (because no labour is required) you can monitor birds all year round. You can measure how the change through the seasons and from year to year. The longevity somewhat makes up for the lack of range. A bird only needs to come within range of the recorder while it is recording for it to be detected. This means that you can detect birds that are only in the area for part of the year.
Automatic recording devices also have the benefit of recording at night time, whereas human 5 minute bird counts tend to be during the day.
The other major advantage of the 2040 Bird Monitor is that the recordings uploaded to the cloud are processed and stored so future algorithms can be applied to them. At the moment a Cacophony Index is calculated that measures the amount of bird song. There is also a very early version of an automatic bird recognition algorithm being applied to each recording. We will examine this in more detail in another blog post (the summary is that there is lots of room for improvement, but we are actively working to make a better version).
Our conclusion from Sara's study is that you need to chose the right tool for the job and understand the capabilities and limitations of the different tools. If you want to measure bird species richness over a short period of time - then the AR4 will give you the best results. If you want to measure over a longer period of time the the 2040 Bird Monitor is a lot more cost effective and should be the best tool for the job.
We would like to thank Sara for her work allowing us to publish her results on this blog.