What Are Acoustic Fingerprints?
Just as your fingerprint is unique to you, acoustic fingerprints are unique in time and space, reflecting the sounds within an environment at a specific point in time. Every location throughout the day and across seasons will have a different acoustic fingerprint because sounds are constantly changing. These unique images are made by recording sounds of the natural world across 24 hours and transforming the data into images called Long Distance False Colour Spectrograms. They visually represent sound with time along the x-axis (along the bottom) and frequency, the pitch of the animal call, along the y-axis (the left side). The colours you see on the black background represent different animal calls. Every sound produced in the world has a different duration, frequency, energy level, complexity and decibel level and it is these properties that determine the colours and shapes you see here. When an animal calls several times in the audio recording, it leaves a coloured mark on the spectrogram. The more colour, the more species and individuals that are calling, therefore the more biodiversity that exists. Some animals are so unique in their calling pattern they leave easily identifiable colours and shapes. Some of these have been identified on the image.
What am I Looking at?
Let’s look at an example of an Acoustic Fingerprint from Costa Rica. The image starts at 05:00 where you can see the intense activity of the “dawn chorus”. It then quietens down as the temperature increases and the animals rest. We see another peak in activity later in the afternoon, known as the “dusk chorus”, where the animals are active once again as the temperature cools. During the day you can see lots of reds, pinks and purples between 6000-7000 Hz (frequency); these are the sounds of stridulating insects such as cicadas. These insects increase the frequency of their calls with the temperature. So in the morning, when it’s colder, you can see they call at a lower frequency. At night we see a complete shift in activity. Other species of insects start calling at a similar frequency, but with a simpler call pattern, indicated by the blue colours. Between 2000-5000 Hz we can also see the chorus of the frogs, with many species calling at the same time but across different frequencies.
What do the Colours Mean?
Red Species that call continuously with a complex call pattern containing different levels of energy and decibel levels, such as birds and crickets.
Green Species that call in short bursts with a high amplitude (loudness); a strong, concentrated and sharp sound.
Blue Species that call continuously, but unlike with red colours, the calls are much less complex.
Pink and Purple Both complex (red) and basic (blue) continuous calls are occurring at the same time.
Cyan Short and strong calls (green) and continuous basic sounds (blue) occurring at the same time.
Orange , Yellow and White These colours indicate sounds from all types of call together.