Monday, March 7, 2016

The Call of the Pika

Some of the most interesting places for pika researchers to study pika are at the edges of suitable pika habitat - places where conditions often aren't ideal and if there are any pika there probably won't be many. Discovering pika at such locations can be time intensive and even with a lot of time spent, it is still possible to miss an animal that is there. The initial goal of the pika audio project is to be able to help with situations like that. If successful, it will be possible for a researcher to leave a recording device in the field for days at a time and then use our program to automatically analyze the audio and identify pika calls that may be present. It would still not be a guarantee of finding pika that are there, but it could be a good option to increase monitoring coverage without significantly increasing human-hours.

With that in mind, our goal is to be able to efficiently analyze large quantities of audio to find pika calls. How do we do that? Let's start out by looking at what a pika call looks like. A spectrogram is a common tool for examining audio graphically by providing a way of looking at the strength of different pitches in an audio signal. Here is a spectrogram (also called a sonogram) of a pika call:

Audio of the pika call:
For this pika call there are four main pitch bands (along with a few bands of lesser intensity) that appear to be fairly evenly spaced from each other throughout the short call.
For comparison, here is the spectrogram of a song sparrow song:

(thanks to Matt Goff for the song sparrow audio)
Audio of the song sparrow song:

Although the different time scales in each of the above spectrograms make them a little tricky to directly compare, it is possible to see that the pika spectrogram is distinguishable from the song sparrow spectrogram. In my next post I will go into some of the details of how we use some of the features of the pika call spectrogram to pull their calls out of a larger audio file.