Farmscape Wonder Wander: 14 August 2020

By Stephanie

One of the projects I have been working on with the help of Jill Jakimetz is creating sound maps of the Bobolinks here on the farm. Sound maps display the power of sounds over a landscape. They show us where the sound is coming from as if we were standing in that landscape. To create these sound maps, we set up recorders to capture the Bobolink’s calls and collected 456 recordings equaling to 912 minutes of sound all over a period of 24-hours.

I’m sure many of you are familiar with the Bobolink. Starting my internship here was the first I had heard of them. The males are easily distinguished by their coloration because of their white backs, the yellow patch on their head and black underparts. When I first saw them fly, it almost looked like they were flying upside down since I’m so used to the opposite coloration! The females are a warm brown in color with streaking on their flanks.
Bobolinks are grassland birds that are highly associated with agriculture as they nest in fields and pastures. Boblinks have been in decline for years due to habitat destruction because farms have been mowing their fields earlier and earlier. Many farms are now starting to delay their mowing till the Bobolinks migrate to allow for them to nest and breed. At the end of the summer, the Bobolinks fly south all the way down to South America to overwinter there.

The field we chose to study is Big Hill due to it being left un-mowed until August. This allows for the Boblinks to thrive in the undisturbed tall grass. We spread out 19 recorders by 100 feet in a grid. They only covered a quarter of the field. If we had spread out the recorders to cover the entire field, the sound maps would be more generalized and not catch the more detailed nuances.

Here is the setup of the recorders. The recorder is attached to a pole about a foot off the ground. The box contains the battery and hardware for the recorder. The recorders are set up to record 2 minutes per hour for 24 hours.

To analyze the recordings, I used the program Raven. This is what a Bobolink’s call looks like on a spectrogram. A spectrogram is a visual way of representing the loudness or signal strength of a signal over time at various frequencies. Bobolinks have very distinct calls. To me they sound like a modge-podge of random notes mushed together or, as a Star Wars fan, it sounds like R2-D2. But after listening to it over and over again, it starts to sound like a beautiful song. The ornithologist, Arthur Cleveland Bent, described the Bobolink’s call as “a bubbling delirium of ecstatic music the flows from the gifted throat of the bird like sparkling champagne.”

After analyzing the recordings, I created sound maps using the program ArcMap. Here are the maps from 10am to 5pm on June 17th. The highest number of calls recorded was 20, shown in red and the lowest was zero, shown in blue.

Here are the sound maps from 6pm to 8pm on June 17th and 5am to 9am on June 18th. After the recording at 8pm, the Bobolinks stopped calling. The recording picked them up again starting at 5am.

This map shows the totals of the Bobolink calls over the whole 24-hour period. It seems as though the Bobolinks were most active towards the center of the field, or the bottom right edge of the grid. The highest number of calls was 189 and the lowest was 110. It’s hard to get an accurate number of active Bobolinks from this data, since the recordings are only for 2 minutes per hour and Bobolinks can call multiple times during that time. But from my observations out in the field, there were plenty of male and female Bobolinks flying around and nesting in the tall grass.

So, what’s next? I plan on doing another 24-hour recording next week now that the field has been mowed. I’ll be focusing on the singing insects that are in the field rather than the Bobolinks since they have all migrated south. It will be interesting to see if there are any similarities between the sound maps. Stay tuned!