Mountain chickadee chatter: Scientists are decoding the songbird’s complex calls

Members of the Pravosudov lab catch and release resident chickadees to attach identifying bands that allow the researchers to track individual birds.(Sofia Haley)

I spend my days out at our field site in the beautiful Sierra Nevada, following and recording chickadees as they communicate with each other. I have taken numerous focal recordings, where I stand in the forest with a directional microphone, identifying vocalizations and behaviors in real time.

I also have hundreds of hours of recordings taken by automated recording devices called AudioMoths. These allow me to record vocalizations in the absence of people.

The extensive vocal repertoire of mountain chickadees has yet to be fully documented. There are five basic categories of call types:

• Contact calls: communicate identity, sort of like a name, and location.
• “Chick-a-dee” calls: coordinate flock movement and communicate a variety of complex information about the environment, from food availability to predator presence and type.
• Alarm calls: alert others of the presence of a predator.
• Begging calls: used by chicks or females to elicit feeding behavior from males.
• Gargle calls: advertise dominance over other individuals in a flock, primarily used by males.

“Chick-a-dee” calls contain several elements resembling the basic elements of human grammar. Essentially, the various sounds a chickadee utters mean different things, similar to words in human languages. And the way that a chickadee combines these sounds changes the meaning. Word order matters, just like grammar matters in human language. If a chickadee were to phrase its calls in the wrong note order, the call would no longer convey the same meaning, even if composed of the same elements.

The “chick-a-dee” call of the mountain chickadee contains six elements, known as notes or syllables, that can be combined in hundreds of unique combinations to say many different things. These elements are labeled A, A/B, B, C, D and Dh.

Although scientists don’t fully know the meaning of each note in different contexts, it is generally believed that A notes typically contain identifying information about how important the topic seems to the caller, while A/B and B notes tend to further inform the listener of the topic of conversation. C notes contain information about the subject of the call, often a food source, and D notes convey information about the excitement and urgency of the message, including level of threat of a spotted predator or size of a food source. The D notes basically function like exclamation points at the end of a sentence, while the other notes convey more specific information.

Mountain chickadees can use their “chick-a-dee” calls to convey hundreds of different phrases that are relevant to navigating their habitats and social environments. As a hypothetical example, a mountain chickadee call might have the following syntax: A-A-A/B-B-D-D, which could roughly translate to something like, “Listen to me carefully (A-A): there is a predator (A/B) close by (B) and a medium threat level (DD).”

If the note order switched to D-A-B-D-A/B-A, the sentence would look more like: “Noteworthy listen close by noteworthy predator listen to me.” Although all the same elements are there, this sentence is now much more difficult to comprehend. Notes that are out of order can confuse chickadees, preventing them from grasping the correct meaning of the call.

This “translation” is an example based on what we have learned from playback experiments, but the exact meaning will depend on the specific population and surrounding environment.

Analyzing the ‘chick-a-dee’ calls

Back in the lab, I parse through the endless hours of recordings using a deep-learning algorithm that I have modified to identify the specific calls of our chickadee population.

I then use Raven Pro software, developed by the Cornell Lab of Ornithology, to visually inspect and analyze these calls on a spectrogram: a visual representation of sound, with frequency on the vertical axis, and time on the horizontal axis. This visualization allows me to study the structure of calls in great detail.

Studying spectrograms can get me only so far. The next step is to experimentally test different “chick-a-dee” calls out in the wild. Using audio editing software, I manipulate the syntax of calls to either follow grammatical rules or violate them. Then, I broadcast these manipulated recordings out in the forest and observe how our chickadees react to grammatically incorrect calls, which would sound like gibberish to them.

My hope is that this combination of experimental testing of calls and careful visual analysis will provide a step toward understanding the subtle complexities of chickadee communication. I’m trying to home in on the meaning of different syllables and syntax, the grammatical rules.

Back in the forest with my directional microphone, watching the chickadees flit about, I hear different versions of the “chick-a-dee” calls. Some feature more D notes, which would indicate a higher level of excitement. Others feature more A, B or C notes, communicating more specific, identifying information. I am also surrounded by melodic gargle calls, harsh scolding calls and barely audible soft calls.

Next time you find yourself out in the forest, stop and listen to the chickadees as they talk to each other. Maybe you’ll be able to hear the variation in their calls and know that they are talking about different things − and that grammar matters.

This article is republished from The Conversation under a Creative Commons license. Read the original article.