When scientists study questions of mechanism, they study how animals are able to engage in a behavior. This means understanding how animals’ physiology and neural or hormonal pathways enable the behavior. In the case of corvid vocalization, this means exploring which neural connections in their brain allow them to produce and learn song, what kinds of vocalizations they are able to make, and how much variation they are able to recognize within conspecific calls. If crows were unable to produce and learn complex vocalizations, or if they could produce these but were unable to get much information from other corvids' songs, this behavior would not be as important to corvids. Understanding the basic mechanisms behind corvid vocalizations lays the foundation for understanding how and why this behavior might have evolved, understanding how it increases their lifetime fitness, and understanding how they are able to learn it.

There are two distinct types of corvid vocalizations. The first is usually referred to as a “ka” or a “contact call”; this call is a single note, either repeated or not. The other type of vocalization is often called a “sequential call.” These consist of multiple notes, so corvid species often have a large amount of sequential calls. For example, large billed crows have at least twenty documented different sequential calls (Kondo 2015). A study of jungle crows found that they were able to distinguish between different crows merely by hearing each crow’s ka. Each crow’s ka has distinct frequency features (see Figure 1), such as different minimums and maximums (Kondo 2010). It has also been found in ravens that though all individuals are able to make about the same number of sequential vocalizations, non-dominant ravens suppress this ability, actually vocalizing only a few of these, while dominant ravens vocalize all of their potential calls (Heinrich 1991).


Figure 1. This figure was taken from a paper which showed how jungle crows can recognize one another based on their “ka” calls. Above are the frequencies of five different crows’ kas. These show how each crow’s ka frequency has distinct characteristics (Kondo 2010).

Much is also known about the neural mechanisms that allow corvids to produce and learn vocalizations. Large billed crows have several song control nuclei (SCN), which are divided into two main pathways. The first pathway is called the “motor pathway” and is what allows crows to actually sing. The second pathway is called the “anterior forebrain pathway” and is what allows them to learn and recognize songs. Both of these pathways involve multiple song control nuclei signalling to each other. Some of the most important nuclei are the HVC (which is involved in both pathways), Area X (anterior forebrain pathway), and the arcopallium (RA) (which is also involved in both pathways) (Wang 2009). These pathways and SCNs described for the large billed crows can be generalized to other corvids, and song-learning birds in general (Pfenning 2014). For a figure illustrating which SCNs signal to which and how these pathways compare to similar pathways involved in human vocalization, see Figure 1 on the Phylogeny page.