Biology 342 Fall 2015
Nathaniel Klein and Sophia McKean
The phylogeny of a behavior is how the behavior has come about through a species’ evolution. This is different from Ontology, which focuses on changes in behavior within an organism's lifetime. If animals have the mechanistic capacity for a behavior and that behavior increases its lifetime reproductive fitness, it is likely that the behavior will be favored by evolution and become prevelant in a population or species. In corvids, calling behaviors have evolved in response to the fact that corvids are a generally large, social, monomorphic birds that live in a wide variety of environments, and having complex vocalizations can therefore be highly advantageous. For example, in most species of birds body size is proportional to the pitch of their calls. Corvids tend to be rather large, and thus most have low pitched calls, but some large forest dwelling corvids have evolved higher, more tonal calls. This adaptation allows their calls to travel further in the acoustic environment of a forest than the guttural caws of most corvids (Lailo & Rolando 2003). The vocalizations of corvids have evolved to work in their environments, and have also helped them evolve into many environments.
Most species of Corvids are also highly social, and monogamous. Some form family groups in which the young remain around nests for a few years before going off and finding mates. This makes it very important for them to be able to tell apart not only different sexes, but also the identity of specific individuals. Vocalizations are an effective mechanism for communicating information about identity, because Corvids tend to look similar to each other and this calling allows them broadcast information over greater distances (Mates et al. 2015). Vocalization also has enabled corvids to evolve into a highly social species. Some species are able to communicate information about dominance hierarchies through various mechanisms (Kondo & Hiraiwa-Hasegawa 2015), and have different types of calls for different situations (predator alarms, feeding, etc.) (Mates et al. 2015). These calls are often specific to a given social group, but share basic acoustic properties that are linked to their meaning.
The meaning and vocalization of these calls are learned by Corvid chicks from observation. Corvids and other song-learning birds have two different parts of their brain that allow them to imitate, learn, and reproduce calls that they hear. The ability to learn vocal information is similar to humans’ ability to learn to speak; corvids and humans have evolved similar neural pathways. This is most likely a case of convergent evolution, because humans and vocal learning birds didn’t inherit these abilities from a recent common ancestor (Pfenning et al. 2015a).
Figure 1. This figure was taken from a paper comparing how anatomically similar humans and songbirds’ brains are (as both humans and songbirds are vocal learners.) The has different song control nuclei labelled, with the various brain regions that each nucleus resides in illustrated with different colors. It also shows how each nucleus signals to another and which regions in the songbird versus human brains are similar (Pfenning 2014).