“Singing bird on Ilkley Moor” By Tim Green CC 2.0
What is Vocal Mimicry?
Mimicry is characterized as a resemblance of two or more organisms that are not closely related taxonomically. In mimicry, two or more different organisms emit near identical signals that have at least one common receiver. The receiver reacts with the same response to both stimuli because in one of the cases it is advantageous for its survival but in the other case, it is disadvantageous. There are multiple variations of mimicry, but vocal mimicry is most commonly a form of Batesian mimicry, where a harmless organism mimics a warning signal by that organisms predator causing the individual’s natural instincts to kick in and flee the scene (see caterpillar video below). Vocal mimicry can be performed for many other uses which include mating and hunting which creates different advantages for the individuals.
Adoptions of Vocal Mimicry
As far as vocal mimicry goes in non-human animals, the most common occurrence is found in different species of birds. It was estimated that between 15% and 20% of passerine species (which make up more than half of all species of birds) use some sort of vocal mimicry in their songs that are adopted from other bird species. One heavy divulger in vocal mimicry is the species Acrocephalus palustris, commonly known as the marsh warbler, which adopts imitations from 99 different bird species in Europe and over 100 Eastern African species including 33 non-passerines, but each individual averages about 75 different imitations. Marsh warblers are born in Europe but are still young enough to adopt new musical tones when they fly south during winter. While there’s no stand-alone reason the marsh warbler imitates so many birds it may just be a method in which the individual embellishes their song.
Another bird which adopted the use of vocal mimicry is the fork-tailed drongo (Dicrurus macrocercus). The drongo uses vocal mimicry to assist in feeding through the form of scavenging known as kleptoparasitism, which is the act of stealing food from a different organism that collected it. Drongos have the ability to imitate the warning signal of the sentry. The sentry is the standing meerkat on guard looking for predators, and if one is spotted, the sentry barks and the entire group of foraging meerkats drop what they have and dash to one of the holes in the area for protection. As can be seen in the video above, the drongo overwatches a group of meerkats and waits for one of the scavenging meerkats to capture a meal before it imitates the bark of the sentry. The foraging meerkats disperse and the drongo gets the food with little effort used. Vocal mimicry like this is very advantageous but is something we rarely see and this is because of how uncommon the gene for vocal learning is known as FOXP2.
Forkhead box protein P2, also known as FoxP2, is a protein that is a result of the FoxP2 gene which resides in a number of vertebrates. FoxP2 plays a large role in communication and is often referred to as the language gene because a mutation in the gene often results in speech disorders in humans. Vertebrates such as alligators, mice, whales, dolphins, and many songbirds posses the FoxP2 gene or at least some variation of it, and while other birds have a similar sequence of the protein, not all are able to learn songs (sorry chickens).
“Distribution of song learning among birds” (left) “Amino acid sequences of FoxP2 exon 7. Dots represent amino acids identical to sequence” (right) By D.M. Webb and J. Zhang
The FoxP2 protein is a heavily conserved protein appearing in the 95th percentile of most conserved proteins which shows the importance of communication evolutionarily. Between humans and mice there are only three differences in amino acid sequence, and between humans and chimpanzees, there is only a change in 2 amino acids. These changes could, however, result in a change in the secondary structure of the protein in humans, as the changes allow for phosphorylation by protein kinase C. These changes in the human sequence likely happened recently as no other lineage includes these sequence alterations, but as we’ve seen, these changes aren’t needed to perform successful mimicry, just ask the drongo.