“Singing bird on Ilkley Moor” By Tim Green CC 2.0
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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.
“This caterpillar mimics the alarm calls of its predators” By ScienceMag
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.
“Drongo Bird Tricks Meerkats” By BBC Earth
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.
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.
This is very informative and I learned quite a lot from this article. I really enjoyed reading about the warblers embellishing their songs and the drongo bird’s mimicry to steal food from the meercats. This relates a lot to what we discussed in class today about communication in animal communities.
Fascinating story of the drongo and meerkats! Is this an example of sensory exploitation or signal deception? Explain. Think about costs and benefits to both signalers and receivers. If fitness costs were high and persistent enough for the meerkats, what might you predict would happen over evolutionary time to the sentry calling behavior?
I would think this leans more towards signal deception because sensory explotation acts on pre existing sensory abilities of meerkats. I doubt, but I could be wrong, meerkats are born knowing that a bark means a predator is near as I would think they would follow the lead of other meerkats in their early stages. Signal deception would seem to work because the bark is just an alarm to run which could alter from meerkat population to meerkat population. If the drongo was such an issue for the meerkats, sentries that could be immitated by drongos would be wiped out as well as the population they live in while populations that can’t be mimiced live on, these populations that live on could have sentries with bark tones that the drongo is physically unable to mimic making their immitations useless.
I really learned a lot from this article. I really enjoyed the videos you posted as they reiterated everything you said. I especially liked your use of the FoxP2 protein phylogenetic tree as it helps to illustrate the distribution of song learning among birds.
Josh-
I couldn’t help but think before reading this about a parrot I came across that would always mimic when somebody coughed. It had the exact pitch of a human cough and I found this to be so interesting. After reading your post I now know that many other animals do this as well. Who knew caterpillars even made sounds? I also came across reading about the FoxP2 gene researching for my blog post about dolphin communication. I know you mentioned about a mutation in this gene causes humans to have a speech disorder, what happens when this gene is mutated in a vocal animal? Do they have trouble communicating? Great Post!
I couldn’t find anything about birds with mutations in the FoxP2 gene, I think they’d be a little difficult to locate. I did however find a paper on mice with mutated FoxP2 genes which were induced via recombination in embryonic stem cells. The gene was modified to match the human form of the FoxP2 gene and there was another mutation known as the knock out version of FoxP2. The mice with the human version of the gene had no differences compared to mice with the “mouse version” of the gene. The mice who had the knock out version of the gene died within 3 or 4 weeks, so there is a lot that can happen with modifications to the gene. My guess is with the right amino acids modified a bird could certainly have difficulties mimicing song. https://doi.org/10.1016/j.cell.2009.03.041 <- Here's the paper on the mice if you want to check it out!