Southeast asian bird species converge on similar appearance in flocks

A recent study published in Philosophical Transactions of the Royal Society B has shed new light on the popular saying “Birds of a feather flock together.” It has been observed that flocks of birds typically consist of a single species, with individuals that are virtually identical to one another, as the proverb suggests. However, a peculiar phenomenon has been observed in flocks of multiple species in Southeast Asia. Despite being distantly related, these species appear to adopt a similar physical appearance, as if attempting to blend in with one another.

As per a study co-authored by Scott Robinson, an Ordway eminent scholar at the Florida Museum of Natural History, the birds in Southeast Asia’s flocks share random features such as crests or yellow bellies that make them almost indistinguishable from one another. This likeness is probably a type of mimicry, which is not uncommon among birds. In contrast, the resemblance among multispecies flocks is different, according to lead author Rebecca Kimball, a biology professor at the University of Florida. This collective obscurity is suggested to offer unrelated birds a safe haven from predators who might otherwise isolate individual targets based on distinct color patterns. This theory, which was first proposed in the 1960s for flocks along the Andes Mountains, was largely abandoned after follow-up studies failed to provide conclusive evidence of mimicry in Andean multispecies flocks. Robinson and his colleagues observed this phenomenon in China’s multispecies flocks in 2010 and spent several years documenting similarities between species. While some similarities are subtle, the authors highlighted several visually conspicuous examples.

The Himalayan cutias in western Asia exhibit a striking and unique appearance with their mismatched layers of black feathers, chestnut wings, and zebra-striped white chests. However, the rufous-backed sibias that flock with them are able to imitate their markings remarkably well, despite lacking the distinctive stripes. Both species also exhibit similar behaviors and foraging patterns.

Interestingly, some birds are capable of mimicking multiple species as they mature. For example, juvenile white-hooded babblers resemble parrotbills in their rusty head feathers and brown wings, but as adults, they resemble white-crested laughingthrushes. This mimicry contributes to the diversity within multispecies flocks, and if it persists over time, it may even lead to the emergence of new species.

This phenomenon appears to be particularly prominent in China, where birds with similar traits tend to flock together and imitate each other’s markings. This suggests that two key factors may be necessary for this type of mimicry to occur: flocking behavior and physical traits that are distinct enough to be recognizable and imitated.

Overall, the role of mimicry in speciation is a fascinating area of study, particularly given the potential for these behaviors to contribute to the creation of new species over time.

According to Robinson, there are two key factors that contribute to the emergence of mimicry in flocks. Firstly, a flock must consist of a few dominant species, with some more common than others. This provides a model worth imitating for other birds, as they benefit from the same protection, resources, and compatible social group. However, in other parts of the world, flocks tend to have a more open-door policy, which weakens the selective forces that contribute to mimicry.

The second important factor is predation, particularly from raptors, which is a significant threat for small to medium-sized flocking birds. Southeast Asia is home to almost 30% of all raptor species, which puts enormous pressure on flocks and may promote mimicry. To confirm whether similarity among flocking species is a result of mimicry, extensive genetic analyses are required to rule out other potential causes.

Robinson also notes that the widespread nature of mimicry in birds has only been recently appreciated. The assumption that birds are closely related if they look similar, which forms the basis of taxonomy work, is now being challenged by genetic studies that reveal the role of social groupings and shared environments in shaping physical traits.

Source: Florida Museum of Natural History

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