Birds "blend in" to adapt to diverse environments

In a recent study published in the journal Philosophical Transactions of the Royal Society B, researchers are exploring the phenomenon of multispecies flocks of birds in Southeast Asia that seem to converge on a similar appearance, even when they are distantly related. 

Study co-author Scott Robinson of the Florida Museum of Natural History commented on this curious observation: “They all share haphazard traits, like crests or yellow bellies, which makes them almost identical. You can’t really tell them apart without looking at their markings.”

This similarity in plumage is thought to be a type of mimicry, which is not uncommon in birds. Alfred Russel Wallace, the co-discoverer of natural selection, was the first to suggest that some bird species engage in mimicry when noting the similarities between orioles and friarbirds in Australia. Birds can mimic one another to reduce aggression from a dominant species, to resemble a more formidable adversary to predators, and in at least one case, to make themselves appear toxic.

However, study lead author Professor Rebecca Kimball from the University of Florida believes that the resemblance in multispecies flocks is a different form of mimicry. 

“In mimicry, you often want to look like something because there’s an advantage to being that other thing. You want species to think you’re toxic or low-profitable prey,” said Professor Kimball. “In flocking birds, one idea is that this has more to do with a predator’s ability to isolate a target. When there are a bunch of birds moving around, it may be easier for predators to identify an individual that has a distinct color pattern.”

This idea of unrelated birds finding safety in collective obscurity was first proposed in the 1960s for flocks along the Andes Mountains, but follow-up studies failed to show conclusive evidence of mimicry in Andean multispecies flocks, and the theory was largely abandoned. However, Robinson began observing a similar phenomenon in 2010 while working with a Chinese colleague in Yunnan province. Over the next several years, he and his colleagues documented similarities in China’s multispecies flocks, uncovering the same pattern repeatedly.

What the researchers discovered

Robinson and his team found examples of birds that mimic more than one species as they mature, as well as birds whose appearances vary across their range. Somewhat counterintuitively, this conformity within multispecies flocks may be contributing to diversity in the region. If these differences persist long enough, Robinson said, it might ultimately result in one species becoming two.

The researchers believe there are two main ingredients required to create this type of mimicry in flocks, both of which might help explain why this pattern appears to be so prominent in China but absent elsewhere. First, a flock must be composed of just a few species, with some more common than others. Second, the flock must face significant predation pressure, which is the case in Southeast Asia, where the region harbors almost 30% of all raptor species.

The experts plan to conduct wide scale genetic analyses to determine whether similarity among flocking species is the result of mimicry or other potential causes. “Just how widespread mimicry is in birds is something that’s only been appreciated recently,” Robinson said. “Taxonomy work is based on appearance, with the assumption that birds are closely related if they look similar. Now that we can study DNA, we’re realizing they often look alike because they live together.”

More about bird mimicry

Bird mimicry is a fascinating natural phenomenon where one bird species imitates the appearance, sounds, or behaviors of another species to gain an advantage. There are several forms of bird mimicry, each serving a different purpose:

Batesian mimicry

In this form of mimicry, a harmless bird species imitates the appearance of a dangerous or unpalatable species to deter predators. By resembling a toxic or unprofitable prey, the mimicking bird reduces its risk of being attacked. For example, the Viceroy butterfly mimics the toxic Monarch butterfly, deterring predators that have learned to avoid the Monarch.

Müllerian mimicry

This occurs when two or more unpalatable or dangerous species resemble each other. Predators learn to avoid both species because of their shared appearance, providing a mutual benefit to both mimicking species. An example of this type of mimicry is found in some species of Heliconius butterflies, which share similar color patterns to warn predators of their unpalatability.

Aggressive mimicry

Here, a predatory bird species imitates the appearance, sounds, or behaviors of a harmless species to deceive its prey. By blending in with the harmless species, the predator can get closer to its prey without raising suspicion. For instance, the Zone-tailed Hawk resembles the Turkey Vulture in appearance and flight behavior, allowing it to approach prey unnoticed.

Vocal mimicry 

Some birds are capable of imitating the songs and calls of other bird species, as well as non-bird sounds. This type of mimicry serves various purposes, such as attracting mates, confusing rival birds, or avoiding predators. Notable vocal mimics include the Northern Mockingbird, which can imitate up to 200 different bird songs, and the Lyrebird, known for its remarkable ability to mimic various sounds, including chainsaws and camera shutters.

Bird mimicry is an adaptive strategy that has evolved in response to various ecological pressures, such as predation, competition, and reproduction. As a result, these remarkable adaptations showcase the complex relationships that exist within bird communities and ecosystems.

Other examples of remarkable bird adaptations

Birds have evolved numerous adaptations to help them survive and thrive in diverse environments. These adaptations are often related to their feeding habits, locomotion, reproduction, and other aspects of their biology. Here are some examples of bird adaptations:

Beak shape 

Birds have developed various beak shapes to suit their feeding habits. For example, hummingbirds have long, slender beaks for sipping nectar from flowers, while raptors have sharp, hooked beaks for tearing flesh from their prey. Finches, on the other hand, have strong, conical beaks for cracking seeds.

Feet and leg structure 

Different bird species have specialized feet and leg structures that enable them to exploit various habitats and food sources. Wading birds like herons have long legs and wide-spreading toes for walking in shallow water, while woodpeckers have zygodactyl feet (two toes facing forward and two backward) for clinging to tree trunks.

Wing shape

The shape and size of a bird’s wings can influence its flight capabilities. Albatrosses have long, slender wings for efficient gliding over vast ocean expanses, while birds of prey have broad wings with slotted tips for soaring and maneuvering during hunting. Swifts and swallows have short, tapered wings for rapid, agile flight.

Camouflage

Many bird species have evolved coloration and patterns that help them blend into their environment, making them less visible to predators or prey. For example, ground-nesting birds like the Common Pauraque have cryptic plumage that closely resembles leaf litter, while Arctic birds like the Snowy Owl have white feathers that help them blend into snowy landscapes.

Migration

Some birds have adapted to migrate long distances to exploit seasonal resources or escape harsh weather conditions. For example, the Arctic Tern breeds in the Arctic during the summer and migrates to the Antarctic for the southern hemisphere’s summer, covering around 25,000 miles each year.

Nesting behavior

Birds have developed various nesting strategies to protect their eggs and young from predators and environmental factors. Some birds, like the Weaver, construct elaborate hanging nests from grasses and other materials, while cavity-nesting birds like the Eastern Bluebird use tree cavities or nest boxes for shelter.

Vocalizations

Birds have evolved complex vocalizations to communicate with one another. These vocalizations serve various purposes, such as attracting mates, defending territories, or warning of predators. The intricate songs of the Song Sparrow and the mimicry abilities of the Northern Mockingbird are examples of this adaptation.

These are just a few examples of the countless adaptations that have allowed bird species to survive and flourish in a wide range of environments and ecological niches.

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By Chrissy Sexton, Earth.com Editor

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