How a small bird learns to imitate a snake
The way evolution shapes how species respond to threats often surprises us. It isn’t only about camouflage or color; sound itself can become a powerful tool for defense. In Spain, a common songbird family member shows a striking example. A group of scientists documented that certain birds imitate the hissing sounds made by snakes when their nests come under danger. This behavior appears to help protect eggs and fledglings from predators.
The family Paridae is easy to spot in forests and many other habitats. In Spain, familiar species such as the great tit and the blue tit show a curious defense: they produce hissing noises that resemble the snoring of snakes, a strategy used to guard their nests and deter intruders.
A study published in Current Zoology suggests that this defensive method may have evolved because it helps to create a snake-like alarm that predators and rivals find threatening. Like many animals, these birds fear snakes and vipers, so mimicking a snake often shifts the balance in favor of the nest occupants.
A notable finding is that this acoustic mimicry seems rare and unusual, and researchers observed that it may occur more in female birds within some populations.
How does a small bird imitate a snake?
When a predator approaches nests of certain Paridae species, individuals respond with a loud hiss, their heads stretched forward, and wings fluttering. The behavior gives the impression of a dangerous, coiled predator, and the bird makes a quick, sharp move that mirrors a serpent’s strike. The effect is a dramatic display intended to discourage a would‑be attacker, a momentary yet often decisive defense.
The researchers, led by Diego Gil from the MNCN, examined the mechanism behind this imitation. They compared the acoustic profile of more than forty recordings from six Paridae species with the snoring sounds produced by fourteen snake species belonging to vipers and elapids. They found strong similarity, but mainly for sounds produced inside the nest. Other alarm calls did not show this correspondence, underscoring a targeted mimicry rather than a general alarm call.
The classic scene is described as the great tit defense. When a predator nears the nest, the female lifts her head, fluffs her crest, and blinks and flares, while wings sweep and tail feathers fan out. The unmistakable hiss is delivered in a rapid, explosive burst as the head snaps and the mouth opens, followed by a downward wing stroke that brushes the nest cavity. The tail feathers are displayed prominently, adding to the illusion of a dangerous snake and prompting the intruder to retreat.
A working system
In the second phase of the research, scientists asked whether this sound actually helps birds survive an intrusion or if the display is simply an instinctive or cosmetic bluff. They brought in a curious test subject to observe reactions. Swinhoe’s squirrel, also known as the striped or Swinhoe’s tree squirrel, often feeds on eggs and young birds in this system and can be trained to respond to alarm sounds.
When the team played back the nest alarms to these squirrels, the animals avoided approaching the food source. The result supported the idea that the nest hissing is a genuine acoustic mimicry with functional value, contributing to nest defense rather than being a harmless ritual.
Across the study, the same researchers emphasize that the hoarse, snake-like hiss in nest defense is not a universal trait among all populations of Paridae. Some individuals within identical habitats imitate snakes, while others do not. This variation points to evolutionary divergence and the possibility that mimicry can arise in response to local predator pressures.
In summary, this research supports the view that some birds evolved snake-like hisses as a specialized defense. Predators confronted with a convincing coiled illusion tend to retreat, improving the odds for the bird’s offspring. The apparent success of this tactic highlights a fascinating example of evolutionary convergence, where different lineages arrive at similar defensive solutions through changes in behavior over tens of thousands of years.
These findings align with broader ideas about how birds and snakes rarely share a direct ancestor yet can develop parallel strategies to reduce predation risk. The study suggests that natural selection favors acoustic mimicry when it reliably lowers the chance of nest predation. Not all individuals possess this trait, and there is notable variation within populations, indicating a dynamic balance between predators, prey, and the costs of producing such calls.
Reference work: a recent study in Current Zoology details these findings and provides the methodological groundwork for understanding how acoustic mimicry operates in birds. This work highlights the importance of context, nest location, and predator behavior in shaping whether mimicry evolves and persists in a population.
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