How a small bird learns to imitate a snake
Evolution often surprises us with the strategies life uses to survive. It isn’t just about camouflage or color; sound can become a powerful tool for defense too. In Spain, a common songbird family member provides a striking example. Scientists documented that certain birds imitate the hiss of snakes when nests come under threat. 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 display a curious defense: they produce hissing noises that resemble the snoring of snakes, a tactic used to guard nests and deter intruders.
A study published in Current Zoology suggests that this defensive method may have evolved 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 tilts the balance in favor of the nest occupants.
A notable finding is that this acoustic mimicry seems rare and unusual, with researchers observing it occurring more often 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, heads held forward, and wings fluttering. The display gives the impression of a dangerous, coiled threat, and the bird makes a quick, sharp move that mirrors a serpent’s strike. The result is a dramatic, momentary defense that can stop an intruder in its tracks.
The researchers, led by Diego Gil from the MNCN, explored 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, especially for sounds made inside the nest. Other alarm calls did not show the same correspondence, highlighting a targeted mimicry rather than a general alarm signal.
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 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 spread prominently, enhancing the illusion of a dangerous snake and prompting the intruder to retreat.
A working system
In the study’s second phase, scientists asked whether the sound actually helps birds survive a intrusion or if the display is merely an instinctive bluff. A curious test subject was introduced to observe reactions. Swinhoe’s squirrel, also called the striped or Swinhoe’s tree squirrel, often feeds on eggs and young birds and can be trained to respond to alarm sounds.
When the team replayed the nest alarms to these squirrels, the animals avoided approaching the food source. The outcome supported the idea that nest hissing is real acoustic mimicry with a functional value, contributing to nest defense rather than a harmless ritual.
Across the study, researchers emphasize that the hoarse, snake-like hiss in nest defense is not a universal trait among all Paridae populations. Some individuals in the same habitats imitate snakes, while others do not. This variation points to evolutionary divergence and suggests mimicry can emerge in response to local predator pressures.
In summary, the 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 success of this tactic highlights a fascinating example of evolutionary convergence, where different lineages arrive at similar defensive solutions through behavioral changes 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 sounds.
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.