The penduline tit is a genius when it comes to architecture: its nest has a hidden entrance, while the visible opening leads to an empty pocket to trick predators.

The penduline tit (Remiz pendulinus) belongs to the bird family Remizidae. Its name, penduline, refers to the hanging bag nests that the bird builds for its eggs. While the shape and form of the nest are quite impressive just by themselves, it also has a very unique and important defense mechanism: a hidden entrance.

They pay a great attention to detail when it comes to building a nest. It even has a fake entrance. Image credit: Daniele Colombo

These birds can be found in Eurasia, Africa and North America. They range from 3 to 4,3 inches (7.5 to 11 centimeters) in length, and sport a brown back, gray head and a distinctive black mask. The markings of some subspecies could also include other colors as well. For example, the European penduline tit has black and chestnut markings.

These skillful architects build pear-shaped nests on the branches of willow or birch trees. First, the male begins the construction of the nest by attaching plant fibers and fluffy seeds to the twigs and branches. Then, with the help of the female, they vow the other parts of the pouch-like nest with spiderweb, wool, animal hair, and other soft plant material. The result is a very elaborate nest that is suspended from the tree.

In order to protect themselves and their eggs, the penduline tit has developed a very clever design. Their nests incorporate a fake entrance right above the real opening. This false entrance leads to an empty chamber. The birds can enter the real nesting chamber by opening a hidden door. Since this flap is partly composed of sticky spider webs, they can easily close it from the inside after they enter, or when they are leaving the nest.

So when a predator – a snake, for example, tries to enter the nest of the penduline tit in the hopes of an easy meal, it’s gonna find itself in an empty pouch of the nest. This will make the disappointed predator leave, thinking that no one is there, while the birds and the eggs are safely hidden in the other part of the nest that is not accessible through the fake entrance.

The survival strategy of this small bird is truly amazing and unique. Image credit: António Pena

Although it’s not exactly known how this survival strategy was developed in these birds, by creating these fake entrances, penduline tits likely follow an instinctive pattern. This means that over the course of millions of years, the birds who were following these behaviors probably had a little more chance of surviving, and they passed their genes on to the next generations.