Is it true that a bird always has nest?

The statement "a bird always has nest" is not entirely true. While many bird species construct nests as a place to lay and incubate their eggs and raise their young, there are some exceptions to this rule. Here are a few examples of birds that do not necessarily always have nests:

Emperor penguins: Emperor penguins (Aptenodytes forsteri) are remarkable for their unique breeding behavior. Instead of building nests, male emperor penguins hold the eggs on their feet, covered by a brood pouch, during the entire incubation period of about 64 days. The females leave the colony after laying the eggs and travel to the ocean to feed, while the males huddle together in large groups to protect the eggs from the harsh Antarctic winter conditions.

Common guillemot: Common guillemots (Uria aalge) are seabirds that often lay their eggs on bare cliffs or rocky ledges without constructing elaborate nests. These birds rely on their cryptic coloration and the inaccessibility of their nesting sites to protect their eggs and chicks from predators.

Pigeons and doves: Some species of pigeons and doves, such as the common wood pigeon (Columba palumbus), build flimsy platform nests made of twigs and branches. However, certain other species, like rock doves (Columba livia) and mourning doves (Zenaida macroura), may simply lay their eggs in a scrape on the ground, with minimal or no nest construction.

Great crested grebe: Great crested grebes (Podiceps cristatus) construct intricate floating nests made of aquatic plants on the surface of water. However, not all grebe species follow this pattern. For instance, little grebes (Tachybaptus ruficollis) build their nests close to the water's edge or among reeds.

Tinamous: Tinamous are a group of ground-dwelling birds found in Central and South America. They typically lay their eggs directly on the ground or in a simple depression without building a conventional nest.

Therefore, while many bird species do build nests, there are several exceptions to this rule, and not all birds always have nests.