Bird anatomy (The Angry Birds Movie)

"Oh. Easy, guys. Hollow bones. I've got hollow bones."

- Red, The Angry Birds Movie 2 In The Angry Birds Movie and its sequel, the characters of the Angry Birds franchise are depicted with actual limbs for the first time (not considering Angry Birds Transformers, Super Angry Birds and some other appearances of limbs). This article explains the variety of limbs that exist in the film and how these new aesthetics affect the original appearances of the birds.

Overview
The birds are depicted as winged creatures with legs that end in talons arranged in the anisodactyl form (three toes forward and one back). Despite such shape of their feet, Birds can wear human footwear without issue. As hatchlings, birds are born with small wings and legs, and a fat, round body. However, as they grow, birds can develop unique body shapes, wings, and legs. Birds, like Pigs, also do not have necks.

Wingspan
In the Angry Birds films, the birds have wings, which function exactly like human arms, instead of actual bird wings, as they contain dedicated hand-like skeletal structures. Most birds have a moderate wingspan, although there are some Birds who have short and small wings, such as Hal, and a few others with long ones, such as Stella and Gale. However, the colossal Mighty Eagle has proper wings which help him fly. A statue depicts this, carrying hundreds of eggs while several birds look up in awe (and Red strangely crying) at his heroism.

The bones of the Birds' wings, like their real-life counterparts, are hollowed out and somewhat fragile, even though they are not designed for flight.

Leg length
Birds typically stand on legs that are not too long, although some variations of the length exist, as with wingspan. Stella and Gale have longer legs to appear tall, exhibiting a sense of athleticism.

Leg type
Birds are covered in feathers, which may also cover their legs as well, down to the talons. However, there are also birds who do not have fully feathered legs. In such cases, the unfeathered portion of the legs is covered with scales, like the talons. The color of the scales and talons usually match the color of the beak, although there are exceptions, such as Bubbles. Birds can have half-feathered legs, such as Chuck, or they may have fully, scaly legs that are thin and twig-like, comprising nothing more of scales, bone and a thin layer of muscles, like that of Stella.

Eye size
Hatchlings have abnormally huge eyes, which cover the middle-top of their faces, but these progress into smaller eyes during adolescence or the eyes stay normal while their bodies grow bigger. An example is clearly detailed by looking at the hatchling Petunia, who clearly see has large eyes. However, examining adolescent birds such as Chuck and Bomb shows their eyes being smaller than their bodies.

Silver is a notable exception; her green eyes remain fairly large even while grown.

Different from other appearances, the birds' eyes are separated, instead of being together.

Trivia

 * The birds seem to use their talons as hands when they can't use their wings.