Q.Birds need to keep their body light to help in flying. Hence, they show presence of some organs only on one side. How their skeleton helps in reducing their weight?

Altricial young hatch helpless and dependent on parents; precocial young hatch already capable of independent movement and feeding.

Bird (and some other vertebrate) hatchlings are classified into two broad categories based on their state of development at hatching:

Altricial hatchlings

• Hatch in an immature, underdeveloped state.
• Typically blind (eyes closed), naked (no feathers/down) or very sparsely feathered, and largely immobile.
• Completely dependent on parents for warmth, protection and feeding for an extended period after hatching.
• Examples: pigeon, crow, sparrow, and most passerine (songbird) chicks.

Precocial hatchlings

• Hatch in a well-developed, mature state.
• Eyes open at hatching, body covered with down/feathers, and legs strong enough to stand and walk almost immediately.
• Able to leave the nest soon after hatching and can often feed themselves (or at least follow the parent to food) with much less parental dependence.
• Examples: domestic fowl (chicken) chicks, ducklings, and megapode chicks. …

Ducks (class Aves) show several peculiar adaptive characters suited to a semi-aquatic, swimming and filter-feeding life.

• Webbed feet: the toes are joined by skin webs, acting like paddles that make swimming efficient.
• Broad, flat bill: fitted with comb-like lamellae along the edges, used to filter small food particles (plants, small invertebrates) out of water and mud.
• Waterproof plumage: ducks have an oil (uropygial/preen) gland near the tail base; they spread this oily secretion over their feathers using their bill, which repels water and keeps the feathers from getting waterlogged, aiding buoyancy and insulation. …