Physical Characteristics:
* Feathers vs. Fur: Birds have feathers, while mammals have fur or hair. This is the most obvious distinction.
* Wings vs. Limbs: Birds have wings, which are modified forelimbs used for flight. Mammals typically have four limbs, though some have adapted for specialized movement (e.g., flippers, hooves).
* Beaks vs. Mouths: Birds have beaks, which are hardened structures used for feeding. Mammals have mouths with teeth.
* Eggs vs. Live Birth: Birds lay eggs, while mammals give birth to live young.
* Warm-blooded vs. Warm-blooded: Both birds and mammals are warm-blooded, meaning they can regulate their own body temperature.
Other Differences:
* Respiration: Birds have a unique respiratory system that allows them to breathe efficiently during flight.
* Skeleton: Birds have a lightweight skeleton with hollow bones to aid in flight.
* Communication: Birds communicate using a variety of sounds, including songs and calls.
* Social Behavior: Birds can be highly social animals, often living in flocks or colonies.
Exceptions:
* Flightless Birds: Some birds, like ostriches and penguins, cannot fly.
* Mammals that Lay Eggs: Monotremes, like platypuses and echidnas, lay eggs, but they are still considered mammals due to other mammalian characteristics.
In summary:
While there are exceptions, feathers, wings, beaks, and egg-laying are the most reliable characteristics to differentiate birds from mammals.