Unlike mammals, birds lay eggs and initial stages of development occur outside the mother’s body. Reproductive system of birds The gonads develop from two sources during embryonic development. When ...

"I would say that any modern biologist would, or should, say that birds are reptiles," Martin Stervander, an evolutionary ...

Photograph by TUI DE ROY, MINDEN PICTURES During a courtship display, each male seeks to outdo the others with one body part ... of Nature ranks the bird “least concern,” but invasive species ...