Over millions of years, birds developed as a species. this relates to

*Over million of years, birds developed as a species. This relates to evolution. 

As you say birds developed as a specie but over million of years, the gradual change or development is called evolution. Also we can understand the word is evolution because as we know, scientist believe birds evolved from dinosaurs; meaning dinosaurs had to gradually change to fit as what we know today as birds.

Wetlands form where water and land meet. a lake with a wetland fringe can fill in with decayed plant and animal material to become a wet meadow. a pond can fill in to become a bog or fen. sediment can fill in a river marsh to become a swamp.flooding of coastal lowlands from rising sea levels has created broad coastal marshes that are protected from wave action by barrier islands or reefs. coastal wetlands also form when rivers deposit sediment as they reach the ocean. plants then take root and hold the soil firm against the forces of tides and waves.