Migrating birds in great numbers had to fly farther and longer looking for other wetlands, as their food sources were no longer available to them for their long flights. In some areas, weather even changed. As the wetlands were converted for all the various reasons, natural wetland ecosystems drastically changed or disappeared entirely. Millions of acres in the United States have been converted for other uses, and those millions of acres of wetlands and their crucial functions have been lost. Most tropical countries have lost more than half of their mangrove forests to logging, urban development, or conversion to rice fields, cropland or fish-farming ponds.
Mangrove swamps are saltwater swamps which lie along tropical seacoasts.
Along with the destruction of wetlands, human beings added pesticides and pollution, so over the years wildlife and bird populations greatly declined. All over the world, the values of wetlands were not realized, and so they continued to be drained and were converted to other uses. Click on underlined text. Mouse over images - if you see a little hand, click on it. Add a Free Dictionary Button to your browser so you can highlight words you don't understand and have the definition pop up on your screen.