eBird

eBird is the most successful citizen science biodiversity project in the United States and it have been expending around the globe.

Go to http://ebird.org/content/ebird/ to learn about the project and register if you want to make and share your bird observations

There are free eBird apps for the iPhone and Android phones.

The site has many good features to keep track of your observations and to find out what other people are finding around the globe.