eBird
eBird is a free online database that invites recreational and professional bird watchers to report bird observations, thereby allowing researchers to document and model bird distributions. eBird is provided by the Cornell Lab of Ornithology and National Audubon Society.
An observer can simply fill out information about the location, time, and other specifics related to a sighting, and automated filters review submissions before they are entered into the database.
Observations for each species are plotted over time, allowing researchers to determine migratory patterns, and interpret relationships to other environmental factors such as weather, landscape, and vegetation growth. Since data is not uniformly submitted across the world, complex models are created to predict species distributions.