There are many conservation organizations in North America, but here is a list of some of the most well-respected organizations. Birds are not the primary focus of many of them, but conservation efforts that protect habitat for other organisms end up protecting birds as well.
The Nature Conservancy is one of the premier conservation organizations, working across the globe to protect species and their habitats, and not just for birds. It was formed in 1954 in New York using the approach of purchasing lands, then setting them aside, as a means for conservation. Since then, they've expanded their reach to include education, providing expertise for politicians, and much more.
The National Audubon Society is the oldest nationwide bird conservation organization in existence. It was formed in 1896 as the Massachusetts Audubon Society, followed by state-wide groups across the country. By 1901, the state-level organizations joined to form a rather loose national coalition, and the National Audubon Society was officially created in 1905. Initially, the organization focused on the protection of waterbirds, such as herons, egrets, gulls, and terns, but broadened their scope to work for the conservation of all birds.
The Cornell Laboratory of Ornithology came into existence in 1915 when Arthur A. Allen became one of the first professors of ornithology in the country, and posted a sign on his office door declaring a "Laboratory of Ornithology." Since then, the Lab has grown into an internationally renowned organization promoting conservation of birds and nature through a focus on research. In recent decades, the Lab has incorporated citizen science as a way to gain a greater understanding of birds, but also to energize the public in support of conservation.
Ducks Unlimited was formed in 1937 in order to conserve habitat for waterfowl. Its initial emphasis was on conservation for hunting purposes, but its focus has broadened to an emphasis on conservation in general. Its primary purpose is still the conservation of wetlands and other habitats used by waterfowl, but not just for hunting purposes.
Quail Forever is an organization focused on the conservation of habitat for quail, pheasants, and grouse, as well as other species that occur in those habitats. When Quail Unlimited folded in 2013, Quail Forever, which was a separate organization, became the premier conservation organization for quail and related species. While focusing on conservation, they also have a strong emphasis on hunting these species.
The Sierra Club was formed initially for the conservation of the Sierra Nevada Mountains of California. Since its beginnings, it has grown into an organization working to promote environmental health, including clean air and clean water. It works with a variety of groups to advocate for policies and regulations conducive to a healthy environment, and also to educate citizens on environmental issues.
There are many other conservation and environmental organizations in North America, as well as around the globe, and these are too numerous to name here. Many are focused on local or regional issues, and deserve your support. We wish we could list all of them here, but that's not practical, so we decided to focus on several of the larger, more widely recognized organizations.