A new study released on Monday blames the extinction of an estimated 1,300 bird species native to the Pacific Islands on the arrival of humans to the area nearly 4,000 years ago.

The study, conducted by the Zoological Society of London (ZSL), examined fossils from 41 islands and used a new technique to gauge how many animals they do not have fossils for in order to come up with the number 1,300, according to Tim Blackburn, professor and director of the ZSL's Institute of Zoology.

In all, researchers identifiied 160 species of non-passerine land birds (non-perching birds with feet designed for specific functions such as webbed feet for swimming) that went extinct after humans first arrived in the Pacific Islands. From there, Blackburn believes the total can then be estimated for other types of birds.

"If we take into account all the other islands in the tropical Pacific, as well as seabirds and songbirds, the total extinction toll is likely to have been around 1,300 bird species," he said.

Among those lost include several species of the large, flightless bird from Hawaii known as the moa-nalos, as well as the New Caledonia Sylviornis, a relative of the game birds that weighed an estimated 65 pounds - three times the weight of a swan.

Extinction is believed to have been a result of overhunting as well as deforestation and the general destruction of the birds' habitat. This was especially true for smaller, dryer islands where natural resources were reduced much faster and offered the birds' few hiding spaces from hunters, researchers said. What's more, flightless birds were more than 30 times more likely to become extinct than those that could fly.

Ultimately, the extinction of Pacific Island birds did not stop with the initial arrival of humans: an estimated 40 species went extinct once Europeans arrived and, as the press release states, many more species are still threatened today.

The Center for Biological Diversity is one non-profit working to reverse this trend. Over the years it has worked to gain Endangered Species Act protections for many different species residing in the region of the world, including birds. Since 2000, the group has secured listing and critical habitat designation for over 24 rare species from Guam, American Samoa and the Northern Mariana Islands.