Smithsonian Networks launched a standalone subscription-video streaming service, the latest TV programmer to branch into the over-the-top world as a hedge against a slowly shrinking pay-TV universe.

The ad-free Smithsonian Earth service, available for $3.99 per month initially on the web and Apple TV and Roku devices, promises “spectacular original nature and wildlife content.” Programming will be available in Ultra HD 4K format on compatible devices, including the Roku 4 player.

Content on Smithsonian Earth will be entirely separate from the programming that runs on Smithsonian Channel or the cabler’s apps and other digital outlets, according to a rep. Smithsonian Networks is a joint venture between Showtime Networks and the Smithsonian Institution.

The original shows in the OTT service, to be refreshed on a weekly basis, include a mix of documentaries and short series, covering such topics as the sea life of Socorro Island off the West Coast of Mexico to the creatures of Madagascar and active volcanoes in Ethiopia. The “Nature Scenes” series promises vistas of “the most breathtaking and wildest places on Earth.”

Additional series include “Great Blue Wild,” which takes viewers deep beneath the oceans, and “Nomads of the Serengeti,” about the annual migration of 2 million zebras and wildebeest from the Serengeti plains to the grassy highlands.

The company said 1% of subscription fees will be donated to Smithsonian Institution research and conservation initiatives. Smithsonian Earth, available only to customers in the U.S., is offering a free seven-day trial subscription to new customers.

Smithsonian Earth joins a growing list of Internet-delivered video services launched by TV networks, including HBO Now, Showtime, CBS All Access and NBCUniversal’s Seeso comedy channel. Also worth noting in the OTT field: CuriosityStream, an ad-free SVOD service with nature and science programming, which was launched earlier this year by John Hendricks, founder of Discovery Channel.