Rooney Mara says motherhood has made her “more determined than ever” to help create a “kinder and more sustainable world”

And in an open letter written as part of Farm Sanctuary’s Mother’s Day campaign, Rooney has said she feels “fortunate” to be able to care for her son in “all of the ways that nature intended”, and said she wishes “all mothers in the animal kingdom” were as lucky.

In the letter, obtained by People magazine, she wrote: "As a new mom, Mother's Day has taken on a special meaning this year. Raising our baby, River, has opened my heart to a whole new life filled with hope and more determination than ever to create a kinder and more sustainable world.

“I feel so fortunate to be able to nurture my son in all of the ways that nature intended, and I wish all mothers in the animal kingdom could experience that sacred maternal bond with their young, devoid of exploitation by humans."

Rooney went on to highlight three "extraordinary" animals who "survived dire circumstances, healed from their traumas, and graciously share their affection with others" against all odds.

She concluded: "A Mother's Day adoption is a gift that keeps giving and supports the wellness of wonderful Sanctuary moms like Henrietta turkey, Jackie cow, and Cynthia goat.

“As I celebrate my first Mother's Day, I hope you will join me in honouring all of the inspiring moms and maternal figures who've made a difference in your life. With love, Rooney Mara."

The ‘Her’ actress and Joaquin, 46, welcomed their son in September, but waited until November to open up about their lives as parents when they addressed the migrant children crisis at the US-Mexico border.