People.com Celebrity Parents Rooney Mara Opens Up About 'Special' First Mother's Day as a New Mom: 'I Feel So Fortunate' In a heartfelt letter for Farm Sanctuary's Mother's Day campaign, Rooney Mara says raising son River has "opened my heart to a whole new life filled with hope" By Benjamin VanHoose Benjamin VanHoose Twitter Benjamin VanHoose is an Associate Editor on the Movies team at PEOPLE. He's worked at PEOPLE for over three years as a writer and reporter across our Entertainment, Lifestyle and News teams, covering everything from the Johnny Depp v. Amber Heard trial to the Oscars. He regularly covers red carpet events and has interviewed stars like Drew Barrymore, Ryan Reynolds and Kirsten Dunst. He previously worked as a copy editor at Topix Media Lab. People Editorial Guidelines Published on May 5, 2021 01:25 PM Share Tweet Pin Email Rooney Mara is sharing how becoming a parent has "opened her heart." The Carol actress, 36, and her fiancé Joaquin Phoenix welcomed their first baby last year, a son named River after Phoenix's late brother who died in 1993. In a new open letter as part of Farm Sanctuary's Mother's Day campaign, shared with PEOPLE, Mara opens up about life as a new mom while shedding light on mothers in the animal kingdom. "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," writes Mara. "I feel so fortunate to be able to nurture my son in all of the ways that nature intended," she continues, "and I wish all mothers in the animal kingdom could experience that sacred maternal bond with their young, devoid of exploitation by humans." Want to get the biggest stories from PEOPLE every weekday? Subscribe to our new podcast, PEOPLE Every Day, to get the essential celebrity, entertainment and human interest news stories Monday through Friday. Jon Kopaloff/Getty Images Joaquin Phoenix and Fiancée Rooney Mara Welcome First Child River, Honoring Actor's Late Brother Mara then highlights three "extraordinary" animals who "survived dire circumstances, healed from their traumas, and graciously share their affection with others" against all odds. Those include Henrietta turkey, Jackie cow and Cynthia goat. "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," adds Mara. "As I celebrate my first Mother's Day, I hope you will join me in honoring all of the inspiring moms and maternal figures who've made a difference in your life. With love, Rooney Mara." Mara and Phoenix, 46, first opened up about their lives as parents in an exclusive op-ed for PEOPLE in November, addressing the migrant children crisis at the U.S.-Mexico border.