Donato and Birk are both originally from the Houston area. Donato attended Cypress Woods High School before going on to West Virginia, while Birk went to Seven Lakes High School before attending Texas A&M.
The Astros have now signed 19 of their 40 selections, including eight of their top 10 picks.
Meanwhile, Astros general manager Jeff Luhnow said he still expects first-round pick Forrest Whitley (No. 17 overall), a right-handed pitcher from Alamo Heights High School in San Antonio, to sign before the July 15 deadline. Luhnow said there have been preliminary talks, but there's no rush to get him signed at this point.
"We're excited about the selection and we're optimistic about getting it done," he said. "We want to get it done as soon as possible. We don't want to go up against the deadline. There's no reason to, anyway. We know what we can offer him. We're going to make him an offer. I hope he likes what he hears from the Astros.
"He's got a nice option to go to Fresno State and pitch in Division I baseball for three years, but also three years from now he could be in the big leagues. That's what we're trying to convince him."
Jordan Ray is a reporter for MLB.com based in Houston.