An expedition to study frog habitats in Northern California’s Shasta-Trinity National Forest was cut short last week, with a father-son duo accused of taking two federal biologists hostage. The pair, identified as Joseph Charles Henrichsen and his adult son Phoenix Henrichsen, have been charged with kidnapping two US forest service researchers at gunpoint, NBC reports. Using a semi-automatic rifle, the Henrichsens are alleged to have kidnapped t…