An American biologist and author, he is known for his research on desert animals. He most famously published a scientific journal called The Condor, in which he detailed the life cycle of the Common Poorwill bird and other creatures.
From the beginning of his career, he took regular weekend excursions to the desert to study wildlife; the trips became known as Jaeger's palavaers and continued long after his retirement.
While teaching in Palm Springs, California, he formed a creative partnership with several noted wildlife artists and authors.
He was born in Loup City, Nebraska. He died at the age of ninety-six in Riverside, California.
Like television nature show producer Martin Kratt, Jaeger helped raise public awareness of nature and wildlife.