He remained in Berlin until 1977 when the Cosmos of the North American Soccer League purchased his contract.

[2] Birkenmeier was the Cosmos' starting goalie for three consecutive Soccer Bowls ('80, '81 & '82), and did not concede a goal in any of them.

The Express folded two-thirds of the way through the season and on 6 March 1987, the Los Angeles Lazers signed him to a ten-day contract.

[5] In 1988, he played for the New York Pancyprian-Freedoms of the Cosmopolitan Soccer League as it went to the semifinals of the National Challenge Cup.

[11] On a visit back to his hometown of Hartheim in 2009 to celebrate his 60th Birthday, he described initially having mixed feelings about leaving Germany to play in the United States.

In the same interview, he stated that he goes back home to Hartheim every year to visit his brother and sister and stays abreast of hometown news via the internet.