Walking a fine line between superb adaptability and severe procrastination, 50 female singers from southern Maine woke up last Saturday, the day of their concert, without ever having attended a practice session.

This was all by design, said Christine Ferguson, 59, of Poland.

Ferguson is the director of “Runnin’ Wild and Feelin’ Groovy,” an all-female a cappella recital put on by Yarmouth’s Royal River Chorus on the evening of Oct. 28 at the Windham High School.

The Royal River Chorus is a chapter of Sweet Adelines International, a music education association for women singers. The musical style the group employs, which utilizes four-part harmonies and no instruments, falls under the banner of “barbershop.”

“Runnin’ Wild” began with an hour of songs that Ferguson said reflected the busy lives women lead today. The Royal River Chorus members were all dressed in identical black outfits for the opening hour of the concert.

After the intermission the women received a flower-child makeover and sported bright headbands and bell-bottoms. The songs sang after this point were hippie-throwbacks like Age of Aquarius, by the 5th Dimension.

While the majority of the concert consisted of carefully choreographed and rehearsed songs by the Royal River Chorus, the last three songs featured a rush of young women aged 25 and under who stormed the stage with cartwheels and bright outfits.

Ferguson said the girls were recruited to take part in the Young Women in Harmony workshop of Sweet Adelines. The young women were all given three songs to learn, such as Dancing in the Streets, and told to arrive at the Windham High School at 8:30 a.m. the day of the show.

The girls spent the rest of the day rehearsing for the performance at 7 p.m. that night. They had not met as a group before that point.

“People who have seen our shows before said (the Windham show) was one of the best,” Ferguson said.