All birds were separated and returned to isolation cages after having completed their assigned portion of the
cycle. Neither courtship experienced nor nestbuilding experienced females laid eggs during their 8 days in the
breeding cage or during their 5 weeks in isolation cages before testing. Beginning 4 weeks after they had been
returned to isolation cages, each bird received seven daily injections of 100 of progesterone in 0.1 ml of
sesame oil, injected into the right and left pectoral muscles on alternate days. The birds were tested in blocks
that included animals from each group in a block. The birds in group I received their injections at an age
comparable in time to those in group VI