Effects of prolactin on the gonad and body weight of the male pied flycatcher during the breeding period.

In the studies concerning the regulation of testicular regression in the pied flycatcher, the antigonadal effect of ovine prolactin has been examined. The species is a migratory, hole-nesting bird. Males were given daily injections of 200 microgram prolactin for 14 days. No antigonadal effects were observed. The body weight of the prolactin treated males was significantly higher than that of the control group.