Photoperiod Conditions Influence Fecal Estradiol Levels in Females of Migratory Reed Bunting Emberiza schoeniclus and Non-migratory Meadow Bunting Emberiza cioides.

Fecal estradiol levels in females of the migratory Reed Bunting Emberiza schoeniclus and non-migratory Meadow Bunting Emberiza cioides were measured by radioimmunoassay after extraction with ether. When the photoperiod conditions were changed stepwise from 10hr light/14hr darkness (LD 10:14) to LD 15:9, the fecal estradiol levels in the migratory Reed Bunting increased significantly at LD 12:12 and subsequently decreased at LD 14:10. A similar pattern of change was observed in the non-migratory Meadow Bunting. Fecal estradiol levels appear to reflect the levels circulating in plasma, indicating that estradiol levels circulating in plasma increase at LD 12:12 and subsequently decrease at LD 14:10 not only in the migratory Reed Bunting but also in the non-migratory Meadow Bunting.