The post-ovulatory follicles of blackbirds (Agelaius)

Post-ovulatory follicles of tricolored blackbirds (Agelaius tricolor) and redwinged blackbirds (A. phoeniceus) regress from 6.0 to 3.0 mm in length by two days after ovulation and remain less than 3.0 mm during incubation. The follicles of females feeding young average less than 1.0 mm. Serial sections of ovaries of birds in all stages of the nesting cycle show distinct post-ovulatory follicles up to 25 days after ovulation. Lymphocytes, granular polymorphonuclear leucocytes, macrophages, and fibroblasts invade the sloughed granulosa and the hemorrhaged theca interna after ovulation. Granulosa cells, epithelioid cells in the theca interna, and connective tissue cells in the theca externa are lipoidal and cholesterol-positive for at least ten days after ovulation. The rapid regression and histological evidence of degenerating tissue and the invasion of cell types characteristic of the inflammatory response suggest that the ovulated follicles are degenerating rather than secretory organs.