SOCKMAN, K.W.*; HAHN, T.P.; WILLIAMS, T.D.; BALL, G.F.; Johns Hopkins Univ., Baltimore; Univ. of California, Davis; Simon Fraser Univ., Burnaby; Johns Hopkins Univ., Baltimore: Prior Experience with Photostimulation Accelerates Photo-induced Reproductive Development in Female European Starlings

Individuals reproducing early in the breeding season usually enjoy greater reproductive success than late breeders. For first-year female birds, breeding is typically delayed and reproductive success reduced compared to older, more experienced females. The mechanisms underlying advanced onset of breeding in older female birds are largely unknown. In photoperiodic species, experience with photostimulation in the first year of breeding may prime the reproductive axis to respond more rapidly to photic or other cues in subsequent years. To test this idea, we captured 32 juvenile (hence na�ve to photostimulation) female European starlings (Sturnus vulgaris) and held half of them on a photoperiod of 8-hours-light 16-hours-dark (8L 16D) for 20 weeks (photo-na�ve group). We held the other half on 16L 8D for 12 weeks and then 8L 16D for 8 weeks (photo-experienced group). When we subsequently transferred all birds to 16L 8D, photo-experienced birds had more rapid weight gain, which may be necessary for egg production in the wild. After 4 weeks of this photostimulation, oviduct mass, which is an indicator of circulating estradiol levels, and diameter of the largest ovarian follicle were greater in photo-experienced than in photo-na�ve females, even when we controlled for differences in body mass. Thus, experience with photostimulation accelerates reproductive development during subsequent photostimulation and may explain, in part, why older females breed earlier and have greater reproductive success than first-year females experiencing photostimulation for the first time. Experience with other factors, such as ecological and social cues, may also advance onset of breeding in older birds.