Research also revealed that even though young bucks do some of the breeding, mature bucks do most of it in populations with good age structure. Their research showed bucks 3½ years of age and older sired 70 and 85 percent of fawns, respectively, in populations with reasonable age structure and sex ratios. Thus, all yearlings and 2½-year-olds collectively only sired 15 to 30 percent of the fawns. This is much better than when yearlings and 2½-year-olds comprise 80 to 90 percent of the buck population, such as under many traditional deer management programs, and would thus sire nearly all fawns. The physical and nutritional stress of actively participating in the rut no doubt has an impact on the health and future development of these immature bucks. Also, does appear to select mates based at least partially on age – older does tend to select older mates. If older bucks are not available, older does may spend more time unsuccessfully wandering and searching for them. They will breed with younger bucks but it is typically later in the fall.