Local Variations in the Time of Breeding of Female Blue Grouse

Abstract

Timing of breeding of female blue grouse [Dendragapus obscurus] was studied in 2 populations living about 2-3 km apart. Timing of breeding varied among years, between populations, and between adults and yearlings. Variations in time of breeding among years showed some correlation with annual differences in April weather. Breeding was about 1 wk later on the area that was higher in elevation, cooler, wetter, had more snowpack and held its snowpack longer in spring. Most yearling females copulated only after most adult females were beginning to nest. The period of copulation was up to 10 wk long in adult females but only up to 7 wk long in yearlings. Most females were on breeding range only about 2-3 wk prior to copulation. While there was a 3-4 wk difference in timing of loss of snow between areas, there was only a 1 wk difference in timing of breeding. Differences in timing of breeding between age classes may relate to differences in physiological maturity, amount of time on the breeding range prior to copulation, harassment of yearlings by adults or interactions among new recruits (yearlings) themselves. Proximate control of the reproductive cycle of females appears most subject to local ecological conditions. The breeding period of males has likely been selected to cover the entire receptive period of females, including annual, goegraphical and age-class variations.