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The testicular cycle of blue grouse (Dendragapus obscurus fuliginosus) and its relation to age, breeding behavior and migration Simard, Benjamin Raymond-Marie


The testicular cycle of blue grouse (Dendragapus obscurus fuliginosus) has been studied from the testes of two hundred and twenty-four birds collected on their summer range on Vancouver Island over the years 1958 to 1964. For two age classes, adult and yearling, the characteristics of the following cycles were compared and correlated. The cycle of increase in size of the testes, the cycle of increase in diameter of the seminiferous tubules, the cycle of the development of the stages of spermatogenesis, the cycles of relative and absolute increase of the interstitium and the cycles of abundance of interstitial cells. Samples of sperm from these two age classes were compared. Furthermore, these cycles were compared with migration, with the period of egg laying in the female, with behaviour, with age of the bird over two years of age and with body weight. In all these tests, the yearlings had a shorter breeding cycle characterised by a slower recrudescence, a delayed and shorter breeding period, a faster and an earlier regression. Although the yearlings had smaller testes and a lesser amount of tubular tissue, they all seemed to develop all the stages of spermatogenesis and to produce fertile sperm. The smaller amount of intertubular tissue in yearlings was suspected to be correlated with their secretive behaviour and the smaller growth of the testes of the yearlings was attributed to an inherited character rather than to inhibition by the environments, No difference was found in the testicular cycle between hooting and silent males and between replacement or territorial yearlings and silent ones. It was concluded that all male birds present on the breeding range were apparently potential breeders. Smaller interstitium and delayed maturity seemed to be the main factors preventing the young birds from adding to the population of breeders.

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