Weather Factors and Spermatogenesis in Birds

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Abstract
Summary.: The testes and stomachs of four species of woodland passerine birds were examined on 13th to 15th March, after the exceptionally severe winter of 1946‐47. A similar examination was made at exactly the same time of year after the exceptionally mild winter of 1947‐48. The overall and tubular diameters of the 1947 testes were much smaller than those of 1948. In no instance in 1947 birds had spermatogenesis passed beyond the primary spermatocyte stage. All 1948 testes contained secondary spermatocytes, two species had undergone spermatogenesis and individuals of all species contained some fuchsinophil cells in the interstitium. Stomachs were almost devoid of animal food at time of collection after the “hard” winter, but contained appreciable quantities of normal food after the mild one. Despite the arrested development at the primary spermatocyte stage in mid‐March, 1947, at least three species bred at about the normal time following a sharp (higher than normal) rise in temperature and sunshine in April. Following the abnormally warm winter of 1947‐48 three (and probably four) species bred abnormally early. The results indicate that proximate factors other than the number of hours of daylight and resultant activity are significant in the timing of breeding seasons in birds. Temperature and sunshine may play an important rôle in some species.