Gonadal status upon spring arrival in long-distance and short-distancemigrating stonechats ( Saxicola torquata)

Long-distance migration is often associated with relatively short breeding seasons and a start of reproductive activities shortly after arrival. The full activation of the reproductive system from the regressed state takes, however, several weeks and must, therefore, be initiated in the winter quarters or during spring migration. Hence, long-distance migrants face a potential con.ict between the energetic and temporal requirements of migration and the preparation for reproduction. We studied long-distance migratory Siberian stonechats in northern Kazakhstan and shortdistance migratory European stonechats in Slovakia. We hypothesized that migratory distance and gonadal status at the time of arrival are related. We found that males of both populations arrived with gonads that were not fully developed. However, the populations neither di.ered in gonadal state at the time of arrival, nor in the rate of testicular development to the fully active state at the time of egg laying.

Michael Raess, Eberhard Gwinner, J Ornithol (2005) 146: 325-331