Investigation of reproductive fitness in living male European brown bares from different habitats

The reproductive fitness of 138 live male brown hares was assessed in the a nesthesized state. The used methods included the non-surgical evaluation of endocrinological, ultrasonographic and spermatological parameters in wild hares from 15 different areas in North Rhine-Westphalia. The study period w as the main breeding season (April 1998 and 1999) and the period of beginni ng testis involution (July 1999). The results showed a significant seasonal influence on testis volume and sperm production, but there are no indicati ons of any pathological changes of gonads and the reproductive tract. The h igh percentages of motile and intact spermatozoa demonstrate an unimpaired reproductive fitness. In some males with low ejaculate and/or sperm quantit y the analysis of testicular tissue (fine needle biopsy) did not show distu rbance of spermatogenesis. The variability of reproductive parameters betwe en the individuals did not show any relationship to the habitats with high or low hare population density. This relationship should be verified in fur ther studies including more animals. In conclusion, the results suggest tha t the decline in the European brown hare population is caused by an increas ed mortality rate rather than by a disturbed fertility.