A Four-Year Study on Reproductive Status and Life History of Wild European Brown Hares (Lepus europaeus)
Since 1991 the European brown hare (EBH) (Lepus europaeus) has been classified as a CITES species in Germany within six states, at last listed as a vulnerable species in Nordrhein-Westfalen in May of 2000. Based on the critical situation of a nation-wide population decline, a basic research study on reproductive biology in free-ranging EBH was initiated in 1998. In general, population dynamics are mainly influenced in terms of successful pregnancies, birth rate, and postpartum survival rates. This joint project included the non-surgical evaluation of health status, reproductive fitness, and monitoring of life history of new-born. A total number of 302 EBH (142 females, 160 males) from 16 different areas were assessed by using endocrinology, ultrasonographic, and spermatologic parameters. Different ultrasound techniques (B-mode, color flow Doppler, and 3-D ultrasonography) were applied in both sexes to image the entire urogenital tract, including blood flow inside reproductive organs, heart activity of individual concepti, and to the precise pregnancy stage and integrity. Semen collections were performed with specially designed electroejaculation equipment adapted to the male hare anatomy. Additionally, blood samples were examined to detect several important viral and bacterial pathogens using different diagnostic methods (an ELISA to detect the agent of European brown hare syndrome, serology screening for Brucella sp., Yersinia sp., tularemia, and Toxoplasma sp., and immunohistology to detect Toxoplasma sp.).
Of animals tested, 68.08% of the females were pregnant, 19.86% lactating, and in average 2.12 implantation sites per pregnancy were counted. Only 12.06% of females were non-pregnant and non-lactating, however, these individuals also showed ovarian activity. Mean serum concentrations of blood-plasma-progesterone were 97.9 ng in pregnant and 14.5 ng in non-pregnant females. Electroejaculation was practiced successfully in 134 cases. Each semen sample was assessed concerning volume, sperm concentration, motility, and morphology. In 13.75% of the males oligozoospermia was supposed, however, flow-cytometric-analysis did not show disturbance of spermatogenesis in this group. In addition, thermography technique (emerge vision, TM) was used to detect neonates in the natural environment. These new-born hares were monitored at night until they left the birth place naturally wise or they were hunted by foxes and birds of prey. These results did not indicate any kind of depression in reproduction or general health status monitoring of new born and juveniles results in a low abundance. Population development seems to be mainly determined by a high postnatal mortality and reduced survival rates.