Wincentz, T. 2009.
In recent decades the brown hare (Lepus europaeus) in <st1:place w:st="on"><st1:country-region w:st="on">Denmark</st1:country-region></st1:place> has undergone a substantial decline, but proximate causes are unknown, and little is known about actual densities. In this thesis, hare populations are investigated with respect to age composition and reproductive parameters in relation to habitat and phenotype, and point transect counts are evaluated in assessing hare densities. Data from culled individuals suggest that contemporary reproductive parameters and juvenile recruitment vary across <st1:place w:st="on"><st1:country-region w:st="on">Denmark</st1:country-region></st1:place> , while adult survival seems constant across populations. Juvenile recruitment (indexed as the proportion of hares culled in autumn comprised by individuals < 1 year) is lowest in areas with low densities, but unrelated to the reproductive output of females indexed as the mean number of placental scars, indicating high spatial variation in post-natal survival of offspring. Some variation in the demographic and phenotypic (size, weight) parameters is attributable to habitat composition. In a historical perspective, the proportions of juveniles in game bags dropped significantly between the 1950ies when hare populations where stable and the 1980ies and later, when hare populations according to bag size decreased with 5% annually. Simple matrix population models based on the estimated annual survival for adult females at present and the estimated fecundity for the 1950ies, 1980ies, 1990ies and since 2000, predicted the same population growth rates for each decade as was actually observed in the annual bag records. The model substantiates the supposition that declines in the Danish hare population are caused by reduced juvenile recruitment, and moreover, the model predicts further population decline. Point transect counts are suitable and corrections for detection necessary, when monitoring hare populations, but work is still needed, before the effects of e.g. road avoidance on density estimates are fully clarified. The genetic variation of hares reveals that the population is subdivided and gene flow restricted even between close populations. The genetic differences are caused by a combination of genetic drift, ancient history and translocations. Future research should focus on determining causes of juvenile mortality, and reasons for variation in female fecundity, as well as the genetic consequences of the low densities on the mainland, along with the sustainability of hunting in low-density areas.
Full report in pdf (3.7 MB)
