Early end of embryonic diapause and overall reproductive activity in roe deer populations from Bavaria

Context According to the established, older literature, the embryonic diapause (ED) in roe deer ends in late December. In many other species groups, phenological phases are shifting as a result of climatic changes. Whether this is the case in roe deer for the period of ED has not yet been explicitly investigated.Aim The aim of this study was to obtain an up-to-date overview of the reproduction of roe deer in Bavaria, particularly with regard to climate change.Methods For this purpose, uterus samples were taken from roe deer aged at least 1year between September and January and examined macroscopically. The samples were collected during regular hunting activities in Bavaria in the years 2017–2020.Key results A large proportion of the female roe deer examined was found to have been already engaged in reproduction. In 98% of the animals, Corpora lutea (CL) were present in the ovaries. Adult does had significantly more CL than did subadult does just reaching sexual maturity. In 75 roe deer does, 128 embryos, in total, were detected. On average, 1.67 embryos were found per doe with visible embryos. Of these does, 30% carried a single embryo, 67% were bearing twins and 3% were bearing triplets. The animals with visible embryos ranged in age from 1 to 12years. In a few cases, ED was already completed in November or early December. By the end of the hunting season, a correspondingly wide variety of developmental stages of embryos was visible. Our study suggests potential indications that older animals or those with a higher body mass end ED earlier.Conclusions Overall, the results indicated vigorous reproductive activity in the study area. The results showed that some individuals already end the ED in November or early December, so they may adapt to an earlier onset of the vegetation period. In contrast, we found a few individuals that ended the ED during January, which illustrates the temporal range of the ED.Implications Whether the early end of diapause in these roe deer is a reaction to climatic changes or whether there are other underlying causes is something that requires further investigation.