Red deer (Photo Friedrich Boehringer via Wikimedia Commons)
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First evaluations of hunting statistics (hunting bags, road kill numbers, body weights) from the state of Lower Austria suggest that high population densities of deer are related to a shift in the sex ratio of calves towards females. In particular, high numbers of juvenile female deer in the population and fewer of older female animals seem to contribute to this effect. The age structure of the males in the population also seems to have an effect on the calves' sex ratio. There is a tendency for more male calves in a population the more deer of age class I (completed 10 years of age) are contained in that population.
These findings suggest that excessively high stocks and an unfavorable age and sex structure shift the sex ratio of calves to more female offspring. From long-term studies on Scottish deer, it is known that female animals in good condition - that is, rather dominant, older animals - tend to have male offspring, but this is less and less the case the more dense a stock, i.e the higher the food competition. Furthermore, experimental studies on Spanish deer have shown that the larger the antlers of male deer were, the more male calves were sired. In Lower Austria such capital deer are found mainly in age class I.
We suspect that these characteristics of the reproductive biology of the red deer can actually be demonstrated even in the case of free-living deer in Lower Austria. It is probable that the urgently needed reduction pf the number of deer can be achieved more easily if mangement interventions in different age and sex classes are carried out in such a way that the gender ratio of the increase is shifted in favor of male offspring.
In order to clarify these questions, we are analyzing the long-term hunting statistics from Lower Austria to examine to what extent the population density and/or structure influences the sex ratio in red deer calves.
The birth-sex ratio plays a crucial role in the management of ungulate game species. On the one hand, hunters are interested in maximizing the yield of capital trophy stags, on the other hand it is necessary to limit excessive population growth in order to reduce the risk of wildlife injuries in road traffic and to reduce the spread of wildlife diseases. The latter is particularly true for those species that have experienced considerable population growth in recent years. This includes red deer, where hunting bags have risen sharply in Central Europe over the last decades, which points to growing populations and can cause the above mentioned problems. A sex ratio shift towards male deer calves could not only help to increase the output of trophy stags, but could also reduce deer population growth by lowering the number of female animals in the population.