High survival rates explain 20 years of rapid expansion of wolves in Germany

Young wolves in Germany had an annual survival probability of 75% during the first two decades after the start of German recolonization; for adult wolves it was up to 88 percent. For young wolves up to two years of age, the variation in survival rate depended on the suitability of the habitat – the less suitable it was for the wolves, the lower their survival; for adult wolves, such a relationship could not be established by the scientific team led by the Department of Ecological Dynamics at the Leibniz-IZW. “Using survival analysis, we were able to determine the average survival time of a wolf in Germany to be 146 weeks, which is about three years,” says Prof. Dr. Stephanie Kramer-Schadt, head of department Leibniz-IZW and professor at the University Technique from Berlin. The longest recorded longevity of a wolf in the study data set was nearly 13 years.

“The survival rates of the German wolf population were very high compared to other regions, in fact they were among the highest in the world,” Kramer-Schadt continued. “This indicates that wolves settled in habitats that were very suitable for them during the 20 years we looked at in this paper. Strict legal protection also contributed to high survival rates.” Landscapes that qualify as suitable are those that provide sufficient cover — for example through forest cover — and areas that are as far away from roads as possible. These areas allow wolves to avoid humans and can serve as a refuge for animals. If wolves settle in less suitable habitats, this reduces their survival and reproduction. “While adult animals can still survive and establish territories in less suitable areas, the lower survival rate of young and sub-adult wolves and the smaller number of pups per litter slows population growth and thus the expansion of the species” . Once the optimal areas are occupied, population growth will slow, according to scientists.

The scientific investigation was based on a long-term data set provided by the German Federal Wolf Documentation and Consultation Center (DBBW) and included the surveys and findings of comprehensive wolf monitoring in the German federal states. In addition, it considered the results of tens of thousands of DNA analyzes conducted by the Senckenberg Center for Wildlife Genetics, which made this scientific investigation possible in the first place. The team also determined the reproductive performance of a total of 201 breeding females from 165 territories that were part of the long-term data set analyzed from 2000 to 2020. “We were able to analyze data from those female wolves over the years, who had descendants. — on average for 2.8 years,” says IZW scientist and first author of the paper Dr. Aimara Planillo. “The analyzes also show greater reproductive success of females with more experience and in more diverse habitats suitable, with up to five years of breeding.” In summary, the models show that a suitable habitat and the breeding experience of the female also have a positive effect on the size of the brood, which in Germany has at least four offspring.

Similar scientific analyzes from other countries and regions illustrate how high the survival rate of adult wolves in Germany actually is. Other unhunted populations also have high adult wolf survival rates of 78% in the US or 82% in the alpine regions of central Europe, although these do not come close to Germany’s 88%. The reason for this is that the German population is still growing.

The Department of Ecological Dynamics at Leibniz-IZW investigates (among other things) the population development of large carnivores such as the wolf or the Eurasian lynx using individual-based spatial models from the analysis of past processes – such as the recolonization of Germany. of the wolf — to predict future developments. For the paper recently published in Wildlife Biology, the scientists used demographic data on the wolf population (age, sex, year and place of birth, dates and places of representation, and cause of death) from 2000 to 2020 and were related to environmental variables such as habitat suitability (accounts for different types of land use and the effects of human disturbance, e.g. forested areas, distance to roads or human density), wolf population density (annual density of territories of wolves around the focal territory) and season of the year.

A significant part of the data comes from the ongoing molecular genetic analysis of samples collected in the field, which are sent to Senckenberg as part of the wolf monitoring program in the German federal states. Based on the genetic profiles created, numerous wolf individuals are collected several times over the years and can be assigned to wolf packs by analyzing their relationship. The Leibniz-IZW team then developed spatial-statistical models to determine the influence of environmental variables on population survival probability, annual survival rates of different age classes, reproduction probability and reproductive performance. This revealed how well one variable — such as high habitat quality — can predict each population parameter and how substantial its influence is on the number and spatial distribution of wolves in Germany.

Previous scientific investigations of the Leibniz-IZW have shown that

• the recolonization of Germany by wolves is not a homogeneous, continuous process, but characterized by changing conditions. This means, for example, that wolves show different behaviors in different phases regarding the suitability of habitats: in early phases, wolves liked to “cherry pick” when establishing new territories, while they were much less selective in later phases when the population was close to habitat saturation. The lower survival rate of young animals identified in the current work and the lower number of offspring in less suitable areas offer an explanation for these wolf preferences.
• Germany’s wolf population is essentially healthy and that human-caused deaths such as traffic accidents and illegal killing are responsible for the vast majority of wolves found dead. Data from the 1,000 wolves dissected at Germany’s Leibniz-IZW show that about three-quarters of dead wolves die in traffic collisions — mostly with cars on country roads or highways. In 13.5% of all wolves examined, evidence of a crime, such as illegal gun wounds, was found, although the animals did not always die as a result.

The scientific investigation was funded by the Federal Agency for Nature Conservation (BfN) with funds from the Federal Ministry for the Environment, Nature Conservation, Nuclear Safety and Consumer Protection (BMUV) under grant number 3521 83 1300.