As vegetation wakes up earlier and earlier due to climate change, the calving period in deer only shifts slowly. This has an impact on the food available for young people, according to a study by the WSL Institute.
Wild animals give birth to their offspring when environmental conditions guarantee an optimal survival rate. The fawns therefore come into the world at the start of the vegetative period.
The suckling kids then have tender and digestible herbs and herbaceous plants, high in energy and protein, the Federal Institute for Forest, Snow and Landscape Research (WSL) said on Monday in a press release.
As climate change leads to increasingly earlier vegetation development, the period when food is most abundant and that of calving in deer overlap less and less often on the Swiss Plateau, according to this study by Kurt Bollmann, wildlife biologist at WSL.
Ear mark for fawns
In Switzerland, fawns have been marked by ear since 1971, and the place of their discovery is carefully recorded. Maik Rehnus of WSL and Marta Peláez of the Polytechnic University of Madrid compared the calving dates of 8,983 calves from 1971 to 2015 with long-term data for the start of the growing season for their research. and the date of the first haymaking.
Results: the vegetative period begins on average 0.45 days earlier each year and the first haymaking 0.32 days earlier. During the 45 years studied, the start of vegetation was thus shifted by 20 days and haymaking by 14 days, but birthing dates only advanced by three days in total, 0.06 days per year.
At all altitudes, they evolved much more slowly than vegetation, according to this work published in the journal Ecosphere. The slowness of this adaptation could be partly due to the fact that the reproduction of the deer is controlled by the day / night ratio, which obviously does not evolve under the effect of climate change.
The gap is widening
At low altitudes, calving occurs more and more outside the period when food resources are ideal, whereas they are optimal at high altitudes. According to the researchers, the consequences are uncertain.
“Thanks to the relatively small and mosaic management of agricultural crops spread over time, deer find enough food even when conditions are no longer optimal on the prairies”, explains Kurt Bollmann, quoted in the press release.
However, it is possible that deer will become scarce on the Plateau in the future and that it will colonize hilly and mountainous areas more strongly, because the development of vegetation begins later and therefore coincides better with calving.
For deer populations, the impact of this time lag between calving dates and grassland development will depend not only on the management of other crops, but also on weather conditions in winter and during the rearing of the young.
The researchers therefore recommend extending the monitoring of calves and even densifying it at low altitude: “In this way, the evolution of deer populations will be detected in time and the hunting management can be adjusted accordingly”, concludes Maik Rehnus, first author of the study.
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