European springtime temperature benefits Alpine ibex vitality

Dendrochronology methods applied

An interdisciplinary group of scientists including biologists, climatologists and ecologists from Switzerland, Norway and the US debuts in applying existing methods of tree-ring research (dendrochronology*) to analyze annual horn growth rates of the Alpine ibex (Capra ibex**). For this purpose, climatic drivers of horn growth were disentangled from the effects of animal age and the individual year of harvesting. The findings demonstrate that horn growth is primarily influenced by changes in European springtime temperature. The evaluation of eight ibex populations in the Grison Alps showed that the "North Atlantic Oscillation" (i.e. air masses originating in the North Atlantic) synchronizes annual horn growth rates of male ibex living in different regions and altitudes. Warmer temperatures between March and May result in an earlier snowmelt and overall better food availability. Quality and quantity of alpine grasses and herbs ultimately affect the vitality of the Swiss wildlife icon.

Over 8.000 ibex probed

The team analyzed over 42.000 individual horn increments from more than 8.000 male ibex. This outstanding attempt was enabled by a unique dataset that continuously reaches back to 1964, and resulted from a strictly regulated hunting program of the Department of Wildlife and Fishery Service in Chur. Biological parameter were documented for each animal hunted in October. "Since the Alpine ibex is a highly protected species, it is particularly important to strictly control and document its hunting," explains wildlife biologist Lucie Greuter of the Wildlife and Fishery Department in Chur. More than 20.000 animals were harvested since the revival of the ibex hunt in Grison, where professional gamekeepers consequently measure and digitize each specimen. "The resulting record offers exceptional insight into the relationship between large-scale climate conditions, local trophic interactions, and the animals' overall performance," states Ulf Büntgen, head of this study.

Nevertheless, the authors call attention to the complexity of possible correlations between ibex vitality and climate variability, and emphasize the importance of other factors. Further analyses are necessary to fully understand the complete potential of the ibex dataset in Grison. Kurt Bollmann, wildlife biologist at WSL and co-author of the study, remarks: "Until now, we have not found any conceivable indication that hunting may influence horn growth. Further studies will, however, try to answer if and how hunting can affect the age structure of ibex populations and the horn growth of the individuals."