European springtime temperature controls Alpine ibex vitality

Press release WSL: Büntgen et al. (2013) Ecology Letters

Alpine ibex populations benefit from climate change: Warmer springtime temperatures, earlier snowmelt, and hence better food availability enhance their horn growth, which is a sign of overall vitality. An international team headed by Ulf Büntgen and Kurt Bollmann at the Swiss Federal Research Institute WSL present these newly discovered relationships based on a unique dataset from the Department of Wildlife and Fishery Service Grison.

Steinbock Kopie

The horned Alpine ibex excels in climbing (Photo: Claudio Signer)

A study published December 16th, 2013 in the renowned journal “Ecology Letters“, provides new evidence for the dependency of local trophic interactions on large-scale climate dynamics, and reveals positive effects of ongoing climate change for the “Mountain King” of the Alps.

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. Their 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.

The annual ibex horn growth is clearly visible by distinct yearly ring boundaries. The width of the rings may reflect the living conditions of each animal. (Photo: Department of Wildlife and Fishery Service Grison)

The annual ibex horn growth is clearly visible by distinct yearly ring boundaries. The width of the rings may reflect the living conditions of each animal. (Photo: Department of Wildlife and Fishery Service Grison)

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. A wide range of biological parameter was 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 Cantonal Office 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 content of the Grison ibex dataset. 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.”

* Tree-ring research, the so-called dendrochronology (Greek dendron = tree, chronos = time, logos = science), analyzes the individual rings of a tree to ultimately determine its age. The American astronomer A.E. Douglas (1867-1962) introduced the term dendrochronology. Today, it is a well-established method for the age determination in geosciences, archeology, art history, and historic monuments preservation. The sub-disciplines of dendroecology and dendroclimatology aim at reconstructing past conditions of the environment including climate. Comparable to the growth of tree rings, which can reflect some environmental and climatic factors the tree lived in, ibex horns may be an imprint of the specie’s living conditions. While wide rings and long horns reflect optimal living conditions, narrow and short increments are indicative for less suitable circumstances. The Swiss Federal Research Institute WSL in Birmensdorf hosts the world’s leading dendrochronological laboratory.

Having been nearly extinct, the “King of the Mountains” is now one of Switzerland’s most protected animal species. Since 1977, hunting regulates its population. (Photo: Claudio Signer)

Having been nearly extinct, the “King of the Mountains” is now one of Switzerland’s most protected animal species. Since 1977, hunting regulates its population. (Photo: Claudio Signer)

** The Alpine ibex (Capra ibex) belongs to the wild goat family. This hardy horned herbivore, with strong limbs adapted to movement in rocky environment, favors territories with low precipitation above the timber and fog line. Its annual horn growth rates are clearly identifiable. The Alpine ibex has lived through an eventful history. In the Canton of Grison, it was hunted into extinction as early as the 17th century. By the end of the 19th century, the species had disappeared from the whole Alpine region, except for a remnant population of about 100 animals living in the Italian Gran Paradiso area. The resettlement of the Alpine ibex in Switzerland began 1911 and is a story of success. Today, approximately 16.650 Alpine ibex exist in Switzerland, of which 40% live in Grison, where hunting regulates its population since 1977.