Svalbard rock ptarmigan

Last updated 13 December 2024

The Svalbard rock ptarmigan (Lagopus muta hyperborea) is a subspecies of rock ptarmigan and is the only resident herbivorous bird species in Svalbard. It is endemic to Svalbard in Norway and Franz Josef Land in Russia, making it a species for which Norway has special management responsibilities. Svalbard rock ptarmigan are found in small, relatively stable to increasing populations in very restricted breeding habitats. Knowledge of trends in population size is necessary for their management and rapid climate change requires such trends to be closely monitored.

Status and trend

In 2000, monitoring of Svalbard rock ptarmigan using standardised methods was begun, in order to measure the density of territorial males in the breeding grounds in the study area covering some 1,200 km² in central Spitsbergen (Nordenskiöld Land; Pedersen et al. 2012, Soininen et al. 2016). This monitoring provides a basis for estimating the density of territorial males and thereby the year’s breeding population. Monitoring has shown that, from 2000 to 2013, the number of territorial males was relatively low, with moderate annual variations (from 1 to 3 males per square kilometre; Pedersen et al. 2012, Soininen et al. 2016). Since 2014, there has been a rising trend in the density of territorial males in the monitoring area, which, in the most recent period, has varied between 3 and 5 males per square kilometre (Soininen et al. 2016; Fuglei et al. 2020; Marolla et al. 2021).

Causal factors

The dynamics of the monitoring data from 2000 to 2013 were partly driven by inter-annual variations in rain-on-snow events that synchronized the ptarmigan’s population dynamics with the populations of Svalbard reindeer and sibling voles (Hansen et al. 2013).

Limited access to good ptarmigan habitats with less than 4% of the land areas, and with relatively low carrying capacity in the form of important grazing plants probably makes the Svalbard rock ptarmigan sensitive to changes in plant production. This applies to both the quantity of plants and phenological developments such as nutritional quality. As soon as the ptarmigan chicks emerge from the egg, they have a very specialized diet, consisting of the bulbills of the Alpine bistort plant. This specialization can lead to a so-called phenological mismatch between the times of the ptarmigan’s reproduction and the growth and quality of the grazing plants, if the plants develop earlier due to an earlier start to spring/summer.

The impact of climate change on Svalbard rock ptarmigan can be expected to be both direct and indirect. One direct effect is expected to be changes in the frequency of rain-on-snow events. This effect has already been shown to reduce the population’s growth rate (Hansen et al. 2013). In addition, the climate can have a direct effect on the time of egg-laying, as well as the growth and survival of chicks in the spring.

The indirect effects can occur through changes in interactions with grazing plants and predators.

A warmer climate may also increase primary production (the biomass of grazing plants), which may have a positive effect on the ptarmigan population. Predation of Svalbard rock ptarmigan may increase if the Arctic fox population increases due to a warmer climate. This may occur as a result of an increasing density of geese and reindeer, or greater winter mortality of reindeer.

Since 2014, the population trend of Svalbard rock ptarmigan has been increasing, with considerable variation between years. Marolla et al. (2021) translated the conceptual food web model of COAT (Climate-Ecological Observatory for Arctic Tundra) for Svalbard rock ptarmigan into statistically descriptive models to obtain estimates of the different relationships between the species in the food web and the effects of drivers such as hunting and climate on population dynamics (i.e. changes in density from year to year). Several of the effects were relatively weak, such as a negative effect of harvesting (i.e. the number of birds shot), the amount of precipitation in July, which can affect chick survival, when winter starts (shorter season of snow), and the quantity of reindeer carcasses, which is believed to have an indirect effect through predation from Arctic foxes.

The largest and clearly significant estimate in the model were a positive effect of winter temperature. The effect of winter temperatures, is related to a greatly increased winter temperature over recent years in Svalbard. Warmer winters with extreme mild weather events can also, for example, reduce the effects of rain-on-snow events, because the ice on the ground melts and facilitates access to the grazing plants. Higher winter temperatures probably also lower metabolic costs, and thus enable an increase in winter survival among the Svalbard rock ptarmigan population.

For the time being, it appears that rising average winter temperatures have a strong positive effect on the growth rate of the Svalbard rock ptarmigan population, which outweighs the negative impact from other climate-related changes, such as rain-on-snow events. It also seems as the ptarmigan population can compensate for the current harvesting level (Marolla et al. 2021).

Consequences

The Svalbard rock ptarmigan may be vulnerable for climate changes if they are exposed to a mismatch between the phenological development of their grazing plant, alpine bistort, and the timing of the hatching of their chicks.

Predation pressure from the Arctic fox depends on the development in the geese and reindeer populations. This is related to the climate. We have shown that the winter climate in Svalbard, with periods of mild weather in winter with precipitation as rain, synchronises the entire community of herbivores in Svalbard – ptarmigan, reindeer and sibling vole. Vegetation covered with ice results in higher mortality and poorer production of offspring, due to less food being available. The reduction in the populations of the three herbivores is perfectly synchronised and coincides with the rainy winters.

The results of the model analyses show that there are many factors that influence the population development of Svalbard rock ptarmigan (Marolla et al. 2021). These may include the negative effects of heavy precipitation in the summer and increasing access to reindeer carcasses in winter. Many of the effect estimates are admittedly weak and currently uncertain (not statistically significant). The analysis results must be assessed in the context that climate change is so far quite moderate compared to the expectations for the relatively near future. Today’s models are not able to predict the effect of these future changes.

About the monitoring

The Svalbard ptarmigan is a ptarmigan subspecies and is the only herbivorous bird species that lives in Svalbard year-round. It is endemic to Svalbard and Franz Josef Land, making it a species for which Norway has special management responsibility.

There is low genetic diversity among Svalbard ptarmigan, which indicates that they have been isolated in the archipelago for a long time. Habitats vary throughout the year and the ptarmigan live in distinct areas during the breeding season and in the winter months. Access to suitable breeding habitats may therefore be a limiting factor for the population, since < 4% of the ice-free land areas in Svalbard constitute medium to good habitats for the ptarmigan (Pedersen et al. 2011; 2017).

The Svalbard ptarmigan is hunted annually and is the most harvested game species in Svalbard. Between 500–2,000 ptarmigan are taken per year in central parts of Spitsbergen and in the hunting areas north of Spitsbergen.

Information on the population density of cocks in the spring is important to allow the Governor of Svalbard to regulate the hunt when required. With today’s rapid climate change, knowledge of the size and development of the population over time is important for ensuring sustainable harvesting levels in a new climate.

Because Arctic foxes are the most important ptarmigan predator, and increasing predation can occur as a result of more reindeer carcasses, the management of both Arctic foxes and Svalbard reindeer must be assessed in the context of the development of the Svalbard ptarmigan population.