Large-scale climate variability and rodent abundance modulates recruitment rates in Willow Ptarmigan (Lagopus lagopus)

Abstract

Recruitment of juveniles is important for the size of the next year's breeding population in many bird species. Climate variability and predation may affect recruitment rates, and when these factors are spatially correlated, recruitment rates in spatially separated populations of a species may be synchronized. We used production data from an extensive survey of Willow Ptarmigan from 2000 to 2011 to investigate spatial synchrony in recruitment of juveniles within and among mountain region populations. In addition, we assessed the effects of predation and large-as well as local-scale climate on recruitment of juveniles. Recruitment was synchronized both within and among mountain regions, but the mean spatial correlation was strongest among mountain regions. This may be caused by small-scale factors such as predation or habitat structure, or be a result of sampling variation, which may be large at small spatial scales. The strong synchrony suggests that populations are subject to similar environmental forces. We used mixed effect models at the survey area and mountain region scales to assess the effect of rodent abundance (a proxy for predation rates) and local and regional climate during the breeding season on the recruitment of juvenile birds. Model selection based on AICc revealed that the most parsimonious models at both spatial scales included positive effects of rodent abundance and the North Atlantic oscillation during May, June and July (NAO MJJ ). The NAO MJJ index was positively related to temperature and precipitation during the pre-incubation period; temperature during the incubation period and positive NAO MJJ values accelerate plant growth. A comparison of the relative effects of NAO MJJ and rodent abundance showed that variation in NAO MJJ had greatest impact on the recruitment of juveniles. This suggests that the climate effect was stronger than the effect of rodent abundance in our study populations. This is in contrast to previous studies on Willow Ptarmigan, but may be explained by the collapse in rodent cycles since the 1990s. If Willow Ptarmigan dynamics in the past were linked to the rodent cycle through a shared predator regime, this link may have been weakened when rodent cycles became more irregular, resulting in a more pronounced effect of environmental perturbation on the dynamics of ptarmigan.

Quantifying risk of overharvest when implementation is uncertain

“…com). Based on these data, number of chicks per female (hereafter "production") was estimated using generalised linear models (GLMs) assuming a binomial error structure, following the procedure outlined in Kvasnes, Pedersen, Storaas, and Nilsen (2014).…”

The alternative prey hypothesis revisited: Still valid for willow ptarmigan population dynamics

“…Based on this, and observed effects on ptarmigan habitat occupancy patterns, Henden et al [ 31 ] concluded that factors other than changing rodent population dynamics may be responsible for the declining trend in Scandinavian ptarmigan. Then again, Kvasnes et al [ 32 ] observed a pronounced large-scale spatiotemporal synchrony in ptarmigan recruitment that corresponded with variation in rodent abundance. However, an effect of spring/summer climate (North Atlantic Oscillation, NAO-index, in May, June and July) had a stronger effect on recruitment of ptarmigan than rodents.…”

“…However, an effect of spring/summer climate (North Atlantic Oscillation, NAO-index, in May, June and July) had a stronger effect on recruitment of ptarmigan than rodents. Based on these results, Kvasnes et al [ 32 ] concluded that the link between rodent and ptarmigan dynamics had been weakened following the collapse of rodent cycles during the 1990s, and that climate changes lead to desynchronization.…”

Research advances of Galliformes since 1990 and future prospects

“…Chávez-león et al 2004;Dzialak et al 2011;Anich et al 2013) and climate change (e.g. Kvasnes et al 2014). The home range or territory of the Galliformes and the influence factors, including habitat characteristics, were also interested by many researchers at the early stage (e.g.…”

“…Dzialak et al 2012;Ross et al 2016), and their results showed that the habitat use patterns of some species varied at different spatial scales (Dzialak et al 2012), whereas those of some species were similar at different spatial scales (Thogmartin 1999). As regards the temporal scale, researchers conducted these studies at different time intervals, including different seasons, life history stages or years under the background of climate changes, which further influenced the perception of habitat availability and habitat selection (Jones 2001;Dzialak et al 2011;Kvasnes et al 2014).…”