The impact of weather and the phase of the rodent cycle on breeding populations of waterbirds in Finnish Lapland

Climate change may affect bird populations both directly by changing the weather conditions, and indirectly through changes in the food chain. While both theoretical and empirical studies have shown climate change having drastic impacts on polar areas, its consequences on Arctic bird species are still poorly known. Here we investigated how weather and changes in predator–prey interactions affected the annual growth rates of sub-Arctic birds by monitoring the breeding numbers of three duck and seven wader species in the alpine tundra of Finnish Lapland during 2005–2015 (except for 2006). We hypothesized that growth rates of waterbirds would be positively associated with warm and dry weather due to improved reproductive success. Furthermore, we tested the hypothesis that waterbirds have a higher reproductive success during the cyclic rodent peaks, when predators mainly prey on rodents, than during the decline and low phases of the cycle, when predation pressure towards waterbirds increases. Results showed that population growth rates of breeding ducks were negatively associated with the sum of rainfall in the previous year. In waders, growth rates were positively associated with the phase of the rodent cycle in the same year. Our results emphasize the importance of monitoring Arctic bird populations on their breeding areas to explore what the consequences of climate change might be for breeding waterbirds by linking the effects of both weather and rodent abundance.