Population declines of cold adapted bird species are caused by mechanisms involving reproduction and survival

The populations of many cold adapted bird species have been declining in the last centuries because of global warming. Many high arctic or mountain species declined or even retreated from southern or low-elevation areas. Knowing the mechanisms that lead to the observed declines helps developing measure to support the populations. We studied how changes in the environment affect the reproduction and survival of a high-elevation bird species, the white-winged snowfinch Montifringilla nivalis.

In central and eastern Alps, we monitored breeding success by measuring nestling growth rate and fledgling weight. We further estimated annual apparent survival for first year and adult birds based on long-term mark-recapture data.

We showed that nestling growth, fledgling weight and first year survival is decreasing with climate warming induced advances of snowmelt. We further found a strong negative correlation between summer temperature and annual apparent survival in adult birds, particularly in females. Summer temperature negatively affected apparent survival during the subsequent winter.

The population dynamics of the white-winged snowfinch is affected by global warming through a phenological mismatch. Breeding phenology of snowfinches does not advance in parallel to the advancing snowmelt. Consequently, the time when the brood needs most energy, the nestling period, does no longer match the time period of highest food availability, i.e. the peak abundance of insect larvae, which develop in the meltwater of the snow. This mismatch leads to lowered first year survival. In addition, warm summer temperatures exhibit a negative carry-over effect on winter apparent survival of adults, particularly in the females. Some alpine plants produce less seeds in warm and dry summers, which may lead to food shortage in the subsequent winter. Food shortage may affect  to a higher degree the smaller, less competitive individuals, i.e. the females. 

An adaptation of the species to a warmer world may only be possible if habitats providing food such as flower-rich alpine meadows can be preserved. Specifically, alpine meadows at cooler and humid locations such as northern slopes, where the snow melts late, may become particularly important.