Arctic breeding songbirds cope with variability in the timing of spring onset
The Arctic has been warming at a rate almost three times higher than the global average, and the physical and biological responses are proving acute. Many studies have focused on shifting seasonality in environmental conditions, snow cover and vegetation phenology. Far fewer have examined how the phenology of Arctic fauna - primarily the timing of migration and breeding - have responded, nor what the consequences are for reproductive success. We examine how the timing of spring snowmelt in arctic tundra influences the arrival biology, timing of breeding, availability of critical arthropod food resources, and reproductive success of two species of long-distance migratory songbird (Lapland longspurs and White-crowned sparrows). We compare songbird phenology across three consecutive breeding seasons that differed significantly in their spring environmental conditions via field surveys conducted near the Toolik Lake Arctic Long Term Research Station (ARC LTER) in the northern foothills of the Brooks Range, Alaska (68°38’N and 149°43’W, 760 m a.s.l.).
We found that spring snow cover was different across three years of the study (2012 - 2014). Both songbird species arrived on the north slope of Alaska 6-9 days later in 2013 than in the other years. Body condition (lower fat, muscle and hematocrit values) varied across years in complex ways, and exhibited elevated adrenocortical responses to a standardized acute stressor. Timing of actual onset of breeding varied by less than a week across years, and chicks hatched in concert with the pulse in arthropod biomass from sweep net samples. Fledgling health and reproductive success across years and in relation to environmental conditions will be discussed. Although these results suggest that Arctic breeding Lapland longspurs and White-crowned sparrows are able to cope with significant variation in the timing of spring onset, it remains unknown whether they have the phenotypic plasticity to cope with more extreme shifts in seasonality that are expected with continued arctic warming.