Trophic matches and mismatches: can polar bears reduce the abundance of nesting snow geese in western Hudson Bay?

Abstract

Climate change driven advances in the date of sea ice breakup will increasingly lead to a loss of spring polar bear foraging opportunities on ringed seal pups creating a phenological trophic ' mismatch ' . However, the same shift will lead to a new ' match ' between polar bears and ground nesting birds. Th is new match will be especially prevalent along the Cape Churchill Peninsula of western Hudson Bay where both polar bears and nesting snow geese are abundant. Easily foraged goose eggs will provide at least some of the earlier arriving polar bears with compensation for the energy defi cit accrued through lost seal hunting opportunities. We examine the potential impact of changes in the extent and pattern of polar bear egg predation on snow goose abundance using projection models that account not only for increases in the temporal overlap of the two species but also for autocorrelation and stochasticity in the processes underlying polar bear onshore arrival and snow goose incubation. Egg predation will reduce reproductive output of the nesting lesser snow geese and, under all but trivial rates, will lead to a reduction in the size of their nesting population on the Cape Churchill Peninsula. Stochasticity associated with the asymmetrical advances in polar bear onshore arrival and the snow goose incubation period will lead to periodic mismatches in their overlap. Th ese, in turn, will allow snow goose abundance to increase periodically. Climate driven changes in trophic matches and mismatches may reduce snow goose numbers but will not eliminate this over-abundant species that poses a threat to Arctic landscapes.

The diet of polar bears (Ursus maritimus) from Svalbard, Norway, inferred from scat analysis

“…The low number of scats containing eggs is likely due to the fact that most scats were collected outside the nesting period of birds in Svalbard. Recent studies have, however, reported increased predation by polar bears on nests of various ground-nesting birds (Stempniewicz 2006;Drent and Prop 2008;Rockwell and Gormezano 2009;Smith et al 2010), which in some cases are interpreted as an effect of climate change since more bears are being stranded on shore for longer periods with declining seasonal extent of sea ice in many parts of the Arctic in recent years (Rockwell et al 2011). …”

Climate change, phenology, and habitat degradation: drivers of gosling body condition and juvenile survival in lesser snow geese

“…Since nutrient content of forage decreases rapidly over the course of the growth season, geese that hatch early generally benefit from high nutrient availability in new forage (Sedinger and Raveling ; Cooch et al ., ; Sedinger & Flint, ). Over the past four decades, snow geese at LPB have advanced their date of hatch at a rate of 0.16 days per year (Rockwell et al ., ), perhaps in an attempt to track the phenology of preferred plant species. Future research will evaluate the extent to which phenology of preferred forage species can explain gosling growth responses and gauge how climate change will affect goslings via changes in plant phenology.…”

Can polar bears use terrestrial foods to offset lost ice‐based hunting opportunities?

“…2007), and the localized, catastrophic effect on bird populations (Smith et al . 2010; Rockwell et al . 2011; Iverson et al .…”