Polar bears are inefficient predators of seabird eggs

Climate-mediated sea-ice loss is disrupting the foraging ecology of polar bears (Ursus maritimus) across much of their range. As a result, there have been increased reports of polar bears foraging on seabird eggs across parts of their range. Given that polar bears have evolved to hunt seals on ice, they may not be efficient predators of seabird eggs. We investigated polar bears\u27 foraging performance on common eider (Somateria mollissima) eggs on Mitivik Island, Nunavut, Canada to test whether bear decision-making heuristics are consistent with expectations of optimal foraging theory. Using aerial-drones, we recorded multiple foraging bouts over 11 days, and found that as clutches were depleted to completion, bears did not exhibit foraging behaviours matched to resource density. As the season progressed, bears visited fewer nests overall, but marginally increased their visitation to nests that were already empty. Bears did not display different movement modes related to nest density, but became less selective in their choice of clutches to consume. Lastly, bears that capitalized on visual cues of flushing eider hens significantly increased the number of clutches they consumed; however, they did not use this strategy consistently or universally. The foraging behaviours exhibited by polar bears in this study suggest they are inefficient predators of seabird eggs, particularly in the context of matching behaviours to resource density

Observation of High-Energy Astrophysical Neutrinos in Three Years of IceCube Data

A search for high-energy neutrinos interacting within the IceCube detector between 2010 and 2012 provided the first evidence for a high-energy neutrino flux of extraterrestrial origin. Results from an analysis using the same methods with a third year (2012-2013) of data from the complete IceCube detector are consistent with the previously reported astrophysical flux in the 100 TeV - PeV range at the level of $10^{-8}\, \mathrm{GeV}\, \mathrm{cm}^{-2}\, \mathrm{s}^{-1}\, \mathrm{sr}^{-1}$ per flavor and reject a purely atmospheric explanation for the combined 3-year data at $5.7 \sigma$. The data are consistent with expectations for equal fluxes of all three neutrino flavors and with isotropic arrival directions, suggesting either numerous or spatially extended sources. The three-year dataset, with a livetime of 988 days, contains a total of 37 neutrino candidate events with deposited energies ranging from 30 to 2000 TeV. The 2000 TeV event is the highest-energy neutrino interaction ever observed.Comment: 8 pages, 5 figures. Accepted by PRL. The event catalog, event displays, and other data tables are included after the final page of the article. Changed from the initial submission to reflect referee comments, expanding the section on atmospheric backgrounds, and fixes offsets of up to 0.9 seconds in reported event times. Address correspondence to: J. Feintzeig, C. Kopper, N. Whitehor

Measurement of atmospheric neutrino oscillations with IceCube

We present the first statistically significant detection of neutrino oscillations in the high-energy regime (>20 GeV) from an analysis of IceCube Neutrino Observatory data collected in 2010 and 2011. This measurement is made possible by the low-energy threshold of the DeepCore detector (~20 GeV) and benefits from the use of the IceCube detector as a veto against cosmic-ray-induced muon background. The oscillation signal was detected within a low-energy muon neutrino sample (20-100 GeV) extracted from data collected by DeepCore. A high-energy muon neutrino sample (100 GeV-10 TeV) was extracted from IceCube data to constrain systematic uncertainties. The disappearance of low-energy upward-going muon neutrinos was observed, and the nonoscillation hypothesis is rejected with more than 5σ significance. In a two-neutrino flavor formalism, our data are best described by the atmospheric neutrino oscillation parameters |Δm(32)(2)|=(2.3(-0.5)(+0.6))×10(-3) eV(2) and sin(2)(2θ(23))>0.93, and maximum mixing is favored.M. G. Aartsen ... G. C. Hill ... et al. (IceCube Collaboration

Measurement of the cosmic ray energy spectrum with IceTop-73

We report on the measurement of the all-particle cosmic ray energy spectrum with the IceTop air shower array in the energy range from 1.58 PeV to 1.26 EeV. The IceTop air shower array is the surface component of the IceCube Neutrino Observatory at the geographical South Pole. The analysis was performed using only information from IceTop. The data used in this work were taken from June 1, 2010 to May 13, 2011. During that period the IceTop array consisted of 73 stations, compared to 81 in its final configuration. The measured spectrum exhibits a clear deviation from a single power law above the knee around 4 PeV and below 1 EeV. We observe spectral hardening around 18 PeV and steepening around 130 PeV.M. G. Aartsen ... G. C. Hill ... et al. (IceCube Collaboration

Polar bear foraging on common eider eggs: estimating the energetic consequences of a climate-mediated behavioural shift

Climate-mediated phenological shifts can cause species to lose access to their primary prey while increasing opportunities for alternative-prey encounters. Species that are able to capitalize on alternative resources could potentially profit from prey-switching should the benefits of procuring these alternative resources outweigh their acquisition costs. Polar bears, Ursus maritimus, use sea ice as a platform to hunt seals, and individuals inhabiting the southern-most extent of their range rely on accumulated fat reserves to sustain themselves during the increasingly lengthy ice-free season. In response to declining access to their primary prey through documented sea ice loss, some polar bears are foraging on the eggs of birds in lieu of hunting opportunities on ice, as their onshore arrival is increasingly overlapping with birds’ breeding schedules. To gain a better understanding of the energetic consequences of this behaviour, we used aerial drones to record polar bears foraging on sea duck eggs (common eider, Somateria mollissima) on Mitivik Island, Nunavut, Canada. Using these data, we examined variation in individual polar bear foraging behaviours and estimated the energetic benefits and costs associated with foraging on common eider eggs. Because of low costs associated with nest searching and consumption, the energetic cost of foraging remained relatively constant throughout the 2-week observation period. However, we found that as the common eider breeding season progressed, polar bears consumed eggs at a lower rate as they depleted the nesting colony and spent proportionally more time searching for nests. Collectively, this foraging pattern led to an overall declining trend in the net energy gained from egg consumption. Foraging on common eider eggs during increasingly lengthy ice-free seasons is apparently beneficial for polar bears, but only during a limited window of opportunity. By coupling energetic estimates with detailed behavioural data collected through aerial videography, this study provides a quantification of both the benefits and costs of egg consumption for polar bears

Polar bears are inefficient predators of seabird eggs

Climate-mediated sea-ice loss is disrupting the foraging ecology of polar bears (Ursus maritimus) across much of their range. As a result, there have been increased reports of polar bears foraging on seabird eggs across parts of their range. Given that polar bears have evolved to hunt seals on ice, they may not be efficient predators of seabird eggs. We investigated polar bears\u27 foraging performance on common eider (Somateria mollissima) eggs on Mitivik Island, Nunavut, Canada to test whether bear decision-making heuristics are consistent with expectations of optimal foraging theory. Using aerial-drones, we recorded multiple foraging bouts over 11 days, and found that as clutches were depleted to completion, bears did not exhibit foraging behaviours matched to resource density. As the season progressed, bears visited fewer nests overall, but marginally increased their visitation to nests that were already empty. Bears did not display different movement modes related to nest density, but became less selective in their choice of clutches to consume. Lastly, bears that capitalized on visual cues of flushing eider hens significantly increased the number of clutches they consumed; however, they did not use this strategy consistently or universally. The foraging behaviours exhibited by polar bears in this study suggest they are inefficient predators of seabird eggs, particularly in the context of matching behaviours to resource density

Predatory cue use in flush responses of a colonial nesting seabird during polar bear foraging

Nest predation is a primary cause of reproductive failure in birds; thus, predators apply strong selective pressure on nesting behaviour, especially risk assessment behaviours during predator encounters at nests. Prey\u27s risk assessments are not static; rather, dynamic risk assessment theory predicts that prey assess risk in real-time and update it according to changes in cues posed by the predator(s). We used drone videography to film nest-flushing behaviours of common eiders, Somateria mollissima, in response to foraging polar bears, Ursus maritimus, on East Bay Island (Nunavut, Canada). We assessed how cue use influenced flushing behaviour and nest fate in a path analysis using 200 observations of 193 eiders in 2017. Our most supported model found that more direct angles of visual gaze and travel angle by polar bears resulted in conspicuous nest flushes by eiders (β = −0.236 ± 0.059), whereas the presence of herring gulls, Larus argentatus, resulted in more discrete flushes of hens walking from their nests (β = −0.181 ± 0.059). Shorter flush initiation distances between eiders and approaching bears resulted in greater nest predation by polar bears (β = −0.203 ± 0.076). We found no support that an eider\u27s visibility from the nest influenced any component of flushing behaviour. We suggest that during encounters with bears, eiders are capable of assessing risk and making appropriate behavioural decisions to reduce the chances of nest loss. However, as the colony experienced heavy predation by bears in 2017, behavioural responses alone appear to be insufficient to mitigate polar bear predation at the population level