Geology topics

George J. Divoky

Publications and source records attributed to George J. Divoky.

4 recordsLinked to original sources

USGS2020

Fatty acid-based diet estimates suggest ringed seal remain the main prey of southern Beaufort Sea polar bears despite recent use of onshore food resources

Polar bears ( Ursus maritimus ) from the southern Beaufort Sea (SB) subpopulation have traditionally fed predominantly upon ice‐seals; however, as the proportion of the subpopulation using onshore habitat has recently increased, foraging on land‐based resources, including remains of subsistence‐harvested bowhead whales ( Balaena mysticetus ) and colonial nesting seabirds has been observed. Adipose tissue samples were collected from this subpopulation during the springs of 2013–2016 and analyzed for fatty acid signatures. Diet estimates were generated for the proportional consumption of ringed seal ( Pusa hispida ), bearded seal ( Erignathus barbatus ), and beluga whale ( Delphinapterus leucas ), relative to onshore foods, including bowhead whale remains and seabird, as represented by black guillemot ( Cepphus grylle mandtii ) nestlings and eggs. Quantitative fatty acid signature analysis (QFASA) estimated that the ice‐obligate prey, ringed seal, remained the predominant prey species of SB polar bears (46.4 ± 1.8%), with much lower consumption of bearded seal (19.6 ± 2.0%), seabird (17.0 ± 1.2%), bowhead whale (15.0 ± 1.4%), and hardly any beluga whale (2.0 ± 0.5%). Adult and subadult females appeared to depend more on the traditional ringed seal prey than adult and subadult males. Diet estimates of SB polar bears showed significant interannual variability for all prey ( F 12, 456 = 3.17, p < .001). Longer‐term estimates suggested that both types of onshore prey, bowhead whale remains and seabird, have represented a moderate proportion of the food resources used by SB polar bears since at least the start of the 21st Century.

Alaska↗

USGS2017

Relative influences of climate change and human activity on the onshore distribution of polar bears

Climate change is altering habitat for many species, leading to shifts in distributions that can increase levels of human-wildlife conflict. To develop effective strategies for minimizing human-wildlife conflict, we must understand the relative influences that climate change and other factors have on wildlife distributions. Polar bears (Ursus maritimus) are increasingly using land during summer and autumn due to sea ice loss, leading to higher incidents of conflict and concerns for human safety. We sought to understand the relative influence of sea ice conditions, onshore habitat characteristics, and human-provisioned food attractants on the distribution and abundance of polar bears while on shore. We also wanted to determine how mitigation measures might reduce human-polar bear conflict associated with an anthropogenic food source. We built a Bayesian hierarchical model based on 14 years of aerial survey data to estimate the weekly number and distribution of polar bears on the coast of northern Alaska in autumn. We then used the model to predict how effective two management options for handling subsistence-harvested whale remains in the community of Kaktovik, Alaska might be. The distribution of bears on shore was most strongly influenced by the presence of whale carcasses and to a lesser extent sea ice and onshore habitat conditions. The numbers of bears on shore were related to sea ice conditions. The two management strategies for handling the whale carcasses reduced the estimated number of bears near Kaktovik by > 75%. By considering multiple factors associated with the onshore distribution and abundance of polar bears we discerned what role human activities played in where bears occur and how successful efforts to manage the whale carcasses might be for reducing human-polar bear conflict.

Alaska↗

USGS2017

Drivers and environmental responses to the changing annual snow cycle of northern Alaska

On the North Slope of Alaska, earlier spring snowmelt and later onset of autumn snow accumulation are tied to atmospheric dynamics and sea ice conditions, and result in environmental responses. Linkages between atmospheric, ecological and biogeochemical variables in the changing Arctic are analyzed using long-term measurements near Utqiaġvik (formerly Barrow), Alaska. Two key variables are the date when snow disappears in spring, as determined primarily by atmospheric dynamics, precipitation, air temperature, winter snow accumulation and cloud cover, as well as the date of onset of snowpack in autumn that is additionally influenced by ocean temperature and sea ice extent. In 2015 and 2016 the snow melted early at Utqiaġvik due mainly to anomalous warmth during May of both years attributed to atmospheric circulation patterns, with 2016 having the record earliest snowmelt. These years are discussed in the context of a 115-year snowmelt record at Utqiaġvik with a trend toward earlier melting since the mid- 1970s (-2.86 days/decade, 1975-2016). At nearby Cooper Island, where a colony of seabirds, Black Guillemots, have been monitored since 1975, timing of egg laying is correlated with Utqiaġvik snowmelt with 2015 and 2016 being the earliest years in the 42-year record. Ice-out at a nearby freshwater lagoon is also correlated with Utqiaġvik snowmelt. The date when snow begins to accumulate in autumn at Utqiaġvik shows a trend towards later dates (+4.6 days/decade, 1975-2016), with 2016 the latest on record. The relationships between the lengthening snow-free season and regional phenology, soil temperatures, fluxes of gases from the tundra, and to regional sea ice conditions are discussed. Better understanding of these interactions is needed to predict the annual snow cycles in the region at seasonal to decadal scales, and to anticipate coupled environmental responses.

Alaska↗

USGS1979

Pomarine jaeger preys on adult black-legged kittiwake

On 5 June 1977, while on a cruise in the decomposing pack ice in the Bering Sea, we observed a light phase Pomarine Jaeger ( Stercorarius pomarinus ) attack, kill and feed on an adult Black-legged Kittiwake ( Rissa tridactyla ), 1 of approximately 10 individuals within 20 m of the ship's stern. We did not observe the birds until 1 min after the initial attack and do not know if the kittiwake was sitting or flying. No food was visible in the kittiwake's bill at the start of our observations nor was it observed regurgitating its stomach contents after the attack. During the first 5 min the kittiwake managed to become airborne a number of times but the jaeger maintained its hold and forced it back to the water. After 5 min the jaeger began to submerge the kittiwake's head, still holding it by the neck. Because of the kittiwake's struggling, the jaeger was unable to hold it under for more than 5 sec at a time. For the next 15 min it continued to submerge the victim's head, lift it out of the water, and then submerge it again. When it held the kittiwake under water, it kept both feet on its lower neck; this may have helped keep the head submerged. In the last 5 min of this activity, when the kittiwake offered little resistance, the jaeger occasionally used only its feet to push it under water. Other kittiwakes remained in the area, a few swimming within 2 m of the 2 birds. No attempt was made to mob the jaeger.

The Wilson Bulletin↗