No abstract

Insect harassment significantly affected caribou behavior by decreasing time spent feeding and lying and by increasing locomotion. Effects of oilfield disturbance on behavior were most pronounced when insects were absent, suggesting that disturbance and insects did not have a substantial additive effect on behavior. When insects were absent, caribou within 600 m of an elevated pipeline and road with traffic, and within 300 m of a pipeline and road without traffic, had significantly different activity budgets than undisturbed caribou; disturbance effects were significantly greater in the site with traffic. Time spent lying and running and movement rates were the best indicators of oilfield disturbance, whereas time spent feeding was not affected. Cow–calf-dominated groups and groups larger than 10 animals reacted to lower levels of disturbance than other group types, but all group types reacted similarly to high levels of disturbance. Separation of elevated pipelines from heavily traveled roads is recommended as a means of minimizing disruption of caribou behavior and movements. Energetic stress resulting from disturbance-induced changes in behavior should be minimal in a properly designed oilfield.

We used data from pre-and post-spill surveys to assess the effects of the Exxon Valdez oil spill on the abundance and distribution of birds in Prince William Sound, Alaska. We conducted post-spill surveys during midsummer (1989-1991) in 10 bays that had been surveyed prior to the spill (1984-1985) and that had experienced different levels of initial oiling from the spill (unoiled to heavily oiled). We evaluated whether there were changes in overall abundance across all bays between the pre-spill and post-spill sampling periods, and changes in abundance in unoiled/lightly oiled bays versus moderately/heavily oiled bays that would suggest oiling impacts. Of 12 taxa examined for changes in overall abundance, 7 showed no significant change, 2 (Bald Eagle and Glaucous-winged Gull) increased in abundance, and 3 (Red-necked Grebe, Pelagic Cormorant, and Pigeon Guillemot) decreased in abundance during all three post-spill years. Of the 11 taxa examined for differences in use of oiled versus unoiled habitats, 7 showed no significant response, 1 (Black-legged Kittiwake) exhibited a positive response to oiling, and 3 (Pelagic Cormorant, Black Oystercatcher, and Pigeon Guillemot) exhibited negative responses to initial oiling. We conclude that the impacts of this oil spill on abundance and distribution of birds were most evident in 1989, the year of the spill, and were most pronounced for Pigeon Guillemots. By 1991, signs of recovery were evident for all taxa that showed initial oiling impacts.

No abstract

Evaluations of the ecological consequences of environmental accidents can benefit from a long‐term perspective. To assess the effects of the Exxon Valdez oil spill on habitat use and occupancy during midsummer by marine‐oriented birds over a 12‐yr period following the spill in 1989, we conducted surveys in 10 study bays in Prince William Sound, Alaska, USA. These bays varied from completely unoiled to some of the most heavily oiled locations in the spill zone. We used oiling as a quantitative variable with and without habitat measures as covariates to assess spill effects and their changes over time. We also used oiling as a categorical variable (“oiled” vs. “unoiled” bays) to conduct between‐year, repeated‐measures analyses that used 1984 data as a baseline and to plot abundance trends by oiling category. We combined the results of these analyses in a “weight‐of‐evidence” approach to determine overall impacts and recovery for each species. To assess changes in habitat condition following the oil spill, we also measured several habitat features in 1991, 1998, and 2001. There were significant increases in the proportion of shoreline covered by rockweed (Fucus) and mussels in oiled bays between 1991 and 1998–2001, suggesting recovery of oiled habitats. Of the 25 bird species whose status we evaluated, 12 (48%) exhibited no evidence of any spill impacts, 10 (40%) exhibited negative impacts that subsequently disappeared, and three (12%) exhibited positive relationships with oiling that later disappeared. No species provided clear evidence of any delayed impacts. In comparison with our earlier analysis of a more extensive data set collected from these same study bays during 1989–1991, we detected slightly more initial spill impacts in the present study but also found that several species whose habitat occupancy had not recovered by the end of our earlier study had now recovered. Our conclusions differ from those of some other studies of the effects of the Exxon Valdez oil spill on birds, perhaps because of differences in study design, in the criteria used to assess impact and recovery, and in the definition of “recovery.” These differences illustrate the difficulties of evaluating the consequences of environmental accidents, even in such a dramatic and well‐studied situation as the Exxon Valdez oil spill. Long‐term studies of environmental accidents create a paradox: the long‐term perspective is needed to see how impact and recovery dynamics are played out, yet background natural variation can make it increasingly difficult to detect clear patterns. With the passage of time after an environmental accident, more things happen, making it more difficult to attribute observed patterns to the event alone. Consequently, long‐term assessments of ecological impacts may be restricted to documenting only large effects; the use of α levels greater than the traditional 0.05 can facilitate such analyses and reduce the likelihood of committing type II errors.