Graduate Thesis Or Dissertation
 

Behavioral constraints on harlequin duck population recovery from the Exxon Valdez oil spill in Prince William Sound, Alaska

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  • I investigated the relationship between harlequin duck (Histrionicus histrionicus) behavior and lack of recovery from the Exxon Valdez oil spill in Prince William Sound, Alaska. First, I evaluated the hypothesis that harlequin ducks in winter have little flexibility to increase foraging time in response to disturbance because they are constrained to forage during daylight. Eight radio-tagged harlequin ducks wintering in Resurrection Bay, Alaska were monitored for evidence of dive-feeding at night. Each radio-tagged individual was detected during an average of 19.5 of 22 nocturnal monitoring sessions and signal loss indicative of diving behavior was not detected during a total of 780 minutes of signal monitoring. In contrast, the same 8 radio-tagged birds were detected during an average of 9.1 of 12 daytime signal monitoring sessions and signal loss indicated diving behavior during an average of 62 ± 7% of 5-minute daytime monitoring periods (total of 364 minutes of signal monitoring). Thus the harlequin ducks monitored in this study rarely, if ever, fed by diving at night, possibly due to reduced foraging efficiency and (or) increased predation risk at night. This result suggests that harlequin ducks in mid-winter may be severely time-limited in their foraging, especially in northern parts of their winter range. Therefore, subtle changes in energy requirements and (or) time-activity budgets as a result of continued exposure to residual oil from the Exxon Valdez oil spill may affect the ability of harlequin ducks to meet their daily energy requirements. Second, I tested the hypothesis that exposure to crude oil affects time-activity budgets of harlequin ducks. Controlled oil-dosing and plumage-oiling experiments were conducted using adult female harlequin ducks in captivity. I found no evidence that ingestion of weathered Prudhoe Bay crude oil affected the occurrence of feeding activity during 30-minute observation periods, nor was there evidence of effects on time spent feeding. Effects of crude oil ingestion on maintenance activity were detected, but were neither consistent between the 2 years of the study, nor dose-dependent for the 2 doses administered (2 and 20 mL kg⁻¹ wk⁻¹), and therefore did not strongly support an oil-dosing effect on maintenance activity. Consequently, these results provided little support for the hypothesis that oil ingestion affects time-activity budgets of captive harlequin ducks, at least for the doses and conditions of captivity used in this study. Plumage-oiling reduced feeding activity in captive harlequin ducks. The estimated probability of feeding during 30-minute observation periods for birds in the high-exposure oiling group (5 mL of crude oil) was 53% less than that of non-oiled controls. Oiled birds exhibited a trend of reduced time feeding with increasing level of external-oiling; this effect was greatest among birds in the high-exposure oiling group, which spent 43% less time feeding than non-oiled birds. Reduced feeding was associated with less time in the water dive-feeding and presumably lower heat loss. Trends in the occurrence of maintenance activity and time spent in maintenance activity for birds in the high-exposure treatment suggested plumage-oiling increased maintenance activity, but results were not conclusive. The behavioral changes associated with plumage-oiling in captivity would likely reduce fitness in the wild, where a high proportion of time must be spent in the water feeding. If residual Exxon Valdez oil sequestered in beach sediments enters the water column where it may be encountered by harlequin ducks, external exposure may lead to reduced feeding activity. This, in turn, may compromise survival, particularly during mid-winter when the time available for diurnal foraging is low and maintenance energy requirements are high.
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