Date of Award:
Doctor of Philosophy (PhD)
Barrie K. Gilbert
The primary goals of this research were to investigate 3 ecological factors influencing black bear (Ursus americanus) foraging behavior on an Alaskan salmon (Oncorhynchus spp.) stream: fish availability, social dynamics, and human activity. Over 900 observation hours were Jogged at 2 falls from July !-September I 1993-1995; the lower falls were open to public for wildlife viewing, but the upper falls were restricted to research personnel.
In general, black bears responded to differences in fish accessibility on both spatial and temporal scales. All years of the study, 3 indices of bear activity (bear minutes, bear numbers, bout duration) and fish capture rates were significantly higher (all Ps <0 I 0) at the upper falls where fishing opportunities were more abundant. Furthermore, seasonal variation in black bear density was indicative of fluctuations in fish accessibility: bear numbers were highest midseason when fish appeared more abundant, but decreased towards the end of the summer.
Although many bears fished within 3 to 5 m of one another, the majority of intraspecific interactions (65-75%) were benign as opposed to agonistic with a preponderance of "passive deferrals" where bears detoured around rather than confronted conspecifics. Only 5. 7% of all interactions resulted in reversals or circularity, providing some evidence for a linear dominance hierarchy. The most dominant bears fished where salmon were highly accessible for longer periods of time, therefore capturing more fish than subordinates each year. Of interspecific interactions, black bears were more likely to be displaced when encountering brown bears on the same side rather than opposite sides of the creek.
Of 24 recognized bears, 71% were observed from 75-100% of the time at the upper falls; only 8% (2 females) fished solely at the lower falls. Five of 8 bears that fished exclusively at the upper falls (all large males) appeared wary of researchers upon their arrival. Based on quantile regression analyses, we found that visitor numbers acted as a ceiling on fishing duration of black bears at the lower falls in 1994 and 1995. Furthermore, 2 habituated bears seen frequently at the lower falls spent less time in view (maximum values) as visitor group size increased.
Chi, Danielle K., "The Effects of Salmon Availability, Social Dynamics, and People on Black Bear (Ursus Americanus) Fishing Behavior on an Alaskan Salmon Stream" (1999). All Graduate Theses and Dissertations. 4242.
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