| Summary: | Predation is difficult to observe and quantification of impacts have consequently been difficult, especially for predators active at night. Using night-capable cameras placed throughout a California least tern (Sternula antillarum browni) colony I examined rates of predation by a complex of potential predators. I identified and quantified direct and indirect effects for each potential predator observed in the colony at night. Small mammals, European starlings (Sturna vulgaris), great horned owls (Bubo virginianus), opossum (Didelphis virginiana), and coyotes (Canis latrans) were observed in the colony. Coyotes were the most frequent potential predator and were observed on 12 nights in each of the two nesting seasons of investigation. Great horned owls, opossum, and coyotes predated on terns at night (n = 34, total from both seasons) and coyotes alone were observed predating more than other species (n = 31, total from both seasons). Predator presence in the tern colony resulted in a mean of 15.5 ± 3 minutes ( ± SE) of temporary nest desertion (n = 41 predator events). Anthropogenic disturbances resulted in a mean of 150 ± 25 minutes of temporary nest desertion (n = 13). The mean number of nests observed during these disturbances was 20.3 ± 1.3 nests and varied with time in the season between 2 – 41 nests. All observable nests flushed during every anthropogenic disturbance, whereas 86 ± 0.02% of observable nests flushed during predator caused disturbances. No association was found between abandoned nests and distance to predated nests in either season. Although coyotes were associated with the greatest number of observed predations, the total number of predations could have been greater if coyotes were not present. Smaller predators such as red fox (Vulpes vulpes), black rats (Rattus rattus), and California ground squirrels (Spermophilus beecheyi) may have greater access to the colony in the absence of coyotes. Thesis (M.S.)--Humboldt State University, Natural Resources: Wildlife, 2008
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