Predation risks for nesting birds in fragmented coast redwood forest

Loss and fragmentation of habitat remain the principal threats to most temperate zone birds in the United States. The coast redwood (Sequoia sempivirens) forest ecosystem has been highly fragmented. The purpose of this study was to evaluate predation risk in relation to nest type, distance from the forest edge, edge type, and nest concealment. The study was conducted in old-growth and mature second-growth coast redwood forest stands in northern California from May to August 1997. Forty-one transects were established extending from the edge to 150 m into the forest interior surrounded by 5 edge types: suburb, young forest, prairie, river, and road. A total of 562 artificial nests (half arboreal nests and half ground nests) with quail eggs were placed at 25-m intervals along the transects and were checked after 7 and 13 days. The probability of predation decreased with increasing distance from the edge, was higher for arboreal nests than ground nests, and was higher later in the nesting season (P < 0.05 for all comparisons). Predation was significantly higher for prairie edge than all other edge types after 7 days (P < 0.05), and was significantly higher than suburb edge after 14 days (P < 0.05). We failed to detect an effect of nest concealment on the risk of predation after 7 days (P = 0.588) and 14 days (P = 0.052). The probability of predation as a function of distance from the forest edge did not indicate a threshold pattern, but rather a gradual decline so that a distance of 115 meters from the edge was required before the probability of predation declined by halt Based on this study we recommend that edge effects be taken into consideration when planning for the conservation of bird species in old-growth and nature second-growth coast redwood forests.