Artificial Nest Experiments: Effects of Nest Appearance and Type of Predator’

Nest predation is a primary cause of nesting mortality for many bird species (Sk&h 1949, 1966; Nice 1957; Ricklefs 1969: Nilsson 1984). Food limitation and competition also can affect nesting success (see reviews in Martin 1986, 1987). However, the primary role of nest predation in nesting mortality suggests that it can be a strong agent of selection on bird species and assemblages; when nest predation differs among species, habitats, and areas, it can influence life history traits, habitat use, and population and community patterns (Duebbert and Kantrud 1974; Slagsvold 1982; Martin, unpubl.). Intensity of nest predation differs among groups of birds based on the nesting substrates and heights of their nests (Ricklefs 1969, Nilsson 1984) between island and mainland areas (Loiselle and Hoppes 1983, Savidge 1987) and among habitat islands of different sizes (Wilcove 1985). One means of documentina such differences in nest predation is through controlled experiments using artificial nests. Two recent studies (Loiselle and Hoppes 1983, Wilcove 1985) used artificial wicker nests to examine differences in predation rates for different nest types, habitats, and areas. Both studies used wicker nests with leaves or straw lining the inside of the nest and without modification of the outside of the nest (e.g., Loiselle and Hoppes 1983, Wilcove 1985). Wilcove (1985) noted that these nests were more conspicuous than real nests. Consequently, both he and Loiselle and Hoppes (1983) felt that artificial nests did not measure the actual rate of predation that birds experience, but they assumed that any biases were consistent among sites and nest types. However, this crucial assumption requires testing before further experiments are conducted. In this paper, I report results of experiments that test effects of nest appearance and placement on probability of nest predation.