SUCCESS OF ARTIFICIAL NESTS IN CRP FIELDS, NATIVE VEGETATION, AND FIELD BORDERS IN SOUTHWESTERN MONTANA

In 1993-1994, we used artificial nests to study relationships between nest success and various spatial, temporal, and vegetation variables i n three grassland types: Conservation Reserve Program (CRF) fields, he ld borders and watercourses, and native vegetation. Nest success was h igher and vegetation was structurally more complex in CRP fields than in other grassland types. Nest success was 63% in CRP fields but only 24% in native vegetation. Results of univariate and multivariate analy ses indicated that nests surrounded by taller, thicker cover were more likely to survive than nests with less concealing vegetation. Nests i nitiated later in the season, when vegetation volume was greater, surv ived at higher rates than nests initiated earlier. Spatial variables w ere not strongly related to nest success. Field size was directly rela ted to nest success in CRP fields but not ill other grassland types. H owever, field size was not included in the most parsimonious, multivar iate model of factors related to nest success in CRP fields. Similarly , proximity to field borders was not related to nest success in any gr assland type. Our results suggest that CRP fields, which cover a large area in the Northern Great Plains and attract a greater diversity of grassland birds than the cropfields they replaced, provide secure nest ing cover for ground-nesting species.