. The Canadian field-naturalist. Natural history; Sciences naturelles. with Grant y = 0 0616x - H' • 0 715 \ Without Grant: y 0 0707x - 6 070«, R' « 0 908 100 120 140 160 180 200 220 Breeding Bird Densities (pairs /100 ha) V 10. 25 30 35 40 45 50 Species Richness (all species) 55 FiCiLRE 4. Relationship between (a) mean female cowbird densities and average densities of all other breeding bird species, and (b) mean female cowbird densities and mean species richness within the breeding bird community (excluding cowbirds) in Conser\ation Reserve Program (CRP) grasslands in Nonh Dakota, So
. The Canadian field-naturalist. Natural history; Sciences naturelles. with Grant y = 0 0616x - H' • 0 715 \ Without Grant: y 0 0707x - 6 070«, R' « 0 908 100 120 140 160 180 200 220 Breeding Bird Densities (pairs /100 ha) V 10. 25 30 35 40 45 50 Species Richness (all species) 55 FiCiLRE 4. Relationship between (a) mean female cowbird densities and average densities of all other breeding bird species, and (b) mean female cowbird densities and mean species richness within the breeding bird community (excluding cowbirds) in Conser\ation Reserve Program (CRP) grasslands in Nonh Dakota, South Dakota. Minnesota, and Montana. 199()-2(K)6. The circle in Figure 4a indicates a potential outlier. Grant County in Minnesota, w hich is discussed in the text. our nests fortuitously and observed each nest onl\ once. Any cov\ bird eggs ejected before our sur\ e\ s. an\ nests abandoned before our surveys, any cow bird eggs buried completely in the nest lining, and any cowbird eggs added or remo\ ed after our brief obser\ ations w ere not recorded in our studies, and thus our frequencies of cow bird parasitism should be considered minimal esti- mates. These limitations, however, are not unique to our data but rather are cotnmon features of all studies of cowbird parasitism that do not involve cameras, because most nests are not monitored condnuously throughout the nesting cycle but rather are \isited at relati\eh tixed intervals (, every 2—1- days) for rela- tively brief periods of time (, less than a few min- utes). Even systematic nest searches are neither inces- sant nor comprehensive, but rather occur at fixed intervals ( Koford et al. 2000: Davis 2003: Winter. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Ottawa Field-Naturalists' Club. Ottawa, Ottawa Field-Naturalists' Club
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