Research
Recent BBIRD Research
Results from BBIRD sites in WisconsinFlaspohler et al. (2000). We studied the reproductive ecology of Ovenbirds (Seirurus aurocapillus) for three years in a primarily forested landscape in northern Wisconsin. We searched for and monitored nests in large closed-canopy northern hardwood forests adjacent to recent (< 6 years old) clearcuts, and measured the effect of proximity to edge on nest success, clutch size, and breeding pair density. Mayfield nest success was lower near the forest edge (0.44, Nnests = 42) (< 300 m) relative to the forest interior (0.69, Nnests = 47) (> 300 m) (X2 = 4.43, df = 1, P < 0.04), and mean clutch size was higher (4.93) near the forest edge than in the forest interior (4.27) (t = -3.83,df = 59, P < 0.0003). We found that edge effects on nest success and clutch size extend further (300 m) into intact forest than has been previously documented. Using habitat-specific demographic parameters, we found that annual productivity per pair was similar in edge (3.37 fledglings) and interior (3.85 fledglings) habitat. We used our estimates of per capita annual productivity and published estimates of adult and juvenile survival to approximate the finite rate of growth (l) for birds breeding in edge and interior locations. Based on published estimates of age-specific survival, both edge and interior habitats appear to be source habitats (where l > 1) for Ovenbirds. However, our assessment of population status was extremely sensitive to variation in survival estimates. Ovenbirds near forest edges face higher predation pressure but lay more eggs on average than birds in forest interior habitat, suggesting that Ovenbirds may make tradeoffs between the probability of nest success and the per nest productivity as measured by clutch size.
Flaspohler, D.J., S.A. Temple, and R. Rosenfield. 2000. The effects of forest edges on Ovenbird demography in a managed forest landscape. Talk given at 2000 meeting of the American Ornithologists' Union in St. John's, Newfoundland.
Results from BBIRD sites in MissouriHowell et al. (2000). We examine the influence of both local habitat and landscape variables on avian species abundance at forested study sites situated within fragmented and contiguous landscapes. The study was conducted over a six year period (1991-1996) at 10 study sites equally divided between the heavily forested Missouri Ozarks and forest fragments in central Missouri. We found greater species richness and diversity in the fragments, but there was a higher percentage of Neotropical migrants in the Ozarks. We found significant differences in the mean number of birds detected between the central Missouri fragments and the unfragmented Ozarks for 15 (63%) of 24 focal species. We used stepwise regression to determine which of 12 local vegetation variables and 4 landscape variables (forest cover, core area, edge density, and mean patch size) accounted for the greatest amount of variation in abundance for 24 bird species. Seven species (29%) were most sensitive to local vegetation variables, while 16 species (67%) responded most strongly to one of four landscape variables. Landscape variables are significant predictors of abundance for many bird species; resource managers should consider multiple measures of landscape sensitivity when making bird population management decisions.
Howell, C.A., S.C. Latta, T.M. Donovan, P.A.Porneluzi, G.R. Parks, and J. Faaborg 2000. Landscape effects mediate breeding bird abundance in midwestern forests. Landscape Ecology 15:547-562.
Results from the Bitterroot, MT BBIRD site-
Tewksbury et al. (In Press) documented the effects of landscape level fragmentation on nest predation and brood parasitism in riparian areas of western Montana (Fig 1). Their results demonstrated that the patterns of nest predation were opposite those documented from more eastern studies; predation rates were higher in forested landscapes than in fragmented landscapes dominated by agriculture (Fig 2). They suggest that forest predators (namely red squirrels) are responsible for this trend (Fig 3). Furthermore, the percentage of the local landscape devoted to human habitation (farms, houses, and corrals) was a better predictor of parasitism pressure than the percent of the landscape devoted to agriculture, even though agriculture was much more abundant on the landscape. This suggests that what replaces forest cover may be important in determining parasitism pressure. Parasitism rates also showed a strong positive relationship with the density of hosts on a site. These results suggest that the effects of fragmentation are dependent on the habitat structure, the landscape context, and the predator community.
Tewksbury, Joshua J., Sallie J. Heil, and T. E. Martin. In Press. Habitat fragmentation in a western landscape: breeding productivity does not decline with increasing fragmentation. Ecology.
Results from the Konza Prairie Research Natural Area, KS BBIRD site-
Both periodic fire and grazing have historically been prominent features of the natural ecology of the tallgrass prairie and both continue to be important ecological processes today. Yet, their combined effects on the nesting success of the avian community is poorly understood. Cavitt (In Press) examined the effects of these management practices on the abundance and nesting success of a Brown Thrasher population breeding on the Konza Prairie Research Natural Area of northeastern Kansas. Thrashers were more abundant on sites that were burned and grazed the same year. However, thrashers found on these sites delayed nesting relative to pairs breeding on unburned-grazed, unburned-ungrazed or burned-ungrazed sites. This delay in nest initiation may be costly because of seasonal declines in nestling condition. In addition, the combination of fire and grazing significantly increased nest predation and reduced thrasher nesting success. These results suggest that the combined effects of fire and grazing can influence the reproductive success of avian populations. Furthermore, these results also reaffirm the importance of demographic studies to assess the health of populations.
Cavitt, John F. In Press. Nest predation in a prairie population of Brown Thrashers: Combined effects of fire and grazing. Proceedings of the XVI North American Prairie Conference.
Preliminary results from new BBIRD Grassland/Riparian Sites- Missouri River and Charles M. Russel National Wildlife Refuge, MT
Livestock grazing practices may influence avian community composition and nesting productivity in grassland and riparian habitat types of western North America. Changes in vegetation associated with livestock grazing may directly affect avian community composition by changing the availability of suitable habitat (see figure: left of fence- grazed, right- ungrazed). Grazing may also indirectly affect avian communities by altering quality and amount of vegetation available for nesting. Potential demographic consequences of indirect grazing effects include altered susceptability to mortality or reproductive failure (predation, brood parasitism, extreme weather, etc.).
During the 1998 field season, study sites were selected to represent grazed and ungrazed grassland and riparian habitats. Grassland sites were established on the U. L. Bend NWR (ungrazed) and adjacent BLM, Phillips Resource Area (grazed) lands. Riparian sites were established on the Charles M. Russell NWR (ungrazed) and the Upper Missouri Wild and Scenic River (grazed). Preliminary evaluation of point count data indicate higher species richness on ungrazed sites (grassland: n=33, n=23; riparian: n=58, n=43). A total of 488 nests (grassland: 161 ungrazed,135 grazed; riparian: 120 ungrazed, 72 grazed) were monitored during the 1998 field season. Preliminary evaluation of nest success rates shows a mixed response across species in both habitats. Additional data will be collected during the breeding season of 1999.
Forest bird source populations may be threatened, even in heavily forested landscapes (Results from the southern Indiana BBIRD site)-
Potential source populations of forest-dwelling Neotropical migrant birds may be threatened by anthropogenic changes that increase brood parasitism by Brown-headed Cowbirds (Molothrus ater) and nest predation in heavily forested breeding areas. In south-central Indiana, corridors of agriculture and rural development, ranging from less than 50m to several thousand meters in width, penetrate the interior portions of the heavily forested landscape. These corridors provide habitat for cowbirds and nest predators. We monitored breeding success of 6 species of Neotropical migrants and one resident species near an agricultural corridor and in interior forest. We found that nest survival was lower near the agricultural corridor for most of the species in the nestling stage, but no consistent difference in nest survival was detected during the egg stage. Levels of cowbird parasitism were generally elevated near the agricultural corridor. Estimates of the number of fledglings per nesting attempt indicated that seasonal productivity was lower near the agricultural corridor for 6 of the 7 species. The status of these populations of birds in south-central Indiana as a source in the Midwest may be compromised by extensive intrusion of agricultural corridors within this contiguous, heavily forested landscape.
Ford, T.B., D. Winslow, D. Whitehead, and M. Koukol. In Press. Reproductive success of forest-dependent songbirds near an agricultural corridor in south-central Indiana. Auk.
If you would like to see your current BBIRD results posted please submit a summary, Fig, and citation to the data manager (Alina Niklison).
