Search

Grassland birds are often affected negatively by habitat fragmentation. Outcomes include greater nest predation and brood parasitism, decreased colonization rates of small, isolated patches, and greater nest density in remnant core habitats. These effects have been well documented in the Midwest, but little is known about fragmentation and edge effects on grassland birds in the fragmented agricultural fields within the forested landscapes of the northeastern United States. From 2002 to 2010, we assessed how edges and edge types affected nest-site location and daily nest survival (DNS) of Savannah Sparrows {Passerculus sandwichensis) and Bobolinks (Dolichonyx oryzivorus) breeding in 11 fields (range: 13.2-38.3 ha; mean = 21.1 ha) within a large agricultural region of Vermont. Mean (± SD) distance to edge was 80.3 ± 39.6 m for Savannah Sparrows (n = 995) and 94.5 ± 56.5 m for Bobolinks (n = 652). Both species nested significantly less than expected within 50 m of the edge. For Savannah Sparrows nesting within 50 m of the edge, DNS increased with increased distance from the edge. Birds initiating nests later in the season nested closer to edges, but renests were farther from edges than first nests. Distance to edge had no detectable consequence for Bobolink nest success. Both species used portions of fields near hedgerows less than expected but used wetland, forest, agricultural, road, and developed edges in proportion to availability. For both species, DNS did not vary among edge types. Although edges were used less than expected, nesting near edges had only minor consequences for nest success. [ABSTRACT FROM AUTHOR]

In some species, habitat edges (ecotones) affect nest-site selection and nesting success. Openness, or how visually open a habitat is, has recently been shown to influence grassland bird density and may affect nest-site selection, possibly by reducing the risk of predation on adults, nests, or both. Because edge and openness are correlated, it is possible that effects of openness have been overlooked or inappropriately ascribed to edge effects. We tested the roles of edges and visual openness in nest-site selection and nesting success of two grassland passerines, the Bobolink (Dolichonyx oryzivorus) and Savannah Sparrow (Passerculus sandwichensis), in the Champlain Valley, Vermont. We also evaluated the sensitivity of our results to alternative definitions of edge on our landscape. Bobolink (n = 580) and Savannah Sparrow nests (n = 922) were located on seven hay fields and three pastures from 2002 to 2010. Both species avoided placing nests near edges and in less open habitat compared with expectations based on random placement. When the effects of openness and edge were separated, less open habitats were still avoided, but edge responses were less clear. These results were robust to different definitions of habitat edge. We found no strong relationships between either openness or edges and reproductive success (numbers of eggs and fledglings, percentage of eggs producing fledglings, and nest success), although there may be an edgespecific openness effect on timing of reproduction (clutch completion date). Our results support openness as an important factor in nest-site selection by grassland birds. [ABSTRACT FROM AUTHOR]

The article discusses a study on the assessment of a reproductive index for estimating the productivity of grassland breeding birds. The study subjects were Savannah Sparrow birds found in New York. Differences were found between territory and nest success rates calculated using the index and using nest searching and monitoring.

The article investigates the relationship of ambient temperature with immune response in a wild population of Savannah Sparrows Passerculus sandwichensis. Results revealed that phytohemagglutinin (PHA)-induced immune response was not correlated with nestling recruitment rates but is associated though with minimum ambient temperature for males hatched in 2002 and 2003 and for females hatched in 2003. The study also found the correlation of immune response to PHA with nestling mass for males and females during the same period.

The article discusses a study on the dispersal of Dolichonyx oryzivorus and Passerculus sandwichensis, also known as Bobolinks and Savannah Sparrows, respectively, to determine the impact of agricultural management practices on dispersal patterns and habitat selection. The study subjects included adults and nestlings found on hay fields and pastures in the Champlain Valley in the U.S. While differential breeding-dispersal distances were found between male and female Savannah Sparrows, such distances were not found in Bobolinks.

The article presents a study on how hay cropping affects the habitat of the Savannah Sparrows or Paseerculus sandwichensis and the biomass of the invertebrates.It states that the study was made by using treatment hay fields in the Champlain Valley of Vermont in 2004-2005. The article explains that harvesting decreases bird distribution in the area as well as food delivery and suggests that the resulting situation could be compensated by sparrows by devoting more time to gather their provisions.