Table 1. Derivations of variables used in Poisson regression models, correlation analysis, and detection probability modeling of male Savannah Sparrow and male Bobolink abundance. Point counts were conducted from May 21 to July 2, 2002 in agricultural fields in the Champlain Valley of Vermont and New York.

HABITATSAVS: the sum of the proportions of the landscape within 500 m of the
survey stations in each of the following grassland types: pastures, alfalfa, grass and mixed grass/alfalfa hayfields, fallow fields, and old fields.

HABITATBOBO: the sum of the proportions of the landscape within 500 m of the
point count stations in each of the following grassland types: pastures, grass and mixed grass/alfalfa hayfields, and old fields.

PROPOPEN500: the sum of the proportions of the landscape within 500 m that is not forested
or developed based on digitized maps.

WOODEDEDGEDENSITY500: edge density of forest cover within 500 m, serving as an
indication of the "brokenness" of the landscape based on digitized maps.

PROPOPEN2500: the sum of the proportions of the landscape within 2500 m that is not
forested or developed, based on the LCLU data set.

WOODEDEDGEDENSITY2500: edge density of forest cover within 2500 m, serving as an
indication of the "brokenness" of the landscape, based on LCLU data set.

LEGUME: the percent cover of the alfalfa, trefoil, and clover.

FORB: the percent cover of forbs, including dandelions (excluding legumes).

LITTERDEPTH: vertical depth of litter.

AREA: the size of the field in hectares (see text for field size definition).

WOODEDPERIMETER: the proportion of AREA that is bordered by trees (see text for details).

DAYSSINCECUT: the number of days since the field was mowed, or the number of days
since May 1, 2002 if the field was uncut.

NUMBERCUTS: the number of cuts performed on the field during the study period; serves
as an indicator of management intensity on the field.

CUT: a categorical variable describing whether a field had been cut in the previous 2 weeks; used in removal analyses.

VEGHEIGHT: mean height of vegetation in the survey area on a given count; used in removal analyses.

FIELDPERIMETER: the perimeter of the field in which the survey point was located (meters); used in removal analyses.