Variable descriptions:
RT. NO. = Breeding bird survey route number.
RT. NAME = Breeding bird survey route name.
RT. LENG. = Breeding bird survey length in meters.
State = U.S. State.
NLCD 0 = No Data.
NLCD 11 = Open Water - areas of open water, generally with less than 25% cover of vegetation or soil.
NLCD 12 = Perennial Ice/Snow - areas characterized by a perennial cover of ice and/or snow, generally greater than 25% of total cover.
NLCD 21 = Developed, Open Space - areas with a mixture of some constructed materials, but mostly vegetation in the form of lawn grasses.  Impervious surfaces account for less than 20% of total cover. These areas most commonly include large-lot single-family housing units, parks, golf courses, and vegetation planted in developed settings for recreation, erosion control, or aesthetic purposes.
NLCD 22 = Developed, Low Intensity - areas with a mixture of constructed materials and vegetation. Impervious surfaces account for 20% to 49% percent of total cover.  These areas most commonly include single-family housing units.
NLCD 23 = Developed, Medium Intensity – areas with a mixture of constructed materials and vegetation. Impervious surfaces account for 50% to 79% of the total cover.  These areas most commonly include single-family housing units.
NLCD 24 = Developed High Intensity -highly developed areas where people reside or work in high numbers.  Examples include apartment complexes, row houses and commercial/industrial. Impervious surfaces account for 80% to 100% of the total cover.
NLCD 31 = Barren Land (Rock/Sand/Clay) - areas of bedrock, desert pavement, scarps, talus, slides, volcanic material, glacial debris, sand dunes, strip mines, gravel pits and other accumulations of earthen material.  Generally, vegetation accounts for less than 15% of total cover.
NLCD 41 = Deciduous Forest - areas dominated by trees generally greater than 5 meters tall, and greater than 20% of total vegetation cover.  More than 75% of the tree species shed foliage simultaneously in response to seasonal change.
NLCD 42 = Evergreen Forest - areas dominated by trees generally greater than 5 meters tall, and greater than 20% of total vegetation cover.  More than 75% of the tree species maintain their leaves all 2012. Canopy is never without green foliage.
NLCD 43 = Mixed Forest - areas dominated by trees generally greater than 5 meters tall, and greater than 20% of total vegetation cover.  Neither deciduous nor evergreen species are greater than 75% of total tree cover.
NLCD 52 = Shrub/Scrub - areas dominated by shrubs; less than 5 meters tall with shrub canopy typically greater than 20% of total vegetation.  This class includes true shrubs, young trees in an early successional stage or trees stunted from environmental conditions.
NLCD 71 = Grassland/Herbaceous - areas dominated by gramanoid or herbaceous vegetation, generally greater than 80% of total vegetation.  These areas are not subject to intensive management such as tilling, but can be utilized for grazing.
NLCD 81 = Pasture/Hay – areas of grasses, legumes, or grass-legume mixtures planted for livestock grazing or the production of seed or hay crops, typically on a perennial cycle.  Pasture/hay vegetation accounts for greater than 20% of total vegetation.
NLCD 82 = Cultivated Crops – areas used for the production of annual crops, such as corn, soybeans, vegetables, tobacco, and cotton, and also perennial woody crops such as orchards and vineyards.  Crop vegetation accounts for greater than 20% of total vegetation. This class also includes all land being actively tilled.
NLCD 90 = Woody Wetlands - areas where forest or shrubland vegetation accounts for greater than 20% of vegetative cover and the soil or substrate is periodically saturated with or covered with water.
NLCD 95 = Emergent Herbaceous Wetlands - Areas where perennial herbaceous vegetation accounts for greater than 80% of vegetative cover and the soil or substrate is periodically saturated with or covered with water.
BCR = Bird Conservation Region
BCR 5 = Northern Pacific Rainforest.
BCR 9 = Great Basin.
BCR 11 = Prairie Potholes.
BCR 12 = Boreal Hardwood Transition.
BCR 13 = Lower Great Lakes/St. Lawrence Plain.
BCR 14 = Atlantic Northern Forests.
BCR 15 = Sierra Nevada.
BCR 16 = Southern Rockies Colorado Plateau.
BCR 17 = Badlands and Prairies.
BCR 18 = Shortgrass Prairie.
BCR 19 = Central Mixed Grass Prairie.
BCR 20 = Edwards Plateau.
BCR 21 = Oaks and Prairies.
BCR 22 = Eastern Tallgrass Prairie
BCR 23 = Prairie Hardwood Transition.
BCR 24 = Central Hardwoods.
BCR 25 = West Gulf Coastal Plain/Ouchitas.
BCR 26 = Mississippi Alluvial Valley.
BCR 27 = Southeastern Coastal Plain.
BCR 28 = Appalachian Mountains.
BCR 29 = Piedmont.
BCR 30 = New England/MidAtlantic Coasts.
BCR 31 = Peninsular Florida.
BCR 32 = Coastal California.
BCR 33 = Sonoran and Mojave Deserts.
BCR 34 = Sierra Madre Occidental.
BCR 35 = Chihuahuan Desert.
BCR 36 = Tamaulipan Brushlands.
BCR 37 = Gulf Coastal Prairie.
SUM = sum of pixel counts for all NLCD categories.
Patch Density = expresses the number of patches on a per unit area basis that facilitates comparisons among landscapes of varying size.
Largest Patch Index = quantifies the percentage of total landscape area comprised by the largest patch.
Aggregation Index = the number of like adjacencies involving the corresponding class, divided by the maximum possible number of like adjacencies involving the corresponding class, which is achieved when the class is maximally clumped into a single, compact patch multiplied by 100.