Spatial pattern and temporal dynamics of northern bobwhite abundance and agricultural landuse, and potential casual factors

Abstract

There was a long-term decline in northern bobwhite (Colinus virginianus, NBW) abundance since the 1920s, based on the Christmas Bird Count (CBC) data, but with substantial spatial and temporal variations across its range. There were four recognizable periods in the spatial and temporal dynamics of NBW abundance between 1920 and 1990. Severe weather conditions and habitat loss due to land use change appeared to be the most important factors influencing the long-term trends and spatial patterns in NBW abundance. A spatial database of agricultural land use was developed based on the Census of Agriculture to evaluate the spatial patterns of land use variables over NBW range from 1920 to 1997. The results showed dramatic changes in land use over the period and the influence of socio-economic events, natural disasters and federal agricultural policies on the dynamics of land use pattern, and potential implications to NBW abundance were identified. Replacement of less intensive agriculture with intensive monoculture production and mechanization coincided with World War I, and the post-war collapse in agriculture and the economy, partly associated with the Dust Bowl, enhanced this trend. Monoculture production and clean farming practices were further intensified during World War II and the years following the war. These land use changes had overall negative effects on NBW habitat. Analysis of the changes in spatial pattern of NBW abundance in the Great Plains region during the severe drought of the 1950s showed a significant decline in NBW abundance during the drought and a contraction of the NBW range at its western edge. The post-drought recovery exhibited spatial patterns significantly different from the predrought ones. These findings suggested that severe drought caused short-term changes in regional distribution of NBW and range contraction, as well as long-lasting, largescale changes in spatial distribution of NBW abundance. This study provides scientific basis for landscape planning and management. Evaluating the spatial pattern and temporal dynamics of certain wildlife species at large scales over long-term periods, and identifying potential causal factors are key strategies for implementing innovative and sustainable approaches to planning and policy. Such strategies will have a significant impact on future landscape and wildlife species.