Increasing and Declining Populations of Northern Bobwhites Inhabit Different Types of Landscapes

Northern bobwhites (Colinus virginianus) have been declining in abundance throughout their range for several decades, and perhaps a century. Although wildlife biologists are well aware of this trend, most attempts to understand the declines have examined only a few local populations in a limited geographic area or have examined declines at a very large scale without reference to specific populations. Few studies use a standard protocol for examining trends in local populations throughout the entire natural range of bobwhites. I used the National Resources Inventory, a geographically extensive and intensive database on land cover and use, to characterize the composition and heterogeneity of landscapes inhabited by bobwhite populations that have been increasing (43 populations), decreasing (468), or become locally extinct (28). I tested bobwhite populations for overall positive or negative change, over the past 10 years or more, using data from the North American Breeding Bird Survey and a randomization test that controls for observer effects. Landscapes occupied by increasing and decreasing populations were, on average, different from one another in composition but not heterogeneity. As predicted, landscapes of decreasing populations tended to have a greater percentage of nonuseable land (e.g., urban and forestland) and a lesser percentage of useable land (e.g., cropland, pastures, and rangeland) as compared to landscapes where bobwhites actually increased. Moreover, landscapes where bobwhites had recently become extinct were different from those where bobwhites were only declining. In particular, a very large percentage of urban land characterized the landscapes of extinct populations. To some extent, landscapes of large (above average) and small (below average) populations also differed as predicted. The results do not point to a single universal explanation for bobwhite declines, but they do clearly show that declining populations inhabit local landscapes that, on average, are very different from those occupied by increasing populations. This knowledge may assist quail biologists and land managers to recognize the general type of landscape where the restoration of bobwhites may be most successful and where extant populations may be most threatened. (JOURNAL OF WILDLIFE MANAGEMENT 70(4):922–930; 2006)