Demographic and dispersal data from anthropogenic grasslands: what should we measure?

Studies of population dynamics of grassland birds have often followed the source–sink paradigm of Pulliam (1988). We present examples of demographic, dispersal, and modeling studies done with bird species found in anthropogenic grasslands of the midwestern USA. Although we believe that we have gained valuable insights into the factors that affect bird populations found in restored grasslands, hayfields and pastures, some of the demographic and dispersal processes assumed in Pulliam (1988) are difficult to measure with grassland birds. More importantly, the population dynamics of many migratory birds do not follow the structure of individual-based models used in the study of source–sink dynamics as pioneered by Pulliam (1988). We suggest measures of population stability such as territory occupancy, age distribution of successful dispersers, production of offspring, and dispersal may be useful as an alternative for assessing the health of grassland breeding bird populations.