Local and regional patterns of breeding dispersal and habitat selection in a declining grassland bird

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Dispersal is a critical behavior influencing meta-population dynamics, potential for local adaptation, and extinction risk under changing climates. Although less common than natal dispersal, some mobile animals engage in breeding dispersal between successive reproductive attempts. Such behavior confounds both accurate estimates of survival and our ability to devise effective management strategies. Breeding dispersal appears to be particularly prevalent in grassland ecosystems, yet the basic patterns of variation in dispersal behavior (within and among years) at local, regional, and continental scales, and the causes of that variation remain unknown. I report here on preliminary results from studies of individual variation in return rates and dispersal of >600 color banded Grasshopper Sparrows (Ammodramus savannarum) at the Konza Prairie LTER in NE Kansas, as well as a regional study of dispersal distances of the same species in the central Great Plains. Sparrows at Konza are remarkably transient with near complete turn-over of territory holders on local plots within the breeding season. Additionally, they exhibit habitat-specific seasonal shifts in territory density, and movements between breeding attempts of >4 km. Territory densities on plots exhibited management-specific temporal changes within years, and densities varied between years within the same management regime, perhaps due to the varying effect of fire under different precipitation conditions. However, there were few direct links between patterns of movement, density, and metrics of individual condition. Return rates were ~20% for adults and ~8% for first year birds, and many returning individuals settled on territories within 50 m of their last observed location the previous year. At regional scales, isotope data suggest that non-site-faithful birds often make large-scale dispersal movements. This result implies that factors influencing habitat quality regionally (such as inter-annual variation in rainfall) rather than local management practices or landscape-scale availability of grassland habitat may explain the high mobility of grassland birds.