How Tropicbirds Behave at Sea

28 fledged per nest in the native habitat, but only 1.0 per nest in the wheatgrass, Lloyd and Martin reported in 2005 (Condor 107:363–374). These significantly different success rates resulted primarily from greater nest predation in the wheatgrass. The odds of a nest surviving a given day were 17 percent higher in the native-prairie patches than in the wheatgrass plots. Nestlings in the native habitat had two advantages: They grew faster, and they weighed an average of 9 percent more at fledging than those in the exotic habitat. Slower growth would extend the nestlings’ period of vulnerability to nest predators, and smaller size has been linked in other songbird studies to a lower probability of survival, the authors said. Unfortunately, the longspurs showed no preference for nesting in native mixed-grass habitat. They were almost as likely to choose the lessproductive wheatgrass. Densities of nesting pairs in the study plots did not differ statistically at 1.8 pairs per hectare in the native habitat and 1.2 pairs in the exotic grass—a self-defeating lack of discrimination. Lloyd and Martin pointed out that crested wheatgrass continues to be planted on lands in the Conservation Reserve Program. This federally subsidized program is meant primarily to prevent soil erosion by helping farmers and ranchers to cover marginal lands with perennial vegetation, but it is also viewed as an opportunity to improve habitat for grassland wildlife. The type of vegetation is clearly crucial. A report by the U. S. Geological Survey’s Northern Prairie Wildlife Research Center in 2002 pointed in extensive detail to the importance of native grasses in Chestnut-collared Longspur habitat. The North American Landbird Conservation Plan published by Partners in Flight in 2004 recommended an increase in the use of native plants on conservation-reserve lands. The research by Lloyd and Martin adds further support. In effect, their results say it loud.