Fine-scale Habitat Associations of Scissor-tailed Flycatchers (Tyrannus forficatus) in south-central Texas
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During the last century, North America’s grasslands have been severely reduced in area due to land-use change and development. Subsequently, grassland birds have experienced declines, with only 18% of grassland breeding birds increasing or stable in abundance. Birds may respond to habitat structure at different spatial scales and many studies of habitat selection in grassland birds have demonstrated that birds cue into specific structural features of vegetation. Scissor-tailed Flycatchers are insectivorous, neo-tropical migrants that breed in the south-central US. I examined their fine-scale (300 m) habitat associations in south central Texas. I predicted that Scissor-tailed Flycatchers would be positively associated with open habitats such as grasslands, pasture and hay fields since these habitats facilitate their scanning foraging strategy, and negatively associated with forest. I conducted 44 surveys from 9 May 2011 to 15 Dec 2011 by slowly driving rural roads throughout fifteen counties in central Texas and three along the coast. Four routes were repeated five times each to allow testing of seasonal differences in habitat use. I recorded the GPS locations of all flycatchers encountered on the routes. Using aerial imagery in Google Earth, I measured the distances to the nearest tree and human-built structure for each flycatcher location. Using ArcGIS, I quantified the percent cover of five habitat types within 300 and 170 m of each flycatcher location. Statistical analysis involved comparing the habitat variables of the flycatcher locations to a set of random points along the same routes. There was a significant difference between the flycatcher locations and the random points in the amount of grassland/pasture/hay and forest and urban land. Flycatchers were positively associated with grassland/pasture/hay. Knowledge of the fine-scale habitat associations of Scissor-tailed Flycatchers and other grassland birds could be useful to the successful conservation of these species.