ASSOCIATION OF SCISSOR-TAILED FLYCATCHERS (TYRANNUS FORFICATUS) WITH SPECIFIC LAND-COVER TYPES IN SOUTH-CENTRAL TEXAS

摘要

Scissor-tailed Flycatchers (Tyrannus forficatus) are insectivorous Neotropical migrants that breed in the south-central United States. We examined their fine-scale (circles 300 m in radius centered on observed flycatcher locations) associations with different land cover types in south-central Texas. Scissor-tailed Flycatchers use a sit-and-scan foraging strategy; therefore, we expected the species would be positively associated with open land cover types (vegetation with little or no canopy) such as grassland, pasture/hayfield and cropland, and negatively associated with forest and shrubland given that the latter could obstruct visual scanning. We conducted 44 surveys from 9 May 2011 to 15 December 2011 by slowly driving (30 km/h) rural roads throughout 15 counties in south-central Texas and 3 near the coast of the Gulf of Mexico. Using ArcGIS, we quantified the percent cover of four general land cover types (urban/developed land, forest/ shrub, grassland/pasture/hay, and cropland) within 300 m of each flycatcher location. Statistical analysis involved comparing the land cover of the flycatcher locations to a set of random points along the same routes. On average, flycatcher locations had significantly more grassland/pasture/hay than did random points (38.8 vs. 31.2%) and significantly less forest/ shrub (29.9 vs. 36.7%). Therefore, although flycatchers may associate with open land cover at a rate greater than its overall availability, they generally occupy locations that have a mix of open and closed land cover. Knowledge of flycatcher habitat use at a fine-scale could be useful to the successful conservation of this species.