A multi-scale occupancy model for the grasshopper sparrow in the Mid-Atlantic

Abstract

Identifying features of breeding habitat that influence occupancy and modeling the distribution of grassland birds is needed to direct conservation efforts to reduce population declines associated with habitat loss and fragmentation. Many recent studies on grassland bird habitat use incorporate both local and landscape attributes. However, few studies have determined the appropriate spatial scales at which to measure these relationships. We conducted roadside point counts within Delaware, USA, to determine the presence of grasshopper sparrows (Ammodramus savannarum). We quantified both land cover composition and configuration at local and landscape scales at our survey sites using data from the National Oceanic and Atmospheric Administration Coastal Change Analysis Program. We determined the spatial scales at which grasshopper sparrow presence was most strongly related to landscape metrics and modeled grasshopper sparrow habitat occupancy at multiple scales, while accounting for variation in detection. At the site scale, occupancy was negatively related to forest and shrub composition. At the landscape scale, grasshopper sparrow occupancy was positively related to the amount of grasslands and pastures, and negatively related to mean inter‐patch distance of grasslands and amount of low‐intensity development. Our model had good predictive accuracy (area under the receiver operating characteristics curve = 0.717). We present our predictive model applied to the Delmarva Peninsula, USA. © 2013 The Wildlife Society.

Subdivision design and stewardship affect bird and mammal use of conservation developments

“…This result is consistent with past studies that have found impacts of landscape‐scale land cover on passerines, despite their relatively small home ranges (Knick and Rotenberry , Irvin et al. , Lee and Carroll ). A majority (79%) of the CDs that we examined had a total area of protected space that was less than 200 ha, and eight (57%) were smaller than 100 ha.…”

“…It appears that CDs may function as part of a larger network of undeveloped or protected space, which renders the total area of an individual CD open space less important to many birds. This result is consistent with past studies that have found impacts of landscape-scale land cover on passerines, despite their relatively small home ranges (Knick and Rotenberry 2002, Irvin et al 2013, Lee and Carroll 2014. A majority (79%) of the CDs that we examined had a total area of protected space that was less than 200 ha, and eight (57%) were smaller than 100 ha.…”

“…), and at a buffer distance scaled to the average home range size for each mammal detected in the study (Irvin et al. ).…”

“…We also measured the proportion of natural land cover, which included all vegetated land cover types, but excluded agriculture, recently disturbed or modified land, and land that is developed or in other human uses (USGS National Gap Analysis Program 2011). Housing density and all land cover types were measured at local scales (within 200 m and 500 m of each sampling point), at broad scales (within 1 km, 2 km, and 3 km of each sampling point) (Wells et al 2011), and at a buffer distance scaled to the average home range size for each mammal detected in the study (Irvin et al 2013).…”

Grasslands bird occupancy of native warm‐season grass

“…Occupancy models can be used to determine key variables affecting species distributions, especially in the context of grassland bird habitats (Olson et al , Nicholson and Van Manen ). Irvin et al () used multi‐scale occupancy models to show that at broad scales (5–8 km), grasshopper sparrow ( Ammodramus savannarum ) occupancy on the Delmarva Peninsula was positively associated with the amount of grassland habitat, and negatively associated with amount of development and forest. Alternatively, Hill and Diefenbach () reported that landscape‐level variables did not influence grasshopper sparrow or Henslow's sparrow ( Ammodramus henslowii ) site occupancy on reclaimed minelands; rather field shape and size were the most influential variables explaining occupancy patterns.…”