Cassin's Sparrow is highly responsive to vegetative structure of arid shrub grasslands, and therefore, is potentially affected by grazing, shrub clearing, and other human activities that change habitat structure (135, 12). The species did not occupy moderately to heavily grazed rangeland in southeastern Arizona, but did occupy adjacent ungrazed grassland (14, 67). Chaining or cutting of shrub (to improve rangeland for livestock) decreases habitat suitability by eliminating song perches, since Cassin's Sparrow does not occupy pure grasslands. On the other hand, Cassin's Sparrow was the fourth most common breeding species at an Arizona grassland site on which mesquite had increased substantially in 1900s (15), but see Maurer (136) for evidence that mesquite control can benefit Cassin's Sparrow. Increase in mesquite cover is a possible consequence of grazing and/or fire suppression. Conservation Reserve Program (CRP) fields are suitable if planted in native grasses (125) but seed-mix composition can affect habitat occupancy (109). Cassin's Sparrow breeds more abundantly in native Arizona grasslands compared to grasslands dominated by exotic lovegrasses (Eragrostis spp.) (92).
Long et al. (137) suggested that more research is needed on management impacts on birds of short-grass prairie, as opposed to better researched tall-grass prairie. They found few significant responses of Cassin’s Sparrow and sympatric breeding species in areas treated with prescribed burning to control Honey Mesquite (Prosopis glandulosa) in grasslands near Amarillo, Texas. Sparrow abundance increased in one fire treatment in one year (2-year study); lack of strong response probably due to little mesquite reduction due to burning after 7 years of treatment in this study area (137).
Similarly, Holcomb et al. (19) found few treatment effects in study of burning and grazing in Oklahoma shrub grasslands dominated by sand sagebrush. Treatments included patch-burning (small-size, but intense prescribed burning) followed by short-term grazing compared to traditional seasonal grazing. Reproductive success and breeding abundance of Cassin’s Sparrow were not significantly different among treatments. Holcomb et al. (19) concluded that patch burning and grazing (“pyric herbivory”) may be good management strategy as it results in higher avian species diversity without negative effect on grassland specialists such as Cassin’s Sparrow.
Fire and herbicides are increasingly used as management tools in southwestern grassland restoration to limit invasions of shrubs such as mesquite (Prosopis sp.). Coffman et al. (18) found no effect on abundance of Cassin’s Sparrow (or other grassland indicators) beyond first year of herbicide treatment for shrub control in southwestern New Mexico. In Harvard Oak (Quercus havardii) communities, singing male densities doubled in restoration patches treated with herbicide (Tebuthiuron) to reduce woody stem density and increase grass cover; effect of grazing not significant (17). Detection rates of wintering Cassin’s Sparrow did not differ consistently between burned and unburned Arizona grassland patches, comparing sites burned in spring and/or summer; suggesting “effect of spring fire is ambiguous” in terms of wintering habitat quality (16).
Thompson et al. (109) found that Texas breeding Cassin’s Sparrow populations were more common in CRP fields seeded with mixes of native grass species that did not include buffalograss (Bouteloua dactyloides). Thompson et al. (109) suggested that seed-mix type can be important factor in assessing quality of CRP restoration efforts.
Female sits tight on nest as human observers approach; may perform distraction display as she leaves nest. Male gives Psit Call from low, hidden perch when observer approached nest with young (29). More intense response from both parents occurs as young are handled, including chattering, close approach by parents to observer, extension of wings. No information on effect of human disturbance on nest success.
Near major cities and towns, habitat is lost to urban development and sprawl. Reliable sites near Tucson and Sonoita, Arizona, have been converted to housing developments, including the Wilmot Cienega, site of RKB's studies of wintering and migratory status. Not recorded in Tucson residential neighborhoods by Mills et al. (138), although several of the neighborhoods studied were in former grassland habitats and retained some native vegetation (JBD).