Plant invasions alter settlement patterns of breeding grassland birds

Abstract

Citation: Andersen, E. M., and R. J. Steidl. 2020. Plant invasions alter settlement patterns of breeding grassland birds.Abstract. Animals have evolved strategies to identify areas that provide the resources and environmental conditions they need to survive and reproduce. To explore how invasions by nonnative plants might disrupt this fundamental process, we evaluated settlement patterns of migratory birds that breed in grasslands being invaded by two structurally different congeneric grasses. We established 40, 2.25-ha plots across an area where the composition of each nonnative grass ranged from 0% to nearly 100% of total grass cover, which provided individuals with the full range of alternatives in species composition. We then used the temporal sequence by which birds established territories to infer their habitat preferences. We evaluated responses of the most common species that settled the area, two confamilial sparrows that differed markedly in habitat breadth. The species with narrower habitat breadth, the grasshopper sparrow (Ammodramus savannarum ammolegus), first established territories in areas dominated by native grasses, where grass height and cover were substantially lower than in areas dominated by the nonnative grasses. As the settlement period progressed, they increasingly established territories in areas dominated by the smaller nonnative grass (Eragrostis lehmanniana), but never established territories in areas dominated by the larger grass (E. curvula). In contrast, the species with broader habitat breadth, the Botteri's sparrow (Peucaea botterii arizonae), established territories without regard to grass composition, likely because both nonnative grasses were within the structural range of native grasses used by this grassland generalist. Our results demonstrate that in areas invaded by nonnative plants, changes in habitat use by animals can reflect the interaction between their habitat breadth and the amount of structural contrast between invading plants and the native plant species that are displaced. This interaction provides a mechanism to explain the variation in responses among species to invasions by nonnative plants, which has consequences for broadscale changes in the geographic distribution of many species.

Springtime bird use of agricultural landscapes examined by using autonomous recording units

“…Grassy areas with established non-native grasses are structurally different from prairies, with substantially higher grass height and cover. They have been associated with temporal and spatial shifts in breeding patterns of grassland birds (Andersen and Steidl 2020).…”

Woody plant encroachment drives population declines in 20% of common open ecosystem bird species

“…For example, at a local scale, increased woody cover can cause reorganisation of mammalian herbivore communities, benefitting smaller bodied browsing herbivores over larger bodied grazers (Smit & Prins, 2015). Similarly, reorganisation of bird communities can occur with encroachment, often favouring leaf gleaning, smaller bodied invertivorous passerines over larger bodied, non‐passerine ground dwelling birds (Andersen & Steidl, 2019, 2020; Péron & Altwegg, 2015; Sirami & Monadjem, 2012). It is likely that open system specialists will be disproportionately impacted as they are area sensitive and require large open area habitats to reproduce (Andersen & Steidl, 2020; Reino et al., 2009).…”

The effects of management practices on grassland birds—Grasshopper Sparrow (<i>Ammodramus savannarum</i>)

“…In southeastern Arizona desert grasslands, Andersen and Steidl (2020) examined the response of Grasshopper Sparrows along a gradient of dominance ranging from 0 to 100 percent of total grass cover for two tame species of lovegrass, Lehmann lovegrass (Eragrostis lehmanniana) and weeping lovegrass (Eragrostis curvula), to examine whether structural differences between nonnative plants and the native plants that they displaced can alter the quantity of habitat available to animals, especially species with narrow habitat breadths. During the first 2 weeks of the settlement period, Grasshopper Sparrows established breeding territories on plots dominated by native grasses, which tended to be shorter and less dense but more structurally heterogeneous and floristically diverse than areas dominated by either tame species.…”

“…As the settlement period progressed and native-dominated areas became occupied by conspecifics, Grasshopper Sparrows increasingly established territories in areas dominated by Lehmann lovegrass, which is more structurally similar to native grasses than weeping lovegrass, but did not establish territories on plots where weeping lovegrass exceeded 21 percent of grass cover. Andersen and Steidl (2020) suggested that Grasshopper Sparrows preferred areas dominated by native plants in the absence of conspecific competition, and that the species may have perceived areas dominated by Lehmann lovegrass as suitable breeding habitat and areas dominated by weeping lovegrass as unsuitable breeding habitat. In coastal sand and southern Texas plains communities, Bielfelt (2013) examined the response of Grasshopper Sparrows across a gradient of dominance of tanglehead (Heteropogon contortus), a native grass species with growth characteristics of an invasive plant that is becomingly increasingly prevalent in southern Texas, especially in areas with clay loam soils.…”