The Botteri's Sparrow and exotic Arizona grasslands: an ecological trap or habitat regained?/Aimophia botterii y los pastizales exoticos de Arizona: ?una trampa ecologica o la conquista de nuevo habitat?

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Date: Nov. 2005
From: The Condor(Vol. 107, Issue 4)
Publisher: Cooper Ornithological Society
Document Type: Author abstract
Length: 548 words

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Abstract :

The Botteri's Sparrow (Aimophila botterii) is a bird of tall grasslands that temporarily disappeared from Arizona following heavy livestock grazing in the 1890s. Its return was noted first in sacaton (Sporobolus wrightii), an uncommon native floodplain tallgrass often 2 m in height, and subsequently in stands of exotic lovegrasses (Eragrostis spp.) spreading into adjacent uplands that otherwise supported shorter native grasslands. We examined whether the exotic grasslands provided suitable breeding habitat for Botteri's Sparrows, compared to native grasslands. We counted birds for three years on 18 plots, monitored 314 nests on 323 home ranges, banded 583 birds, and measured vegetation on plots and home ranges, and at nests and fledgling locations. Abundance and site fidelity were positively associated with grass height and cover, being greatest in sacaton, intermediate in exotics, and lowest in native upland grasslands. The three habitats did not differ in young fledged per capita. Vegetation cover on Botteri's Sparrow home ranges did not differ from the surrounding available habitat, but locations of flightless recently fledged young included taller and more dense vegetation than either nest sites of random locations, especially in sparsely vegetated native grasslands. These results suggest that fledglings required substantial cover to avoid predation while they completed development. Far from being an ecological trap, the exotic lovegrasses apparently are providing essential cover for the Botteri's Sparrow in Arizona, perhaps allowing it to regain an abundance similar to what existed regionally prior to overgrazing of the late 19th Century. Key words: Botteri's Sparrow, ecological trap, exotic grasses, habitat quality, habitat structure, livestock grazing, reproductive success. Aimophia botterii es un ave que desaparecio temporalmente de Arizona debido al pastoreo intensivo en la decada de 1890. El ave retorno a Arizona primero a pastizales de hierbas nativas de Sporobolus wrightii, una especie poco comun de mas de 2 m de altura de las planicies inundables, y posteriormente a pastizales exoticos de Eragrostis spp que se expandian a tierras altas adyacentes que de otro modo presentaban pastizales nativos cortos. En este estudio examinamos la calidad del habitat de los pastizales de hierbas nativas y exoticas para la reproduccion y alimentacion de A. botterii. Censamos la abundancia de A. botterii en 18 parcelas de estudio durante tres anos, monitoreamos el exito de 314 nidos en 323 territorios, anillamos 583 individuos, y estudiamos la vegetacion de los territorios y de las localidades de anidacion. La abundancia y la fidelidad de territorio en A. botterii estuvieron positivamente correlacionadas a la altura del pasto y a la cobertura del terreno, siendo mas alta la correlacion en S. wrightii, intermedia en Eragrostis spp. y baja en pastizales nativos. Sin embargo, los tres tipos de habitat no difirieron en la produccion per capita de polluelos. No encontramos diferencias entre la vegetacion en los lugares de anidacion y las areas circundantes. Los polluelos volantones prefirieron lugares de pasto mas alto y denso que el de las areas de anidacion, especialmente en los ambientes de pasto nativo. Estos resultados sugieren que los polluelos volantones requieren buena cobertura vegetal para protegerse de los depredadores mientras completan su desarrollo. Lejos de ser una "trampa ecologica", las hierbas exoticas actualmente proveen un habitat esencial para A. botterii en Arizona y quizas han ayudado a que la especie vuelva a alcanzar los niveles de abundancia anteriores al siglo XIX.

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Gale Document Number: GALE|A139345052