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We used multiple and logistic regression analysis to study the breeding-area requirements of 10 species of grassland and early-successional birds at 90 grasslandbarren sites in Maine The incidence of six of the species was clearly sensitive to the area of grasslamt Upland Sandpiper~ the species with the largest area requirement~ umre infrequent at sites of less than 50 ha and reached 50% incidence at those of about 200 ha Grasshopper Sparrows reached 50% incidence at about 100 ha, Vesper Sparrows at about20 I~ and Savannah Sparrows at about 10 hat Incidence for three edge specie~ Brown Thrashe~, Common Yellowthroa~ and Song Sparrow, was negatively correlated with open area~ and incidence for Field Sparrows was not strongly influenced by grassland size These results indicate that grasslands need to be approximately 200 ha in area if they are to be likely to support a diverse grassland bird fauna Ho~, large grasslands or grussland-barrens are rar~ random samples indicated that in Maine only 1% of hayfields and only 8% of grassland-barrens were more than 64 ha in area Conserva. tion efforts seeking to protect habitat for rare grassland birds "Current addres~ Center Los efectos de la superficie del habitat en la distribuci6n de los pfijaros de pastizales en Maine Resumen: En el presente estudio utiltzamos andlisis de re-gresi6n m~lttple y logisttca para estudlar los requerimtentos de las dreas de cria de 10 especies de aves de pastizales y aves comunes durante los estadtos sucecionales tempranos en 90 sitios de pastizales-dridos en Maif*~g EU& La tasa de ocurrencla de 6 especies fue claramente sensitiva al drea del pastizaL Los sandpipers de tierras alta~ la especie con los requerimientos de drea mds grande~ fue poco frecuente en sitios de menos de 50 ha y lleg6 al 50% de incidencia en sitios con unas 200 ha Los Grasshopper sparrows alcanzaron una tasa de ocurrencla de150% en sittos con 100 h~ los Vesper Sparrows 1o hicieron en sitios con 20 ha y los Savannah Sparrows en sittos con 10 h~ La tasa de ocurrencla para ires especies de los borde~ Brown Thrasher;, Common Yellowthroat y Song Sparrow, estuvo negattvamente correlacionada con el drea abierta y la tasa de ocurrencia~ pawa los Field Sparrow~ no estuvo fuertemente influer~iada por el tama~o del pasttzaL Estos resultados indican que los pastizales necesitan cubrir mds de 200 ha para poder man. tenet una fauna de pdjaros divets~ Sin embargo, las grandes extenciones de pastizales o pastizales-dridos son raras; muestras al azar indican queen Maine s61o un 1% de los campos de heno y un 8% de los pasttzales-dridos ocuparon mds de 64 la~ Los esfuerzos de conservaci6n que busquen

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A new method of measuring reproductive success was used to test Van Horne's (1983) contention that reliance on population density as a measure of habitat quality can produce misleading results. None of the three emberizine sparrows in this study showed a clear correlation between high territory density and high reproductive success. Grasshopper Sparrows (Ammodramus savannarum) were most successful in medium-density plots, and did poorly when territory density was low. Savannah Sparrows (Passerculus sandwichensis) were significantly more successful at low density, and were least successful at high density. Vesper Sparrows (Pooecetes gramineus) were the only species whose reproductive success was unaffected by territory density and, thus, for which density would have been a reasonable measure of habitat quality. These results lend support to Van Horne's thesis that the singular use of density may be a poor indicator of habitat quality and that additional factors should be considered.

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