Effects of Habitat Area on the Distribution of Grassland Birds in Maine

Abstract

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

Population trends of grassland birds in North America are linked to the prevalence of an agricultural epizootic in Europe

“…For example, organochlorine pesticides applied to hayfields may accumulate to potentially hazardous levels in grassland birds (8). Hayfields frequently are small and highly fragmented, characteristics that are associated with reduced nest success (9,10). Hay harvest also can change vegetation structure, reducing prey abundance (11).…”

Effects of management practices on grassland birds: Field Sparrow

“…Field Sparrows prefer woody edges and dry to slightly mesic, moderately tall grasslands with moderately abundant litter and a shrub component (Best 1977(Best , 1978Sousa 1983;Sample 1989;Herkert 1991a). Suitable habitat includes oldfields, sage (Artemisia) flats, weedy pastures, untilled and idle cropland, Conservation Reserve Program fields, grassed waterways, hedgerows, shelterbelts, orchards, woodland edges, brushy woodlands, wooded draws, pine (Pinus) plantations, attenuated gallery and gallery forest, and reclaimed strip mines (Gabrielson 1914;Ely 1957;Graber and Graber 1963;Walkinshaw 1968Walkinshaw , 1978Stewart 1975;Best 1977Best , 1978Evans 1978;Johnsgard 1980;Stauffer and Best 1980;Whitmore 1980;Best et al 1981Best et al , 1997Faanes 1981Faanes , 1983Buech 1982;Hopkins 1983;Sousa 1983;Dinsmore et al 1984;Kahl et al 1985;Basore et al 1986;Sample 1989;Bryan and Best 1991;Herkert 1991a;Cable et al 1992;Zimmerman 1993;Carey et al 1994;Vickery et al 1994;Faanes and Lingle 1995).…”

Effects of management practices of grassland birds: Savannah Sparrow

“…In Illinois, Herkert (1991a,b,c) found no Savannah Sparrows on grassland tracts <10 ha and noted that they were significantly more likely to occur on large than small grasslands. Savannah Sparrow incidence increased with area and reached 50% at about 10 ha in Maine (Vickery et al 1994) and 40 ha in Illinois (Herkert 1994a).…”

“…), or between treated fields and control fields (Knapton and Mineau 1995). In Maine, territory density of Savannah Sparrows decreased for 2-6 yr following the application of the herbicide hexazinone at a rate of 4 kg/ha on lowbush blueberries (Vaccinium angustifolium) (Vickery 1993).…”