Habitat Occupancy by Rusty Blackbirds Wintering in the Lower Mississippi Alluvial Valley

Abstract

Resumen. las poblaciones de Euphagus carolinus han disminuido en un 90% desde la década del sesenta, posiblemente por la conversión de humedales arbolados a áreas agrícolas en el sureste de los estados unidos. debido a que el uso de hábitat por parte de E. carolinus durante la época no reproductiva no ha sido cuantificado, estimamos sus tasas de ocupación invernal en el valle aluvial bajo del Mississippi en relación con el tipo de hábitat (cuatro tipos de bosques de bajura y campos agrícolas adyacentes), la densidad de árboles, la cobertura del dosel y la cobertura de agua. en enero y febrero, censamos 89 sitios en ocho ocasiones en 2006, y 117 y 109 sitios en 10 ocasiones en 2007 y 2008, respectivamente. la ocupación de aves individuales, estimada a partir de su presencia o ausencia en un sitio, fue generalmente alta y mayor en 2006 (0.71) que en 2007 (0.43) y 2008 (0.37). la ocupación de las bandadas, estimada a partir de la presencia de 20 o más individuos, fue máxima en 2006 (0.46), mínima en 2007 (0.17) e intermedia en 2008 (0.30), posiblemente debido a las fluctuaciones en los niveles de agua entre años. la especie no se especializó tanto en el uso de hábitat como se esperaba; las características del hábitat no predijeron consistentemente la ocupación de individuos o bandadas. la ocupación de individuos aumentó con la cobertura del dosel en 2007 y la ocupación de bandadas disminuyó con la densidad de árboles en 2006. en 2008, la ocupación de individuos aumentó con la densidad de árboles y fue mayor en bosques húmedos de bajura (0.51) que en otros ambientes (0.31-0.35). Se necesita más investigación para determinar si la ausencia de especificidad de hábitat está ampliamente difundida y si posiblemente es el resultado de requerimientos alimenticios diversos durante la época no reproductiva. haBitat occupancy By RuSty BlackBiRdS winteRing in the loweR MiSSiSSippi alluVial Valley ocupación del hábitat de invierno por Euphagus carolinus en el Valle aluvial Bajo del MississippiAbstract. the Rusty Blackbird (Euphagus carolinus) has declined by 90% since the 1960s, possibly from conversions of forested wetlands in the southeastern u.S. to agriculture. Because its habitat use during the nonbreeding season had not been quantified, we estimated occupancy rates of Rusty Blackbirds wintering in the lower Mississippi alluvial Valley in relation to habitat type (four types of bottomland forest and adjacent agricultural fields), tree density, canopy cover, and water cover. in January and february, we surveyed 89 sites eight times during 2006, 117 and 109 sites 10 times during 2007 and 2008, respectively. occupancy of individual birds, estimated from their presence or absence at a site, was generally high and greater in 2006 (0.71) than during either 2007 (0.43) or 2008 (0.37). occupancy of flocks, estimated from presence or absence of ≥20 individuals, was highest in 2006 (0.46), lowest in 2007 (0.17), and intermediate in 2008 (0.30), possibly because of water levels fluctuating from year to year. Rusty Blackbirds were not ...

Rusty Blackbird: Mysteries of a Species in Decline

“…Average rates of nest success in Alaska (56%; Matsuoka et al 2010b) and New England (62%; Powell 2008) are not at chronically low levels that could be linked to long-term declines, so factors reducing survival of adults or juveniles are likely limiting population growth (Matsuoka et al 2010b). Luscier et al (2010) conducted the first formal surveys targeting wintering Rusty Blackbirds and modeled occupancy to show that birds wintering in the lower Mississippi Alluvial Valley are commonly found in a variety of forested wetlands but often are observed in adjacent agricultural fields, where they sometimes feed in loose association with other blackbirds. The species appears to depend on forest wetlands with open water but may use nearby disturbed sites, possibly to feed on waste grains and weed seeds to supplement its principal winter diet of aquatic and terrestrial invertebrates (Beal 1900) and acorn masts and pine (Pinus sp.)…”

“…Researchers are using counts (Luscier et al 2010), a variety of measures of condition (C. Mettke-Hofmann and P. Newell, unpubl. data), and age and sex ratios to compare sites.…”

Climate change and the decline of a once common bird

“…Within the boreal forest, the Rusty Blackbird breeds in bogs, beaver (Castor canadensis) ponds, streamsides, and other wet forest types where it forages primarily for aquatic insects (Avery 1995;Matsuoka et al 2010). The Rusty Blackbird also prefers wet wooded areas within its winter range, although it will also forage in agricultural areas (Avery 1995;Luscier et al 2010). During winter, the Rusty Blackbird will eat insects as well as pine and acorn mast and some fruit (Avery 1995) Although the Rusty Blackbird was once abundant, populations have fallen sharply over the past century (Greenberg and Droege 1999).…”

Rusty blackbird patch use during winter in suburban landscapes

“…These patch aggregations include fragments of shallowly flooded forested wetlands and creeks, residential areas with ornamental oak and pecan ( Carya illinoinensis ) trees, and abandoned or partially harvested pecan groves (Luscier et al , DeLeon , Borchert , Mettke‐Hofmann et al , Newell Wohner et al ). The species has adjusted to suburban landscapes (Meanley , Luscier et al , DeLeon , Newell Wohner et al ). For example, some of the largest and most persistent flocks in the eastern population occur sporadically in suburban areas on the Piedmont Plateau (Hamel and Ozdenerol ).…”

“…wetlands to acquire leaf litter-inhabiting invertebrates and they supplement their diet with mast from small-seeded oak species, such as water (Q. nigra) and willow oak (Q. phellos; Greenberg et al 2011, Avery 2013. Large rusty blackbird flocks (i.e., >100) use 2 contrasting landscape types for winter foraging: extensively forested, shallowly flooded bottomland hardwood wetlands typical of historical habitat for the species (Avery 2013, Mettke-Hofmann et al 2015, and a more recently available landscape type consisting of anthropogenic patches (Luscier et al 2010, Greenberg et al 2011, DeLeon 2012, Borchert 2015, Mettke-Hofmann et al 2015.…”