Nesting Ecology of the Rusty Blackbird in Alaska and Canada

Abstract

Resumen. examinamos la ecología de nidificación de Euphagus carolinus a través del monitoreo de 162 nidos para obtener datos de supervivencia de nidos en alaska y de 252 registros adicionales de alaska y canadá para identificar habitats importantes para la nidificación y evaluar si las bajas tasas de éxito de nidos contribuyeron a las disminuciones poblacionales en alaska. en la costa de alaska y a lo largo de canadá, los nidos se encontraron principalmente en coníferas (85% de 212 nidos). todos los nidos en coníferas de alaska y el 80% de los de canadá estuvieron ubicados en ejemplares de Picea spp., principalmente P. mariana. en alaska se identificó un uso selectivo de ejemplares pequeños de Picea (<8 cm dap), resultando en un alto éxito reproductivo-la supervivencia de los nidos incrementó con la densidad de P. mariana, y el éxito de nidos en ejemplares de Picea (79%) fue mayor que el de los nidos ubicados en vegetación decidua (52%). la supervivencia de nidos en ejemplares más altos de Picea disminuyó, posiblemente debido a la depredación por parte de Tamiasciurus hudsonicus. los individuos de E. carolinus nidificaron cerca del agua en el interior (x _ = 8 m) y en el sur centro de alaska (x _ = 30 m), y los ejemplares pequeños de Picea parecieron ser importantes dentro de la mayor parte del área de distribución de la especie. Sin embargo, en el interior de alaska, la mayoría de los nidos se ubicaron en ejemplares de Salix (78%), los que dominaban la vegetación cercana al agua. el éxito de nidos en alaska promedió el 56%, similar a las tasas del mismo periodo en nueva inglaterra pero mayor que las de otras especies de Euphagus de américa del norte. Son necesarios estudios para verificar si la supervivencia de nidos es alta también en canadá y para investigar dónde y cómo el déficit en la supervivencia de adultos o juveniles puede estar limitando el crecimiento poblacional.neSting ecology of the RuSty BlackBiRd in alaSka and canada ecología de nidificación de Euphagus carolinus en alaska y canadá Abstract. we examined the nesting ecology of the Rusty Blackbird (Euphagus carolinus) from 162 nests monitored for nest survival in alaska and 252 incidental records from alaska and canada to identify important habitats for nesting and to test whether low rates of nest success are contributing to populations declines in alaska. in coastal alaska and throughout canada, nests were primarily in conifers (85% of 212 nests). all conifer nests in alaska and 80% of those in canada were placed in spruce (Picea spp.), primarily black spruce (P. mariana). in alaska use of small spruces (<8 cm dbh) was selective and resulted in high reproductive success-nest survival increased with black spruce density, and success of nests in spruce (79%) was higher than that of nests in deciduous vegetation (52%). Survival of nests in taller spruce declined, possibly from predation by red squirrels (Tamiasciurus hudsonicus). Rusty Blackbirds nested near water in interior (x _ = 8 m) and south-central alaska (x _ = 30 m), and small spruces near ...

Estimating the Abundance of Nesting Rusty Blackbirds in Relation to Wetland Habitats in Alaska

“…We conducted our rapid surveys between 06:00 and 13:00 and from 11 to 23 May, the period from pair formation to early incubation (Matsuoka et al 2010) and the time when we expected detection rates to be relatively high because most females would not yet be incubating their eggs and most males would still be actively singing and closely guarding their mates. We did not constrain our surveys to the early morning because previous work indicated that detectability of breeding Rusty Blackbirds does not vary over the morning (P. Blancher, unpubl.…”

“…Surface water is largely limited to ponds, lakes, and estuaries and nearby areas with shallow water and emergent wetland vegetation. The plant species in Anchorage wetlands are similar to those on the Tanana Flats, but black spruce is more common and willows ( 1 m in height) are less common (Matsuoka et al 2010). At Anchorage, all wetlands were accessible by road, foot, or canoe.…”

Rusty Blackbird: Mysteries of a Species in Decline

“…Matsuoka et al (2010a) and Powell et al (2010a) respectively surveyed and radio-tracked breeding Rusty Blackbirds and found that the generally low breeding densities observed over much of the species' range are linked to specialized use of shallow-water habitats for foraging and large home ranges, which typically include multiple wetlands used for foraging and nesting. Matsuoka et al (2010b) and Powell et al (2010b) analyzed data from >450 nests across the breeding range and showed that the species' widespread use of small stunted conifers, primarily spruce (Picea spp. ), for nest sites is selective and leads to relatively high rates of nest survival when nests are placed in undisturbed wetlands in Alaska and New England.…”

“…Thus, buffers from logging around wetlands ought to be explored as a conservation measure to protect nesting Rusty Blackbirds from these negative consequences (Powell et al 2010b). 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 cross-seasonal approach may be particularly needed to understand when and where deficits in juveniles' or adults' survivorship limit population growth because nesting success is not clearly limited (Matsuoka et al 2010b).…”