Johnson et at. • MIGRATION PATH OF RUSTY BLACKBIRDS 
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stopover areas was 60% cropland, 36% grassland, 
2% water. 1 % wetland, and 1 % other. 
The birds arrived in wintering areas between 20 
and 30 November; 72-84 days following depar¬ 
ture from breeding areas. Wintering areas differed 
among the three birds and included South Dakota, 
Nebraska. Kansas. Oklahoma. Arkansas, and 
northern Louisiana (Fig. 1). Distance from breed¬ 
ing sites to wintering areas ranged from 3,854 to 
5.027 km (x = 4.430 km). Core winter ranges for 
the male and one female wintering in the Central 
Mixed Grass Prairie and Prairie Potholes regions 
were 99% cropland and grassland habitats, 
whereas the winter range of the female in the 
Western Gulf Coastal Plain contained 51% 
coniferous forest, 17% deciduous woodland, 
18% wetland. 4% other, and only 10% cropland 
and grassland. 
Spring departure from core wintering areas 
occurred during 1-13 April. The male and lemale 
that wintered in the Central Mixed Grass Prairie 
and Prairie Potholes stopped in northwestern 
Alberta during 20-26 April before flying the 
remaining 1,820-1.840 km to Anchorage in 4— 
5 days (.v = 366 km/day; Figs. 1A and 1C). The 
female that wintered in the Western Gulf Coast 
Plain migrated through this same area, hut did not 
appear to stop (Fig. IB). Instead, she stopped in 
southeastern Saskatchewan and northwestern Brit¬ 
ish Columbia between 13-19 April and 1-4 May. 
respectively. All three birds followed spring routes 
that approximately matched their migration routes 
the previous autumn. The two birds that wintered in 
the Central Mixed Grass Prairie and Prairie 
Potholes arrived at their Anchorage breeding areas 
on 30 April and the bird that wintered in the 
Western Gulf Coast Plain arrived on 6 May. 
Duration of spring migration was 16-30 days. 
DISCUSSION 
We provide the first description of the annual 
movements of the Rusty Blackbird, a temperate 
migrant we documented to move in stages over a 
prolonged autumn (72-84 days) and briefer spring 
migration (16-30 days). The Prairie Potholes 
region, from southern Saskatchewan to Iowa, 
was an important stopover region during both 
autumn and spring migrations; all three birds 
stopped in North or South Dakota or both. Our 
data indicate at least these three Alaska breeding 
birds overwintered along the western portion of 
the species' principal wintering range. I wo birds 
overwintered in areas shown by Christmas Bird 
Count data (1946-2011) to have relatively high 
occurrence of Rusty Blackbirds—(I) the Arkansas 
River Valley along the Kansas-Oklahoma border, 
and (2) the Western Gulf Coast Plain from the 
Ouachita Mountains south to northern Louisiana 
(Hamel and Ozdenerol 2009). A third bird 
overwintered in an area spanning South Dakota 
and Nebraska, a region with a lower rate of 
occurrence during winter (Hamel and Ozdenerol 
2009). The species has recently been found, based 
on feather isotopes and band recoveries, to have 
separate Mississippi and Atlantic flyways (Hamel 
et al. 2009, Hobson et al. 2010). Data for our 
Alaska breeding population indicate the additional 
possibility of a Central Fly way route, which is also 
supported by limited numbers of band recoveries 
(Hamel et al. 2009: fig. 1). Alternatively, the 
western distribution of wintering birds in our study 
may have reflected an interannual shift in the core 
winter range that is thought to occur in response to 
variation in winter weather across years (Hamel 
and Ozdenerol 2009. Luscier et al. 2010). The 
winter of 2009-2010 was particularly cold in the 
eastern U.S. (NOAA 2011) and may have pushed 
birds farther west than during a typical year. 
The duration and timing of autumn stopover 
estimated from geolocators (19 Oct to 29 Nov) 
was similar to observations of migrating Rusty 
Blackbirds using wetlands farther east at Buckeye 
Lake, Ohio (15 Oct to 15 Nov; Trainman 1940). 
Rusty Blackbirds complete prebasic moll by late- 
September (Mettke-Hofmann et al. 2010). Thus, 
late autumn may be a distinct phase in the annual 
cycle during which Rusty Blackbirds rest from 
migration to forage in wetlands and agricultural 
areas over a I-month period before traveling to 
overwintering areas farther south. Populations 
may be susceptible to habitat losses and alter¬ 
ations in key stopover regions as hypothesized for 
wintering areas (Greenberg and Droege 1999, 
Greenberg et al. 2011). The species uses similar 
routes for spring and autumn migration, and 
disturbances in stopover areas may have com¬ 
pounding effects on populations. Rusty Black¬ 
birds are typically associated with wetland 
habitats throughout the annual cycle (Avery 
1995), but the core areas used by each of the 
three birds for stopover during autumn migration 
and by two birds during winter were in landscapes 
largely converted by agricultural use. Other 
researchers also occasionally found the species 
in agricultural fields primarily adjacent to wet¬ 
lands (Trautman 1940, Luscier et al. 2010). 
