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An Analjfsis of Unusual Flights 
of Neotropical Migrants to north- 
eastern North America in April 2009 
IAN A. MCLAREN • BIOLOGY DEPARTMENT, DALHOUSIE UNIVERSITY, HALIFAX, NOVA SCOTIA B3H 4J1 • (CORRESPONDING AUTHOR; EMAIL: IAMCLAR@DAL.CA) 
JAMES D. MCLAREN « INSTITUTE FOR BIODIVERSITY AND ECOSYSTEM DYNAMICS, UNIVERSITY OF AMSTERDAM, 1018VYV AMSTERDAM, NETHERLANDS 
An Incandescent bird in a mostly leafless early April landscape, this Prothonotary Warbler at Winter Harbor, Maine 4 April 2009 was among the first signs of an unusual very early "fallout" of Neotropical 
migrants from New York and New England to Atlantic Canada. Photograph by Nathaniel Child. 
Abstract 
Wind patterns are often invoked in a general 
way to help explain mass arrivals (fallouts) of 
spring migrants and the premature appear- 
ance of migrants and of vagrants well beyond 
their normal breeding ranges (overshoots). 
Two exceptionally early fallouts of overshoot- 
ing Neotropical migrants and vagrants in 
northeastern United States and Atlantic Cana- 
da, beginning 4 and 8 April 2009, were ap- 
parently caused by displacement far over the 
Atlantic Ocean of migrants crossing the Gulf 
of Mexico and Caribbean Sea as a result of 
deep and extensive low-pressure systems 
moving slowly northeastward in the middle 
of the North American continent. There were 
indications of different geographic origins of 
birds involved in the two fallouts, some high- 
er mortality among smaller species, and some 
later correction for migratory displacement. 
Background 
During mid- to late afternoon of 4 April 2009, 
four unexpected Neotropical migrants — a Yel- 
low-throated Warbler, a Worm-eating War- 
bler (Figure 1), and two Indigo Buntings — 
were found in Nova Scotia and reported by 
the few observers active on a day with fog, 
bouts of rain, and southerly to southeasterly 
winds (see Table 1 for scientific names of 
species frequently noted in the text). The 
bunting is rare but regular in April (usually 
later), with only one confirmed nesting 
record in the province, whereas the warblers 
were earlier than any previously recorded and 
well beyond their regular breeding range lim- 
its in New Jersey and southern Massachu- 
setts, respectively. The reports encouraged 
more searching next day, and observers found 
five more Indigo Buntings, an Eastern King- 
bird, and two Purple Martins, both abnormal- 
ly early, as well as a Hooded Warbler and a 
Summer Tanager, which breed regularly north 
to Massachusetts and New Jersey, respective- 
ly. During the next two days, there were only 
four new finds, including a recently dead 
Kentucky Warbler, a species that nests north 
to Connecticut. Then, beginning 8 April, a 
new wave of early migrants and vagrants was 
detected, this time predominantly composed 
of Summer Tanagers. Birds that arrive excep- 
tionally early in spring or beyond their nor- 
mal breeding range, or both, are often termed 
“overshoots,” a term we will continue to ap- 
ply, but there has been much confusion in the 
literature regarding the mechanisms that pro- 
duce such arrivals (see Brinkley 2001 for a 
terminological review). 
Such early and northerly spring arrivals 
have been linked to weather patterns in sev- 
eral essays in the past. Bagg et al. (1950) re- 
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NORTH AMERICAN BIRDS 
