AN ANALYSIS OF UNUSUAL FLIGHTS OF NEOTROPICAL MIGRANTS TO NORTHEASTERN NORTH AMERICA 
Figure 3. Summer Tanagers were prominent in the second wave of early and vagrant 
Neotropical migrants that first arrived 8 April 2009 in Nova Scotia. This male at Mor- 
den was found 8 April but perished the next day. Photograph by Gary Myers. 
birds and meteorological circumstances. 
Composition and 
timings of the fallouts 
The dates of discovery of early Neotropical mi- 
grants and vagrants from Atlantic Canada to 
New Jersey were obtained from birding mail- 
ing listserves, and some of these reports were 
clarified by the authors’ direct contact with re- 
gional observers. Some other Neotropical mi- 
grants that normally migrate in early April 
(e.g., Barn Swallow, Hinmdo rustica) or also 
winter widely in the southern United States, 
(e.g., Palm Warbler, Dendroica palmanim) had 
previously begun to appear in inland and 
northeastern states and are not considered 
here. A few scattered individuals of normally 
later-migrating Neotropical migrants were also 
reported by late March on birding mailing list- 
serves for the interior United States and/or 
along the Atlantic coastal states north of Flori- 
da, and individuals of Northern Panda (Panda 
americana') , Scarlet Tanager, and Indigo 
Bunting had been found up to si.x days prior to 
4 April as far north as Massachusetts. These 
clearly did not form a coherent wave of 
Neotropical migrants moving northward prior 
to the events considered here. Although more 
unusually early migrants and vagrants were 
found in the region after mid-April (especially 
beginning 22-23 April in Nova Scotia), others 
had lingered from early April (notably Indigo 
Buntings, tanagers, and grosbeaks at feeders), 
making later patterns of arrival less easily dis- 
cernable. Accordingly, we restricted our survey 
to 4-1 1 April, that is, up to three days after the 
start of the second fallout. 
There were two clear peaks of arrivals (Fig- 
ure 2). Beginning 4 April and continuing next 
day, 14 individuals of seven species were 
found in Nova Scotia and 23 individuals of 
nine species elsewhere, predominantly Indigo 
Buntings overall. During 6-7 April, only six 
new individuals were found in 
Nova Scotia (including a Pur- 
ple Martin on Sable Island, the 
small arc above the insert box 
on Figure 2), none of them In- 
digo Buntings. By contrast, the 
14 new individuals to the west 
and south included six Indigo 
Buntings. Then, beginning 8 
April through next day, more 
new birds were found in Nova 
Scotia (14 in total, including 
eight Summer Tanagers), and a 
Summer Tanager, a Rose- 
breasted Grosbeak, and a Blue 
Grosbeak even reached the 
southeastern coast of the New- 
foundland; the hrst and last 
were the earliest of those rare vagrants ever 
recorded there. During the same interval, only 
nine new birds (and only one Summer Tanag- 
er) were found from New Brunswick south to 
New York. Only a few more individuals were 
added during the next two days. 
The number, variety, and especially the tim- 
ing of migrant and vagrant Neotropical passer- 
ines in Atlantic Canada and the northeastern 
United States in early April were unusual. 
There were no concentrations of these species 
moving northward in the United States prior 
to 4 and 8 April, which therefore presumably 
represent the two dates of arrivals of most or 
all the birds from more distant sources. The 
hrst fallout was more evenly distributed be- 
tween Nova Scotia and coastal regions to the 
south and west, and Indigo Bunting was the 
dominant species. The second was more pro- 
nounced in Nova Scotia than elsewhere (and 
reached Newfoundland) and was dominated 
more by Summer Tanager (Figure 3). These 
different species compositions and distribu- 
tions suggest that the two events were influ- 
enced by different geographical origins and 
different meteorological patterns. 
Neotropical migrants in 
probable source regions 
Because electronic sources under-report rou- 
tine birds and do not include measures of 
searching effort, we relied more heavily on 
data provided by the North American Avian 
Knowledge Network (AKN) (<http://www. 
avianknowledge.net/content>). This open-ac- 
cess site systematizes checklists submitted by 
Figure 4. Numbers of Indigo Bunting and Summer Tanager counted per hour by birders submitting lists of all species in coastal states 
of the southeastern United States between 20 March and 15 April 2009. The counts from Louisiana, Mississippi, Alabama south of 31 ° 
N and the Florida Panhandle west of 83° W are combined as "Gulf Coast." 
Figure S. Nexrad images at times of early flights of night migrants preceding the fallouts of 4 and 8 April. Images from <http://weather. 
noaa.gov/radar/mosaic/DS.p19rO/ar.us.conus.shtml>. The color scales on the original images were converted to a comparable grayscale. 
There was little or no rain in the region during these evenings. 
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NORTH AMERICAN BIRDS 
