AN ANALYSIS OF UNUSUAL FLIGHTS OF NEOTROPICAL MIGRANTS TO NORTHEASTERN NORTH AMERICA 
Figure 8. A Scarlet Tanager on 8 April 2009 in Rochester, Massachusetts was part of the second fallout In that month, which included 
more tanagers (and larger Neotropical migrant species generally) than smaller taxa, such as warblers and Passerina buntings, which 
were predominant in the earlier fallout. Photograph by Pearl Thompson. 
the ocean, the survivors only regaining land 
far to the northeast on 4 April. Most of the 
overshooting species detected on 4-7 April 
were smaller birds: 23 Indigo Buntings and 11 
warblers, compared with 14 larger species in 
total (Eastern Kingbird, Gray Catbird, Blue 
Grosbeaks, Scarlet and Summer Tanagers, 
Purple Martins). In particular, the ratio of In- 
digo Bunting to Summer Tanager (3.3:1) was 
similar to those in the southeastern United 
States between 25 March and 15 April (Figure 
2, 6.5:1) and during the breeding season in re- 
cent years (4.5:1 during 2005-2007 in the 
Eastern Breeding Bird region; Sauer et al. 
2008). This suggests that the smaller and larg- 
er species suffered similar mortality en route. 
The reversed ratio of Indigo Bunting to 
Summer Tanager during 8-11 April might in- 
dicate that the birds had left on favorable 
winds on the evening of 6 April — the tanagers 
from northern South America, the buntings 
from Caribbean islands (Figure 7). However, 
the greater prominence of larger birds (12 
Summer Tanagers, three Scarlet Tanagers 
(Figure 8), one Rose-breasted Grosbeak, and 
three Blue Grosbeaks, one Eastern Kingbird, 
one Gray Catbird, one Purple Martin versus 
just two vireos, three warblers, and hve Indi- 
go Buntings) could also reHect greater mortal- 
ity of smaller species during a longer flight 
over open ocean (cf. Figures 6, 7). A dead 
Kentucky Warbler was found 6 April in Nova 
Scotia, but three Summer Tanagers died after 
being found 8 April in Nova Scotia, and a 
dead Hooded Warbler was found 9 April in 
Massachusetts. 
Male passerines are thought to be “time op- 
timizers” that make long-distance flights to 
get to the breeding grounds rapidly and ahead 
of females for choice of territories; where 
specified, almost all the birds in the present 
fallouts were males. It is sometimes suggested 
that overshooting migrants have simply mis- 
judged the distance of goals along their cor- 
rect flight directions or that these birds are ac- 
tively seeking out territories beyond the 
northern fringes of breeding range. As noted 
earlier, southwestern airflow in spring in east- 
ern North America and along the East Coast 
is also thought to abet this misjudgment. The 
pattern of airflow around large low-pressure 
systems in central and eastern-interior North 
America (Figures 6, 7), however, suggests 
that unusually early events may involve much 
greater displacement — flights over the ocean 
from areas much farther to the south than has 
been generally surmised. 
There also has been much speculation on 
the subsequent fate of such displaced birds, 
but few data exist to support suppositions 
about the extent of mortality among these 
birds. An interesting feature of timing and 
distribution of Indigo Buntings (Figure 2) 
was the apparent shift in the proportions of 
buntings; in Nova Scotia and elsewhere 4-5 
April, they were roughly evenly distributed, 
but during 6-7 April, they were noted exclu- 
sively in New Brunswick and Maine, includ- 
ing one well inland. This suggests that some 
birds undertook corrective southward move- 
ments after their considerable displacement 
in the 4 April fallout. A similar movement 
was indicated after a large fallout of “reverse 
migrants” in southwestern Nova Scotia in ear- 
ly October 1998 (McLaren et al. 2000). 
The extreme displacement and restricted 
geographical distributions of the birds in 
these events offers an unusual opportunity for 
further detailing of the meteorological cir- 
cumstances, geographical origins, and flight 
behaviors of successful birds using modern 
techniques of individual-based and spatially 
explicit migration models. Such an analysis is 
being undertaken by the junior author, for 
publication in the technical literature. 
Acknowledgments 
We are grateful to R A. Buckley, Ken Knowles, 
Marj Rines, Eric Saltzman, and Angus Wilson 
for clarifying places and dates of some of the 
birds reported on the Internet. Brian L. Sulli- 
van helped with use of eBird data. Eric Mills, 
P. A. Buckley, and Alvaro Jaramillo made 
many helpful suggestions on successive 
drafts. The first author has also benefited 
from exchanges with Will Russell on various 
aspects of avian vagrancy. 
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