SHORT COMMUNICATIONS 
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FIG. 1. Number of nocturnal flight calls of Pine Siskins detected at three sites near Gardiner, Maine during 10-16 
October 2008, by hourly interval (EST). Sunrise occurred at 0551 hrs EST. 
conditions of food shortage which induce long¬ 
distance migratory movements similar to those 
seen in determinate long-distance migrants (Ho- 
chachka et al. 1999). There was an unusually large 
migratory irruptive event for Pine Siskins during 
the 2008-2009 season, especially in the eastern 
United States. The average flock size reported by 
Project FeederWatch participants in the eastern 
U.S. doubled from the prior year’s migration (7.2 
to 15.5), and the number of feeders visited 
increased by 31% (D. N. Bonter, pers. comm.). 
Data from eBird across —480 sites in Maine, New 
Hampshire, Vermont, and Massachusetts showed 
a detectable pulse in the frequency of checklists 
reporting Pine Siskins in the second week of 
October 2008 from 1.7% in week one to 11.2% in 
week two and 7.1% in week three (eBird 2010). 
This pulse corresponded with the period when we 
detected Pine Siskin night flight calls suggesting 
that a broad-scale migratory movement of the 
species was underway across New England. The 
frequency of 11.2% in the second week of 
October 2008 was the highest observed for Pine 
Siskins in October since 2001 (eBird 2010). 
Another irruptive cardueline finch that occurs 
in North America, Common Redpoll, has been 
heard migrating nocturnally in Greenland and 
Eurasia (Knox and Lowther 2000), but there are 
few data on the extent and timing of this behavior. 
These and our observations suggest this is a rare 
behavior among finches. Future study of nocturnal 
migration during irruptive years could help 
explain if nocturnal migration is a plastic behavior 
induced under conditions that lead to broad scale 
TABLE 1. Number of Pine Siskin flight calls detected per night at each of three sites near Gardiner, Maine from 10 to 
16 October 2008. Recordings were not made at all sites on all nights, as indicated by N/A . 
Site io Oct 11 Oct 12 Oct _ 13 Oct _ \A Oct _ 15 Qct _ 16 Uct 
1 28 0 0 0 11 80 N/A 
2 2 16 3 0 N/A N/A N/A 
3 N/A 1 0 0 0 50_4 
