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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 123. No. 3. September 2011 
1 “ Tf d “ ,e f ° r ‘ hree l0 "8' dis ““ miS™« species and iwo sdon-distaw 
2 ,, a'g»n W.ldl.fe Researeh Sianon, Rhode Island, which exhibited non I,near relationships be<»» 
mode, selection following polynomial "" *” ,he ^ “*“* modd -* * 
study (Lehikoinen et al. 2004). while other 
European researchers reported mixed results 
(Sokolov et al. 1999. Jenni and Kery 2003, 
Tpttrup et al. 2006, Sparks et al. 2007), and some 
reported overall trends only towards advancing 
autumn migration (Cotton 2003. Thorup et al. 
2007). Thus, based on research conducted to date 
in North America and Europe, there are no 
consistent patterns in long-term trends in autumn 
migration of songbirds and the delays reported in 
our study are likely to be regionally specific. 
Explanations for the interspecific variation in 
autumn migration timing observed in European 
and North American studies have centered around 
species-specific traits. These traits include migra¬ 
tion distance or number of broods, time and 
energy required to complete molt prior to 
migration, and selective pressure for early arrival 
in wintering areas (Jenni and Kery 2003. Mills 
2005. Tottrup et al. 2006, Hedenstrom et al 
2007). The implications of climate-induced 
changes in timing of autumn migration are not 
as closely tied to breeding and reproductive 
success as shifts in spring migration. However, 
they may indirectly affect fitness and population 
stability because shifts in autumn passage dates 
