Smith and Paton • SONGBIRDS SHIFT AUTUMN MIGRATION 
565 
can dictate the composition of species assemblag¬ 
es and number of individuals competing for 
resources at a given site. This can impact 
refueling performance, subsequent arrival and 
condition in wintering areas and, ultimately, 
survivorship (Bairlein and Hiippop 2004. Slokke 
et al. 2005, Gordo 2007). 
We documented interdecadal variation in three 
long-distance migrants (Common Yellowthroat 
[Geothlypis trichas |, Veery. Gray Catbird [Dume- 
tella carolinensis]) and two short-distance mi¬ 
grants (Ruby-crowned Kinglet. White-throated 
Sparrow [Zonotrichia albicollis]). Other variables 
not considered in our study could be more 
important than autumn temperature or annual 
capture rates for explaining long-term trends in 
these species. The unusual pattern observed for 
Gray Catbirds may be because some of the birds 
we captured are local residents in southern Rhode 
Island. Thus, opposing shifts among decades may 
be attributed to population fluctuations, as indi¬ 
cated by the relative importance of annual capture 
rate for explaining additional variation in mean 
capture dates in catbirds. 
Several species in our study (7 of 19) exhibited 
no significant long-term shifts in autumn migra¬ 
tion timing. For these species, it is difficult to 
disentangle whether birds are unable to adjust the 
timing of their migration (e.g., they rely heavily 
on endogenous cues unrelated to environmental 
variables), or whether shifts in migration timing 
were masked by other sources of variation that 
influence mean passage dates (Tottrup et al. 2006, 
Van Buskirk et al. 2009). Fluctuations in annual 
capture rates explained little variation in mean 
capture date and are unlikely to have influenced 
most species in our study (Miller-Rushing et al. 
2008). However, changes in annual capture rates 
or population sizes for two species, Ovcnbird and 
Northern Waterthrush. may in part explain the 
absence of long-term shifts in autumn timing. 
The influence of rising global temperatures on 
timing of autumn migration in North American 
passerines may be difficult to predict given the 
observed variation in the strength of response 
among species in different regions. The availabil¬ 
ity of long-term data sets limits analyses of 
phenological shifts to long-term banding opera¬ 
tions or study sites. However, more study is 
needed across a broader geographic scale, partic¬ 
ularly in coastal regions, and at different points on 
the migration route to accurately assess conser- 
vation implications and develop management 
strategies that address the impacts of phenological 
shifts in autumn migration. 
ACKNOWLEDGMENTS 
We are greatly indebted to 0. L. Kraus for his genero¬ 
sity and commitment to the study of migratory birds. We 
thank the Audubon Society of Rhode Island for property 
maintenance and housing at the Kingston Wildlife 
Research Station. We also thank S. R. McWilliams, J. E. 
Osenkowski. B. J. Pierce, and Lynn Duda for assisting with 
the banding operation and creating the electronic banding 
data base. 
LITERATURE CITED 
Bairlkin, F. and O. Hiippop. 2004. Migratory fuelling and 
global climate change. Advances in Ecological 
Research 35:33-47. 
Both, C., S. Bouwhuis. C. M. Lessells, and M. W. 
VisSER. 2006. Climate change and population declines 
in a long-distance migratory bird. Nature 441:81-83. 
Burnham. K. P. and D. R. Anderson. 2002. Model 
selection and multi-model inference: a practical 
information theoretic approach. Springer-Verlag, 
New York. USA. 
Cotton, P. A. 2003. Avian migration phenology and global 
climate change. Proceedings at the National Academy 
of Sciences of the USA 100:12219-12222. 
Gif.napp, P.. R. Leimu, and j. Merila. 2007. Responses to 
climate change in avian migration, time-microevolu¬ 
tion versus phenotypic plasticity. Climate Research 35: 
25-35. 
Gordo, O. 2007. Why are bird migration dates shifting? A 
review of wcathcT and climate effects on avian 
migratory phenology. Climate Research 35:37-58. 
Hkdenstrom, A., Z, Barta. B. Hei m, A. I. Houston. J. 
M. McNamara, and N. Jonz£n. 2007. Migration 
speed and scheduling of annual events by migrating 
birds in relation to climate change. Climate Research 
35:79-91. 
JENNI, L. and M. Kery, 2003. Timing of autumn bird 
migration under climate change: advances in long¬ 
distance migrants, delays in short-distance migrants. 
Proceedings of the Royal Society of London, Series B 
270:1467-1471. 
Leech. D. and H. Crick. 2007. Influence of climate 
change on the abundance, distribution and phenology 
of woodland bird species in temperate regions. Ibis 
149:128-145. 
Lehikoinen, E.. T. H. Sparks, and M. Zalakevicius. 
2004. Arrival and departure dates. Advances in 
Ecological Research 35:1-31. 
MacMynowski. D. and T. L. Root, 2007. Climate and the 
complexity of migratory phenology:: sexes, migratory 
distance, and arrival distributions. International Jour¬ 
nal of Biometeorology 51:361-373. 
MacMynowski, D., T. L. Root, G. Ballard, and G. R. 
Geupel. 2007. Changes in spring arrival of Nearctic- 
neotropical migrants attributed to tnultiscalar climate. 
Global Change Biology 13:2239-2251. 
