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The Wilson Journal of Ornithology 123(1): 154_158, 2011 
Shift to Later Timing by Autumnal Migrating Sharp-shinned Hawks 
Robert N. Rosenfield , 1 - 5 Dan Lamers , 2 David L. Evans , 3 Molly Evans , 3 and Jenna A. Cava 4 
ABSTRACT.—Increasing proportions of Shar 
shinned Hawks (Accipirer striatus) migrated later 
autumn at the Hawk Ridge Bird Observatory, Dulut 
Minnesota during 1974-2009. Migration average 
about 4 days later over 35 years since 1974. and aboi 
days later during late September through October i 
the last 16 years of the study. Our results augme. 
previous findings demonstrating recent shifts in phene 
ogical events for birds. The proximate causes an 
potential consequences of this later timing of migratio 
1 Department of Biology, University of Wiscom 
btevens Point, WI 54481, USA. 
3 N4840 Foley Drive, Waupaca, WI 54981, USA. 
n , H ! W wI^ ge Bird ° bserv atory, 2928 Greysolon Ro 
Duluth, MN 55812, USA. 
5305^ USA 8473 Schndder Drive ’ Menomonee Falls, ’ 
Corresponding author; e-mail: rrosenfi@uwsp.edu 
should be investigated. Received 22 March 2010. 
Accepted 27 July 2010. 
Earlier timing of spring migration and egg- 
Jaying have been documented in relation to higher 
spring temperatures in a wide variety of temper¬ 
ate- zone birds in the Northern Hemisphere (e.g., 
Jenni and Kery 2003, Lyon et al. 2008, Miller- 
Rushing et al. 2008). Changes in bird migration 
times, with most attention on spring migration 
of passerines, are among the best-documented 
biological responses to increased temperatures 
(Miller-Rushing et al. 2008). 
Our objective was to investigate timing of 
autumnal migration of Sharp-shinned Hawks 
(Accipiter striatus) at Hawk Ridge Bird Observa¬ 
tory during 1974-2009. We chose the Sharp- 
