O’Brien and Rit chi son • NON-BREEDING ECOLOGY OF SHRIKES 
365 
and migrant Loggerhead Shrikes wintering in 
northeastern Mexico using stable isotopes and 
found residents occupied areas with more bare 
ground than areas occupied by migrants. If this 
difference results from competition between 
residents and migrant shrikes, assuming residents 
occupy more optimal habitat and bare ground is 
in important measure of habitat quality, these 
results suggest availability of optimum habitat 
may be limited and could affect over-winter 
survival (Perez and Hobson 2009 ). 
Mortality .—Two of eight radio-marked shrikes 
in our study were apparently killed by hawks; 
other investigators have also noted that shrikes 
may be vulnerable to hawk predation. For 
example. Walter (1979) reported that Eleonora’s 
Falcons (Falco eleonorac) prey on birds migrat¬ 
ing across the Mediterranean Sea, and an 
estimated 15-20% of all birds taken are shrikes 
(Red-backed Shrikes \L. colliirio], Lesser Grey 
Shrikes [L minor], and Woodchat Shrikes [L. 
senator]), Cade (1995) suggested shrikes may be 
particularly vulnerable to predators because they 
are not very maneuverable in flight. Their 
relatively poor flying ability, in combination with 
conspicuous plumage, may make shrikes attrac¬ 
tive targets for predators (Yosef 1994). Vulnera¬ 
bility to hawk predation may be contributing to 
the decline in shrike populations. 
ACKNOWLEDGMENTS 
We thank Brian Davidson. Matt Thomayer. Gabc 
lenkins. Ryan Dunbur, Nicole Beaver, Emily Clemons. 
Sara Asher, and Carrie Slone for assisting with the field 
*° r k, C. E. Braun and two anonymous reviewers for 
helpful reviews of our manuscript, and the Kentucky 
Department of Fish and Wildlife Resources for financial 
support 
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