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No abstract

Habitat degradation caused by feral grazers has been identified as a possible limiting factor for the endangered San Clemente Loggerhead Shrike ( Lanius ludovicianus mearnsi). In 1999, we installed supplemental foraging perches within shrike breeding territories on San Clemente Island and observed shrike foraging behavior before and after perches were installed. Shrike foraging efficiency, determined by measuring foraging attack distances and success rates, was not improved when supplemental perches were present; however, shrikes shifted their focal foraging sites to areas where perches were installed. Shrike home ranges did not change size when supplemental perches were installed, indicating that foraging areas made available by adding supplemental perches were not of higher quality than those that were previously available. However, the addition of supplemental perches may have increased the total foraging habitat available to this endangered subspecies.