| Summary: | The Great Grey Shrike Lanius excubitor, as well as other species of family Laniidae, re-cognise humans as potential predators and actively defend nests. During an intensive study in western Poland we examined the influence of observer visits on breeding success and breeding behaviour of the Great Grey Shrike. We compared changes in nest position of pairs that were disturbed with those that were not disturbed. We did not found a nega-tive impact of nest visits or the frequency of nests visits on the breeding success of Great Grey Shrikes. However, pairs with disturbed nests in one year significantly increased nest height in the following breeding season. In contrast, there was no significant change in nest height change in pairs which were not disturbed in the previous season. These find-ings suggest that even a short-term increase in predation risk due to a visit by an observer appears to trigger an adaptive anti-predator response. The results indicate that shrikes re-cognise humans as potential predators and are able to predict the probable return of preda-tors even the next season. This result is interesting, because birds have reacted, clearly purpously, by heightening their nests after intrusion of a ground predator.
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