Northern Shrike (Lanius excubitor) Science Article 5
Great Grey Shrikes are usually territorial all the year round. However, flocks of up to 15 individuals have been observed on migration in Poland recently. On 3rd November 2001 in the morning, I observed a flock of 110 Great Grey Shrikes near ponds in Zimno (E Poland).
J. Michalczuk, BIOLOGICAL LETT. 2004, 41(2): 189n190