Ornis Hungarica. vol.12-13. (2003) p.223-229.
Which method is most suitable for censusing breeding populations of red-backed (lanius collurio) and great grey (l. Excubitor) shrikes?
1. Introduction Up to now, studies have shown that it is very difficult to estimate accurate numbers of shrike (Lanius spp) breeding pairs. During our shrike biology research in Western Poland this problem was evident. Actual breeding pair numbers were derived from a combination of special counts in the pre-breeding period, intensive nest searches and colour ringing. Empirical tests have shown point counts and line transect methods, with regard to Red-backed (Lanius collurio) and Great Grey (L. excubitor) Shrike population size estimates, to underestimate numbers severely. Furthermore, we have found that the 'improved mapping technique' underestimates the actual numbers of Red-Backed Shrike breeding territories by as much as 45-80%. It underestimates the actual numbers for the Great Grey Shrike by just under 40%. In the case of the Red-Backed Shrike, the accuracy of results from the 'improved mapping technique' was negatively correlated with the population density. However, we did manage to achieve accurate numbers of shrike breeding pairs, but only by using specific methods. For the Great Grey Shrike, counts during pair formation period yielded the most precise results and for the Redbacked Shrike, intensive nest searches proved to be the most effective method.