Effect Great Grey Shrike on lizardpopulation On the dry heathland where the authors have a plot for monitoring reptiles, they also study the Great Grey Shrike (Lanius excubitor). The shrike usually arrives in its winter territory from about 1st October, leaving at the beginning of April. It has a habit of storing any prey that it does not eat immediately, such as lizards, in larders. The Viviparous Lizard (Zootoca vivipara) is the only species of lizard present. All 72 lizards found in larders during the winter of 2011 – 2012 were adult males. Female lizards appear later after the shrike has left. From two time-budget studies, it appeared that the Great Grey Shrike may eat 18 lizards a day. It is estimated that during its whole stay, a shrike may catch at least 250 lizards. In order to obtain an impression of the influence of a shrike on the population of Viviparous Lizard, an extra count was carried out. About one half of the monitoring route ran through the main hunting area of the shrike. The co-ordinates of the lizards were recorded with GPS. In Figure 6, the route is shown as a blue line and the main hunting area by the broken red line. The locations of the lizards counted are represented by yellow thumbnails. The lizards found in larders in 2011 – 2012 are represented by thumbnails, green for the shrike that was present till 27th March and blue for one that arrived on 26th March. Only 4 out of 28 lizards counted were present within the core hunting area of the shrikes, showing that the Great Grey Shrike has a considerable effect on the number of lizards, in particular the males.