Demographic Parameters of the Grey Partridge (Perdix perdix L., 1758) in Upper Thracian Plain (Bulgaria)

The Grey Partridge (Perdix perdix) is a common gamebird which population decreased dramatically across Europe, including Bulgaria as well. While recent studies report continuing declines in numbers, sufficient data on basic demographic parameters of the species in Bulgaria are scarce or lacking. Main objective of the present study is to provide upto-date information on Grey Partridge demography in the arable lands of the Upper Thracian Plain (south Bulgaria). Breeding density was 6.27 ± 4.73 SD (min – max 0 - 20) pairs/km2 and density in August averaged 57.32 ± 41.82 SD (min – max 0 – 148.06) individuals/km2 during the monitored period (2018 - 2020). The Generalized Linear Model showed significant decrease of both breeding (Wald stat. = 65.47, p < 0.0001) and August (Wald stat. = 533.860, p < 0.0001) densities from west to east. However, direct reproduction parameters showed no geographic gradients and had relatively high mean levels as mean brood size was 9.0 ± 5.3 SD (min – max 1 - 26) young/successful pair (n = 163), chick survival rate up to six weeks of age was 0.56 ± 0.22 SD (min – max 0.19 – 0.94), brood production rate was 84.6 ± 20.9 SD (min – max 0 – 100%) and reproductive success was 3.96 ± 1.85 SD (min – max 0 - 8.5) young/adult bird. The present study shows highly unequal Grey Partridge breeding densities within the study area and suggests that diverse approach for management and restoration of the Grey Partridge will be needed across different parts of the Upper Thracian Plain.