High mortality rate in a re-introduced grey partridge population in central Italy

Abstract

A radio-tracking study was carried out on a re-introduced population of grey partridges in a 10.6-km2 study area located in central Italy, in order to assess mortality rate and to evaluate the feasibility of carrying out large scale re-introductions of the species. Thirty-nine grey partridges were caught by live-traps during winter 2000 and equipped with backpack radio-transmitter. All released birds were offspring of partridges re-introduced previously on the study area and no significant differences were found in survival probabilities between sexes, age classes (juveniles or adults), and weight classes (<400 g or ≥400 g), with the exception of the juveniles-adult comparison with the weight class ≥400 g. Kaplan-Meier estimates give an average survival of 734 days (SE = 15.5). GLM analysis showed an overall interaction effect of the sex, age, and weight (P = 0.03). Mortality increased during the covey break up, if compared to other periods, although the differences were not significant; the same was for males, for adults, and for both weight classes, while significant differences resulted for female and juvenile survival rate among periods. Predation was the main mortality source for radio-tagged grey partridges (71.0%), followed by disease (25.8%). The high mortality rate found in our study could be explained in part with the origin of the population that was originally re-introduced using hand-reared grey partridges. Some important negative characters of reared birds, such as the poor anti-predator behaviour and the low diseases resistance, could carry over during the first and following wild generations. © 2002 Taylor & Francis Group, LLC.