Influence of fertilization and the concentration of antibiotics in the soil in the big river valley (NE Poland) on breeding success and condition of adult Red-backed Shrike <i>Lanius collurio</i>

Haematological indices are often used in ecology as indicators of environmental stress. The study investigated the relationship between fertilization types and antibiotic concentrations in the soil of grasslands and the breeding success and condition of adult birds. Significantly higher concentrations of antibiotics in the soil of cattle slurry-fertilized meadows and extensively managed meadows introduced into agri-environmental programmes, but located near a river, compared to mineral-fertilized meadows, were recorded. We suppose that the high accumulation of antibiotics in the soil of meadows close to the river is due to the transport of pharmaceuticals with water runoff in the flooded river valley. The haematological parameters (glucose, haemoglobin, haematocrit, eosinophils, basophils, monocytes, heterophiles, lymphocytes, H:L ratio), in contrast to the previously stated differences in their chicks, did not show significant differences between the types of meadows studied, which could result from a greater ability to maintain the body’s homoeostasis. Haemoglobin, basophil percentage, and H:L ratio were correlated with bird body condition and the distance of the territory from the river. Significant variation in breeding success was also found among the studied pairs of birds. Brood losses were more frequent in nests with higher H:L ratios of nestlings. The study suggests that intensive agricultural use, associated with the use of slurry and intensive use of pharmaceuticals in livestock lead to the accumulation of antibiotics in the soil, may affect their continued functioning and survival. The results highlight the need to address this issue in conservation programmes.