Effect of Management of Grassland on Prey Availability and Physiological Condition of Nestling of Red-Backed Shrike Lanius collurio.

Simple Summary: The decline in biodiversity in agricultural areas in much of biological Europe is linked to agricultural intensification and land use changes. Bird species inhabiting natural and semi-natural grassland are among the most endangered ecological groups in Europe. This study aimed to determine the impact of grassland use on the availability of arthropods for red-backed shrike Lanius collurio and the condition of their chicks. A total of 133 pastures with different types of use were delineated: 1. extensively used meadows, 2. intensively used meadows fertilised with mineral fertilisers, and 3. intensively used meadows fertilised with manure. The analyses also took into account environmental factors that can affect food availability and condition parameters of chicks (distance to the forest, distance to the river, soil moisture, and proportion of shrubs and tree stands in the meadow border zone). The diversity of arthropods was greatest in extensively used meadows, and the average abundance and proportion of invertebrates over 1 cm in length was highest in intensively used meadows, especially those fertilised with manure. Coefficients characterising body condition parameters (resBCI) and glucose levels of nestlings associated with breeding birds foraging in extensively used meadows indicate good nutrition, but blood parameters suggest severe environmental stress, as is the case in the intensively used meadows fertilised with manure. The study aimed to determine the influence of grassland management on the potential food base of the red-backed shrike Lanius collurio and the condition of chicks in the population inhabiting semi-natural grasslands in the Narew floodplain. The grassland area was divided into three groups: extensively used meadows, intensively used meadows fertilised with mineral fertilisers, and intensively used meadows fertilised with liquid manure, and selected environmental factors that may influence food availability were determined. Using Barber traps, 1825 samples containing 53,739 arthropods were collected, and the diversity, abundance, and proportion of large arthropods in the samples were analysed depending on the grassland use type. In the bird population, the condition of the chicks was characterised by the BCI (Body Condition Index) and haematological parameters (glucose level, haemoglobin level, haematocrit, and H:L ratio). The diversity of arthropods was highest in extensively used meadows. Still, the mean abundance and proportion of arthropods over 1 cm in length differed significantly for Orthoptera, Hymenoptera, Arachne, and Carabidae between grassland use types, with the highest proportion of large arthropods and the highest abundance recorded in manure-fertilised meadows. The highest Body Condition Indexes and blood glucose levels of nestlings indicating good nestling nutrition were recorded in nests of birds associated with extensive land use. The H:L ratio as an indicator of the physiological condition of nestlings was high on manure-fertilised and extensively managed meadows, indicating stress factors associated with these environments. This suggests that consideration should be given to the effects of chemicals, such as pesticides or drug residues, that may come from slurry poured onto fields on the fitness of red-backed shrike chicks. [ABSTRACT FROM AUTHOR]