Potential effects of avian predators on the behaviour of the Little Bustard Tetrax tetrax during the display season in a cereal pseudo-steppe

Abstract

The Little Bustard Tetrax tetrax is an endangered steppe bird whose last remaining breeding populations in Catalonia (NW Spain) are located in the Lleida plains. Although the decline in this population is mainly associated with habitat loss and degradation due to agricultural intensification and urban encroachment, the proliferation of predators, some favoured by hu- mans, may also be having negative effects on this population, either through direct predation or indirect effects on behaviour and survival. Here, we describe the type of behavioural response exhibited by Little Bustards during the display season when they encounter a potential avian predator and discuss the possible indirect effects of these interactions. During counts carried out in the springs of 2010–2022 in three Special Protection Areas in the Lleida plains, 88 encounters between Little Bustards and eight species of avian predators were recorded. Among them, the Western Marsh Harrier Circus aeruginosus, Montagu’s Harrier C. pygargus and the Yellow-legged Gull Larus michahellis were the most frequent species involved in these encounters, although only the Yellow-legged Gull conducted deliberate attacks in a consistent way. Irrespective of the predator or its attitude, most encounters resulted in the Little Bustard being flushed. The number of encounters were higher at the beginning of the mating season, which may prevent Little Bustards from settling in otherwise suitable areas of habitat. The flushing of the bustards may increase the risk of collision with power lines and reduce mating success. Since the number of encounters between Yellow-legged Gulls and Little Bustards seems to have increased in recent years in the study area, we believe that there is a need to conduct further studies to understand how these interactions affect the population dynamics and conservation of this endangered species.