ALTENBURG JF & BOUDEWIJN TJ (2020) Barn Swallow Hirundo rustica predation by Tawny Owl Strix aluco. LIMOSA 93 (1): 15-22.

This paper describes effects of a Tawny Owl hunting inside a barn and repeatedly predating on adult Barn Swallows during the breeding season of 2019. Predation by the Tawny Owl took place around full moon, which likely resulted in higher light levels in some parts of the barn. The percentage of successful broods at this location was 50%: c. 30% lower than the five-year average for this site (2014- 18). The breeding success in 2019 at other Barn Swallow research sites in the region was almost 40% higher than at the predated location (Fig. 1). Only four of the 11 (colour-) ringed adult birds, which were identified at the start of the breeding season, were seen or retrapped after the predation events. Collected tail feathers in the barn indicated that at least seven adults had been predated. The length of the outmost rectrices and their white spot-lengths were used to sex the remains: one male and two females (Tab. 2). Four remains could not be assigned to a sex. Leaving behind intact tail and wing feathers of the predated adult birds may be characteristic for predation by Tawny Owls. One out of three females that had a second clutch after the predation incidents, changed nest location and partner, despite her ‘ex’ still being alive (Tab. 1). She returned to her former partner for her third attempt in another nest. A successful breeding male also changed partner after the predation events and had a second and third clutch with a second female. Switching of partners during the breeding season was not recorded at the other Barn Swallow research sites in the region. This Tawny Owl predation had significant effects on the breeding population and local reproduction, but can be qualified as a rare event.

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