Andreia Garcês and Isabel Pires

Europe is home to a diverse array of nocturnal bird species. Barn Owl (Tyto alba) and Tawny Owl (Strix aluco) are some of the most common nocturnal birds found across the European continent. Also, both species are the most commonly admitted as fledgling to Wildlife Rehabilitation Center. Many times, the age is difficult to determine. This mini guide provides a detailed methodology for determining the age of fledgling Strix aluco and Tyto alba in Europe, focusing on observable physical and behavioural characteristics. Both species exhibit distinct developmental stages that can be tracked through changes in plumage, size, vocalizations, and mobility. In the early stages, tawny owl fledglings are covered in fluffy white or grey down, transitioning to juvenile plumage around 4-5 weeks, while barn owl owlets also start with white down before developing their characteristic heart-shaped facial disc and more defined feathers. Behavioural cues such as begging calls and clumsy branch-hopping (branchers) indicate early fledgling stages, typically occurring at 3-5 weeks. By around 8-10 weeks, both species gain full flight capability and increased independence, although they continue to rely on their parents for food. This compilation includes visual aids and growth charts to assist with age estimation, providing a practical tool for biologists, veterinarians, ornithologists and bird watchers.

DOI: 10.22271/23940522.2024.v11.i6a.1056

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