Ringing birds at the nest gives valuable information about the young, such as their weight (and thus their state of health) as well as brood size (number of chicks) and their stage of growth. From this you can also work out the dates they hatched, and the dates the eggs were laid, all immensely important in trying to apply conservation measures for this secretive species.
Female Barn Owl in front of two chicks, at their nest, which is about a metre (3 feet) along a horizontal shaft of an old chimney system in a derelict house in Co. Kerry. The floor of the nest is covered in dried pellets of fur and bone which over time have actually formed a dry and insulated floor (Photo, taken under licence from NPWS: John Lusby).
Occasionally one or both Barn Owl adults will be caught at a nest, and in this case at a site in Kerry, the female was still attending the two chicks. She was carefully removed, along with the two chicks, for ringing. We had also caught and ringed a female at this site in 2011, but were a little surprised to find that this female was unringed, and therefore not the same which successfully reared two young last year.
Female Barn Owl wing showing uniformly aged flight feathers, indicating that she is one year old. You can click on the image for a closer view (Photo: M.O'Clery)
Feathers on Barn Owls are moulted (replaced) in a known sequence, and the main flight feathers only start to moult after their first year. In the photo, you can see that all the main flight feathers are of equal length and wear, so we can conclude that this female is one year old. In an older bird, there would be an obvious difference between one or more new feathers which would grow to replace older feathers.