Click on any of the main images for a larger view

2 August 2012

What moult can tell us

We've seen in an earlier post (HERE) how the moulted feathers of adult birds at a nest site indicated that they had failed to breed this year. Another post (HERE) showed how we were able to age a one year old female. 

In this case, a known nest was visited in Co. Kerry two weeks ago where, unfortunately, no breeding had taken place in the nest box this summer. However, after checking the roost site in a blocked chimney in the same room of an old barn, this beautiful male was caught and ringed.

Male Barn Owl, Co. Kerry, mid-July (M.O'Clery).

The extended left wing of the same bird (M.O'Clery).

The left wing showing the numbered primary feathers (M.O'Clery).

Barn Owls have 11 primary flight feathers on each wing. Number 11 is tiny and is usually hidden under feathers near the leading edge of the wing. Primary number 10 is the first main flight feather, primary 9 the second and so on. In this photo, we can clearly see that primary 6 is just starting to grow. The original primary 6 would have dropped out, initiating the growth of a new one at the base of the wing. These primaries are replaced one by one so that at no point is the owl's ability to fly and hunt impaired.

Barn Owls leave the nest with a full set of fresh feathers, which they retain for a full year. After that, the wing feathers are replaced one by one, a few weeks apart, for the rest of their lives, so this bird is in his third year. Most Barn Owls don't survive in the wild more than 3 or 4 years, so this one can be regarded as something of a veteran. Let's hope he survives the winter and gets to breed again next year.