Birds of Ireland: Rook
Rooks collecting nesting material
Rooks are around 43–47cm long with a wingspan of 88–92cm
They are a common breeding species found here all year round — typically on farmland or in suburban/urban areas.
Rooks are slightly bigger than a jackdaw. They have black plumage with a purple-blue sheen, and their feathers are duller and browner when worn. They have a long, conical, slightly downcurved beak and black legs.
The outer half of adult rooks' beaks are dark and the inner half/ and their bare throat patch is powdery-white. They have untidy-looking feathers around their thighs (like ‘shaggy trousers’). Rooks move slowly/deliberately on the ground, and ‘gallop’ away if approached.
Juvenile and immature rooks in their first year have an all-black beak; and black feathers on the inner half of their upper mandible In flight, rooks appear all dark; their primaries are clearly seen as ‘fingers’ at end of wings — these are not so noticeable on jackdaws.
A rook's voice is a typical which can be repeated several times; they often fan their tail and stretch forward when calling.
Bird identification would be very easy if each bird species had the same plumage colour and pattern all the time. What can make birdwatching a challenge for even the most experienced birdwatcher is feather moult, that process by which birds change plumage from juvenile to adult, from breeding to non-breeding and all stages in between.
A very important part of bird identification is being aware of and understanding the basics of feather moult. Feathers must be strong, light and flexible to do their work. Without them, birds cannot fly or stay warm.
Like mammals shedding old hairs as new ones grow, birds replace old feathers with new ones regularly. However, unlike humans, who shed hair continuously, birds generally replace their feathers only at certain times of the year.
Birds have also evolved a system of replacing or moulting feathers in sequence to ensure that feather function is maintained. The main flight feathers, the primaries and secondaries, are usually replaced in a predictable sequence, starting with the innermost primary and continuing outward from the body, while the outermost secondary is first replaced, continuing inward towards the body. The new feathers grow in place of the old ones, pushing them out. This results in gaps where the old feathers have dropped off and the new ones are not yet fully grown, most evident on the wings and tail.
Most land birds moult in such a way that they are always able to fly. In late June and July crows have their wings and tails in moult, with some individuals flying around almost tailless and with many wing feathers missing but still enough to stay airborne.
On the other hand, ducks, swans and geese moult all of their flight feathers at the same time and as a result are flightless for 4-6 weeks.
- Jim Wilson is a wildlife writer, broadcaster, tour leader, and former chairman of BirdWatch Ireland. He has been involved in the study and conservation of birds in Ireland for more than 45 years, contributing to several major surveys and international projects.
- Mark Carmody is an award-winning wildlife photographer, has a PhD in biochemistry and works as a European patent attorney.
