Like most words, they mean what is generally accepted. If there is doubt, then define the use in the communication. There is a pretty strong hint in all the
preceding that the term fledging (in various forms) does not apply at all well to birds that hatch in a developed state and able to leave the nest on day one. Such as the rails as you mention, and many others. There is also the complication that arises when
you try to define words that some of these birds the chicks are able to feed themselves and others the parents feed them, even if they are equally active at hatching. The word is best used for those birds that stay in the nest for weeks, as chicks (nestlings)
and when they leave the nest are fledglings. In some, leaving the nest that can be an immediate one off event, in others that process by itself can take several days. That was Martin’s question. I still believe the word origin is from having grown feathers
as in “fully fledged” will mean lost down and covered in feathers, even though I support the functional use as having left the nest.
Philip
From: John Harris [
Sent: Sunday, 13 November, 2016 2:20 PM
To:
Subject: Re: [canberrabirds] What is meant by fledging?
When does the precise definition of ‘fledged' matter and when does it not matter? How much does it matter, for example, when reporting on eBird? I have recently reported
Coot chicks and chose FL, the only sensible Breeding Code for Coot chicks swimming around near their parents. I did not see them being fed but if I had, and if I had therefore used the code FY, does that matter to anybody? Does anyone ever do such fine-grained
research on eBird data or is the fact of a confirmed breeding event all that really matters? For a water bird chick swimming, there is actually no higher code than FL and so I don’t imagine that the amount of down etc matters.
On the other hand, last year Julie Clarke made some amazing observations and photos of Buff-banded Rail breeding in Forde Creek. She and I wrote a paper on it which was published
by Australian Field Ornithology. In this case the meaning of ‘fledged’ and other technical descriptive words became potentially very important. For us, this was the most difficult part of the paper. It was one thing to have field notes and photos but quite
another to use technical terminology correctly. Over more than a month, chicks covered completely in down developed juvenile plumage which gradually developed into adult or near-adult plumage. But to divide these up into distinct stages was impossible. We
avoided the word fledgling as unhelpful. If a chick with down was a fledgling, then began to grow flight feathers and then became a juvenile with juvenile feathers but had not yet flown, was it still a fledgling during all that development? Or, as some definitions
would have it, did it only become a fledgling at first flight? In the end, the word ‘fledgling’ was too vague and ill-defined for us amateurs.
That is very strange to have “the fledging period is the interval between hatching and flight'
as that would put fledging at starting at the time of hatching. It also gives a difference of
nestling period
and the fledging period
as only whatever the difference may be between and departure from the nest
and
flight.
Philip
From: David McDonald (personal)
Sent: Saturday, 12 November, 2016 3:03 PM
To:
Subject: Re: [canberrabirds] What is meant by fledging?
In eBird Australia, the breeding cum breeding behaviour code 'FL Confirmed--Recently Fledged young' is defined as 'Recently fledged or downy young observed while still dependent upon adults', see
http://help.ebird.org/customer/en/portal/articles/1006850-breeding-codes-behavior-codes?b_id=1928&t=412380 . I imagine that it maps well to COG's code DY = dependent young.
An authoritative source, Gill, FB 2007, Ornithology, 3rd edn, W.H. Freeman and Co., New York, NY, states, at page 491, 'Technically speaking, the nestling period is the interval between hatching and departure from the nest, and the fledging period is
the interval between hatching and flight'. This definition is sourced to Skutch AF 1976,
Parent birds and their young, University of Texas Press, Austin.
Gill goes on to write: 'The nestling and fledging periods may be the same for some altricial birds, such as hummingbirds, but different for subprecocial and precocial birds, which have short nestling and long fledging periods. The moment of departure from
the nest by altricial birds is commonly term fledging even though the young birds may only flutter and scramble about for a few days before the first flight'.
Definitions (p. 471):
- Altricial: Naked, blind, and helpless at hatching.
- Precocial: Hatchlings leave the nest immediately (nidifugous) and follow their parents; pick up their own food soon after hatching, although parents help to locate food.
- Subprecocial: Hatchlings leave the nest immediately and follow their parents; are fed directly by their parents.
Also
- Superprecocial: Wholly independent.
- Semiprecocial: Hatchlings are capable of body temperature regulation; mobile but stay in the nest; fed by the parents.
- Semialtricial: Hatchlings stay in the nest (nidicolous), although physically able to leave the nest within a few hours or the first day; fed and brooded by parents.
Geoffrey may care to launch a quiz for us to identify examples of Canberra region birds that fit into each of the six 'development categories of hatchlings', as Gill puts it.
David
On 11/11/2016 9:10 AM, Martin Butterfield wrote:
In the past I have come across two definitions:
-
a young bird leaving the nest ; and
-
a young bird taking its first flight.
Some people have said there is no difference between the 2 definitions.
This morning at 0530 the male adult was not in the nest and both chicks were vigorously flapping their wings. However take off did not happen, and Dad returned shortly thereafter. At about 0830
this was the situation.
The more adventurous chick is clearly out of the nest. It still hasn't flown but in the last 10 minutes there has been much stretching of wings. On past experience the business of walking up and down a branch
could go on for a couple of days, sometimes both chicks and Dad taking a stroll. I don't believe they have yet fledged.
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