Koreelah NP: Sorting out the fairy-wrens. Part 2, The young males
Part 3 on the wrens at Koreelah can be found here.
For male fairy-wrens the changes in plumage colour are much more complex than for the females.
Juvenile males initially look just like the females. The first thing to change is the tail colour. Wikipedia says that young male superb fairy-wrens "usually develop a blue tail before their first winter".
And then they begin to acquire a dark beak. The photo on the left shows a young male superb wren with blue in its tail, and dark colouring at the tip of its bill while the rest of its bill is still orange. It also still retains the orange-coloured eye-ring and lores.
With the beak only partly coloured, they begin to lose that orange colour from the eye-ring and lores, and their legs become dark, as shown in the photo on the right.
It is likely that variegated wrens would follow a similar sort of progression. Wikipedia says that young male superb fairy-wrens develop black bills after their first winter, but immature variegated wrens "will develop black bills by six months of age".
So the young male superb and variegated wrens adopt "eclipse plumage", which is mostly brown on top, with paler colour on their undersides, dark beaks and legs, and bluish colour in their tails, as shown in the photos on the left.
At this stage it is easy to tell them apart from the females and juveniles, but difficult to distinguish between males of the two species.
With individual differences between birds, having looked through my own photos, and photos on the internet, I think the most reliable way of telling the eclipse males of these two species apart is to look at their eye-rings. Variegated wrens in eclipse plumage have a complete ring of pale feathers around their eyes, while superb wren males in eclipse plumage have only half a ring, beneath the eye.
Male fairy-wrens of these two species moult out of their eclipse plumage in their first spring.
Lynx Ed says "A pre-breeding partial moult of most body feathers occurs in late winter or early spring. In the case of males, the Dull plumage of the non-breeding season is replaced completely or partly by the Bright plumage of the breeding season. The onset of this moult, which lasts for about a month, varies according to age, social status and condition, younger males beginning in August or September and older, more dominant ones starting as early as April in southern Australia".
The same website also says that young male superb wrens acquire almost their complete breeding plumage at this time. However the moulting into breeding plumage may be patchy in the first two or three years.
With variegated wrens, the Gaia Guide website says they "moult into breeding plumage the first breeding season after hatching, though this may be incomplete with residual brownish plumage and may take another year or two to perfect". Subordinate male variegated fairy-wrens may retain a brown patch in the midst of the blue feathers at the top of their heads until they are about four years old.
As long as they have some of their blue feathers it is usually easy to tell the two species apart.
The patchy-looking males on the left are moulting out of their breeding finery, into eclipse plumage. This takes place in autumn, and these photos were taken in February when moulting was already underway.
"Australian malurids have a complete moult, which starts after the breeding season, often in January, and is complete by April or May in southern Australia. For the lesser-known northern species, the timing appears to be similar. In southern Australia, the mass of contour plumage, and therefore plumage insulation, of Superb Fairy-wrens is greater in winter than in summer. Although the tail feathers are moulted at this time, they may be lost and replaced at any time of the year; the primary moult is descendant." (Lynx Ed)
But not all males moult into eclipse plumage. Dominant males may retain their breeding plumage all year round. More from Lynx Ed:
"Some adults acquire little or no non-breeding Dull body plumage, appearing instead to moult directly from one Bright body plumage to another. In studies of Superb Fairy-wrens carried out in Canberra, R. A. Mulder and M. J. L. Magrath found that only five of 426 males, fewer than 1%, did this; all five were more than four years old, but not all males older than four years moulted in this way each year."
Since it is the young female wrens that disperse from the group while the males stay at home until their own, or a neighbouring territory becomes vacant, groups usually contain more males than females. This is more pronounced with superb fairy wrens than variegated wrens, which may contain more female helpers. Some of the offspring, especially males may stay in the home territory for years, so groups of these two species sometimes contain several brightly coloured males.
"In the case of the Superb Fairy-wren in Canberra, in south-east Australia, all young females disperse in their first year, in two distinct phases. Some females leave early, mostly 1–2 months after they fledge, and their dispersal is not in response to any obvious aggressive behaviour by the group; these females are most likely to be some of those hatched early in the breeding season. The second phase of dispersal takes place shortly before the next breeding season, and occurs in response to persistent maternal aggression." (Lynx Ed)
With red-backed wrens, the story is a bit different.
Jordan Karubian, who studied red-backed fairy wrens for his PhD says that only one quarter of males moulted into bright plumage for the first breeding season, but most did so in their second season. He found that although plumage colour was set once moulting had occurred, bills could darken quite rapidly if the bird's status was elevated from non-breeding to breeding, such as with the death of the dominant bird.
Thus, it is possible with this species to find breeding occurring between two brown birds, a male and a female, without any male in brightly coloured plumage.
Part 3 looks at some of the photos of wrens at Koreelah to try to determine the species of wren, and the relationship to the group.
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Wikipedia
https://en.wikipedia.org/wiki/Superb_fairywren
Gaia Guide
http://www.gaiaguide.info/Group.html?groupId=xOGkh57c
Lynx Edicions
http://www.lynxeds.com/family-text/hbw-12-family-text-maluridae-fairy-wrens
Karubian
http://www.environment.ucla.edu/ctr/staff/karubian/Karubian-J-Avian-Biol-2008-1.pdf
