Monday, 18 April 2016

Spotted Bowerbirds

Conflicting aging criteria?

While studying birds at Bowra Wildlife Sanctuary recently, Mark Clayton and I caught these two Spotted Bowerbirds Chlamydiae maculata and as we were not familiar with the plumages of the different ages and sexes, I photographed them. Now upon closer inspection I find myself confused by the literature and give my interpretation of their age and sex below.

An adult or young bird

An obvious feature of this Spotted Bowerbird's plumage - to a bird ringer/bander - are the bars through the pale rufous tips of the secondary coverts. According to the text of the plumage guide to aging these birds in the Handbook of Australian, New Zealand & Antarctic Birds, HANZAB, this feature identifies the bird as an adult. However, the other features of the bird's plumage indicate that it is a young sub-adult bird. Also, online images of apparent adult birds at bowers show birds with large nuchal crests, and there are no bars through the tips of their secondary coverts e.g. While those of apparent young birds, by their generally pale plumage and lack of crest (HANZAB), show birds with bars through the tips of these feathers.

The second bird shown below seems to be an adult as it has a large pink nuchal crest, a red iris and richly contrasting plumage of dark, almost black and rufous feathers (HANZAB).

This image illustrates the first bird's head, showing the small nuchal crest
 of pink feathers and a slate-grey back to the neck.

This image of the second bird shows a larger, adult-type nuchal crest
 and a similar grey back to the neck

The first bird has only a few pink feathers in its crest,
and the crown feathers are dull rufous/brown with faint dark edges

The second bird has a thick group of pink feathers in its crest,
 the crown feathers have a contrasting dark edges,
those in the fore have white tips.

I suggest that the first bird is more than one year old and not older than two, a sub-adult, 2- in the Australian aging category system. The feathers are generally of low contrast in tone and many of the coverts have pale tips. It is possibly a young male as the slate-grey feathers on the back of the neck are similar to those on the second bird, which by the same criterion seems to be a male. Females have white streaks through these feathers (HANZAB).

The second bird has a rich contrasting dark brown/rufous plumage and obvious pink nuchal crest feathers. I suggest that this bird is an adult male (2+) as it does not have any white streaks through the grey patch at the back of the neck.The bird was also beginning to moult its primary and tail feathers, which is typical of adult birds post-breeding, the period when we caught the birds, in March.

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