Tuesday, 23 May 2017

Comb-crested Jacana

The Byron Bay Integrated Management Reserve is a great place to see both terrestrial and water birds in the Byron Bay area. As access to the wastewater treatment wetlands is limited, it is one of the few places in the area accessible to birders that is not heavily impacted by human presence and activity.

Comb-crested Jacanas (Irediparra gallinacean) are common at the wetlands, especially on Cell H which has a large covering of water lilies. The local population when I visited included adults, sub-adults and juveniles, indicating successful breeding at the site over last summer’s breeding season.

The Jacana’s bright red comb or wattle, for which the bird is named, is conspicuous on the adults. The combs are large and bright red on mature adults, smaller and a dull flesh colour on sub-adults and almost non-existent on the juveniles.

It seems adult birds can change the colour of their combs. HANZAB states that colours can change rapidly, from yellow through to red, but ‘Causes of colour change are not properly known but to some extent are behavioural; yellow combs flush to red during or after territorial displays or fights. Yellow combs are often recorded on males incubating eggs.’ 

I observed adult birds for a while that seemed to have continuously red combs!

During the breeding season, males maintain their own territories, and females may range across territories of several males with which they mate.  The male does all the incubation but females may also contribute to care of chicks.  

HANZAB indicates that the sexes are only separable by size, not plumage or comb.  

There is no suggestion in HANZAB that flushing of the comb is associated with courtship rituals. It may be that flushing of the comb has more to do with maintaining feeding and nesting territories than mate selection per se.

Jacanas were observed and photographed from the bird hide on Cell H. The birds foraged alone and ranged far and wide across the pond so I had to sit patiently and wait for birds to come within range.

Please click on photos to enlarge.

Cell H with bird hide.
Juvenile Jacana – note there is very little comb development, head is rufous not black, no black breast bar or black tip to bill.

The young Jacanas even at hatching have large feet so they can be mobile on floating aquatic vegetation immediately.
This is a sub-adult bird – note the comb is not well developed and is a dull pink colour, the bill is brown with no black tip, however a black breast bar is developing and the crown feathers are turning black.
Another sub-adult bird.

Adult bird with fully developed red comb. 
Cropped version of the photo above showing the comb is translucent in the late afternoon light. 
The comb is red-orange on this adult bird.
A cropped version of the photo above shows blood vessels in the fleshy comb. 

The Jacanas were very active, constantly on the move, foraging across the lily leaves or moving through rushes so most photos had to be taken of the birds while they were moving.

This bird however paused and it soon became apparent it was settling down for a rest.

As with many birds it rested on one leg which involved tucking its very long feet up under its wing.

The tips of the three front toes are just protruding from the wing however the rear toe is mostly exposed.

In this photo the bird is looking sleepy!

All birds have evolved characteristics to exploit ecological niches with some able to generalise while others, such as Jacanas, are highly specialised. I find the development of extraordinarily large feet to enable exploitation of the floating world of aquatic plants particularly fascinating.

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