Monday, 23 December 2013

White-winged Choughs – expanding red eyes.

White-winged Choughs (Chough is pronounced chuff) are birds of dry open eucalypt forests and woodlands. Highly social birds with fascinating group behavior they spend much of the day fossicking in ground litter for food. At this time of year the young are out of their large mud bowl nests, following the adult birds of their extended family group about, begging incessantly to be fed.
The white patches on their wings are only visible when the wing is opened in flight or when displaying or grooming.
An adult White-winged Chough - note white wing panels in flight feathers.
Adult choughs have a red eyes, the iris is orange, while young birds have a brown iris.
Adult bird excavating hole in soil under ground litter to uncover insect larvae. Note the red eye.
This is a juvenile White-winged Chough note white eyebrow. The iris is brown however a small section of the eye ball visible in this photo shows the eye ball surrounding the iris is pink as in adult birds.
The choughs on our property are used to humans and are quite confiding, allowing close approach for observation and photos.
I have noticed in the past that the red eye of adults sometimes appears larger than normal and until now had not given it much thought or looked closely to see how this is achieved. Choughs are highly excitable birds sometimes responding to disturbances within or external to the group by spreading their wings, fanning their tail and also by enlarging their red eyes.
This is the adult bird feeding in photo above. It has moved on and found an insect and suddenly become excited by my presence. The red eyes have been enlarged, wings and body feathers spread and tail fanned. The display is meant to look threatening.
The following two enlarged shots show first a calm bird feeding with normal eye appearance and then an excited bird with an enlarged red eye.
Enlarged photo of adult bird from feeding shot above showing close up of head and the normal elliptical eyelid position of a calm bird.
A close up of the excited bird displaying in photo above. The wing, body and tail feathers have been contracted however the eye lids remain expanded showing an enlarged eye with an orange iris and pink surrounding eye ball. Its display has distracted it from eating the small beetle it caught before becoming alarmed by my presence. 
One field guide states that the outer eye ring flushes brighter red giving the impression that there is a colour change to the eye. The above photos show that rather than the eye changing colour, the bird achieves an enlarged red eye by uncovering the eye by expanding the surrounding eyelid. The eyelid is normally held in an elliptical shape and is opened out to a circular shape when the bird becomes excited. 
The field guides describe a red eye and from a distance the eye does appear to be red however on closer examination the iris is orange and the surrounding eye ball is pink.
If you have ever wondered about the Chough’s expanding red eye, now you know how it is achieved. For those readers who already knew this I hope you enjoy the photos.

Sunday, 22 December 2013

Nest theft, recycling or deliberate destruction?

This morning I was checking out birds in a mature woodland on our property. The grassy woodland is dominated by Gippsland Grey Box with other species mixed in such as Forest Redgum, Red Stingybark and Red Box. There were lots of very vocal birds present including Dusky Woodswallows, White-winged Trillers, Jacky Winters, White-throated Gerygones, Bell Miners, Rufous Whistlers, Grey Shrike-thrushes, Grey Butcherbirds, White-winged Choughs, Grey Faintails, Willie Wagtails, Yellow-rumped Thornbills, Spotted Pardalotes and a number of Honeyeater species ……. and a koala tried to sleep through the din.
Suspended from the slender stems of a Red Box about 2 metres above the ground, I came across a nest. The nest was fresh and intact and looked to be the type constructed by a number of honeyeater species, a deep suspended cup made from bark and fine grass fibres bound together with cobwebs.  As I approached for a closer look, a White-naped Honeyeater approached the nest and inserted its head into the cup and then withdrew and flew off. I thought, great, I have found an active nest and one of the adult birds has just made a visit to feed young.
The intact Honeyeater nest photographed just after the White-naped Honeyeater left.
A White-naped Honeyeater - this one was photographed at Mallacoota.
Hoping the White-naped Honeyeaters would return and provide some photo opportunities I moved to the cover of a low leafy side branch of a nearby tree with a good view of the nest and good sunlight angle and waited.
Shortly a Honeyeater approached the nest. Before I could consider if this was the owner of the nest, perhaps the White-naped Honeyeater seen at the nest a few minutes earlier, this bird commenced to rip material from the nest and to my surprise I realized it was a Brown-headed Honeyeater. It worked with haste – as you would expect from a guilty thief anxious not to be caught. The bird took material from one of the two sections that suspended the nest from the tree stem, causing the nest to swing open. The nest then remained suspended by two tenuous connections on one side of the nest. The bird soon departed with a bill full of bark fibres.
A Brown-headed Honeyeater has arrived at the nest and removed material causing the nest to tilt and open.
The bird then worked its way around the nest - for what purpose I do not know?
The bird then took some nest material in its bill and departed.
With no action for five minutes or so I departed the scene for lunch and returned later to see if any more material had been removed from the nest, see if the birds were still active and see if I could find the new Brown-headed Honeyeater nest.
The state of the nest when I departed for lunch at noon.
The state of the nest when I returned an hour or so later - it is now hanging precariously from two slender threads.
On my return, as luck would have it, I did not have to wait long for some action. This time two Brown-headed Honeyeaters approached the nest. Apparently both male and female share the nest building work and also in this case the presumed theft of nesting materials.
The first bird at the nest soon ripped some material off and departed. The nest was now only attached to the stem by two very frail looking strings of fibre.
Two Brown-headed Honeyeaters returned shortly after I commenced watching the nest again. The first bird took some material and left.
When the second bird jumped onto the nest the first string of fibres broke, followed closely by the second and the nest fell to the ground.
The second bird jumped onto the nest - one slender thread broke, then the second and the nest fell to the ground.
I was too slow to capture a shot of the second bird when it flew down and ripped some material from the nest and departed.
The second bird flew down and removed some material from the nest on the ground. Fortunately I noted the bee-line direction both birds took as they departed the scene so I then headed in that direction to see if I could find the new nest.
There was still some nest material wrapped around the stems and both birds made a couple of trips to gather this. I did not see them go to the nest on the ground again.
While looking for the new nest, both birds flew close past me on one of their return trips with a White-naped Honeyeater in hot pursuit. The White-naped peeled off and I watched the birds fly up into a dense canopy of eucalypt leaves where I spotted the well concealed nest. The new nest was about 80 metres from the ransacked nest and much higher, about 10 metres above the ground.

The Brown-headed Honeyeater nest well concealed in the dense canopy of a young Grey Box.
It is hard to be sure whether the ransacked nest belonged to the White-naped Honeyeater. However I did see it earlier at the intact nest and again later, chasing the two Brown-headed Honeyeaters returning to the nest they were constructing with material from the ransacked nest. Based on this it seems reasonable to assume that the nest did belong to the White-naped Honeyeater. The nest certainly conformed to the type of nest this species builds.
So I think this was a case of deliberate theft rather than recycling.
Materials from old or abandoned nests are sometimes recycled either by their owners or by other species. In this case the nest did appear to be a fresh, recently completed nest. The downy feather lining looked to be very fresh and unused. I would have to say that the location of the nest, more or less in the open, left it very vulnerable to attack by predators.  So if it had been used there would have been a high chance of it being plundered, either for eggs or young, by birds such as Currawongs, Butcherbirds or Kookaburras.
Construction of the Brown-headed Honeyeater nest looked to be well advanced and certainly could not have been constructed to the stage I found it in with materials only from the White-naped Honeyeater’s nest.
So it would appear that the two Brown-headed Honeyeaters have destroyed the nest of another species for the sake of a small quantity of material they have used to put the finishing touches to their own nest.
Interesting behavior, not easy to explain?
If they were interested in obtaining a maximum amount of material from the nest while it remained suspended above the ground, minimizing the risk from predators, then removing fibres critical to the attachment and suspension of the nest is not a good approach.
Perhaps the Brown-headed Honeyeaters saw the proximity of nest of a closely related Honeyeater as a threat or competition and this may explain why they destroyed the nest for such a small quantity of material.  Their approach to removing material from the nest was certainly the quickest way to destroy it.
Whatever the case, it seems I happened to stumble upon the intact nest just as the Brown-headed Honeyeaters made their first visit either to steal materials, with destruction of the nest an unintended consequence of their action, or to steal material with the deliberate intention of destroying the nest?
I don’t think recycling of material from an abandoned nest applied in this case.
The progress of evolution is marked by such daily dramas – the lesson from today for the White-naped Honeyeater would be to build the next nest in a less obvious location.

Post script:

Received the following email response from a friend with comments and references to nest material theft among honeyeaters which you may find of interest:

Hi Avithera,  Cannot recall the species but I've seen this over the years as well.

A web search picked up mentions of this.  See this blog for example ...

And at least one paper in the Journal Corella ...
LEY, A.J., D.L. OLIVER & M.B. WILLIAMS. (1997). Theft of nesting material involving Honeyeaters (Meliphagidae). Corella21: 119--123.
Thieving of nesting material in 10 honeyeater species and six other passerines is described, in the Bundarra-Barraba region west of Armidale, New South Wales during a study of Regent Honeyeater's biology in 1995-96. Theft of nesting material was from both active and inactive nests. The contribution of theft to nest parasite transfer (e.g. lice) and to nest failure in Meliphagidae is discussed.

Reckon that HANZAB would have mention as well under the relevant species accounts ...

Have a good day!