Olive-backed Orioles

First-year immature Olive-backed Oriole

I was banding birds at Charcoal Tank Nature Reserve again last weekend, with Mark Clayton, Harvey Perkins, Peter Ewin, and others. It is now late autumn and aging some of the birds is becoming difficult as they lose their juvenile and immature plumages ready to moult into full adult breeding plumage, before the next breeding season begins in a few months. Further species will be highlighted in later posts, but for now I have posted some images of two Olive-backed Orioles Oriolus sagittatus which we caught. One was a first-year immature bird and the other a second-year immature bird, which was particularly difficult to ascertain an accurate age for, as so many plumage features are comparative. Hopefully these images will help others to discern the ages of Olive-backed Orioles in future.

Second-year immature Olive-backed Oriole

The presence of buff-tipped wing coverts is always a good feature to look for in young birds and the first-year oriole had obvious buff tips on all its greater and median coverts.

Very obvious buff tips to the coverts - 1st yr

The second-year bird only had a few buff-tipped greater coverts, which were not obvious even when the bird was held in the hand. The second-year bird's primary, secondary and tail feathers were also darker than those of the first-year bird, similar to those of an adult.

Only a few buff-tipped greater coverts - 2nd yr

Adult Olive-backed Orioles have grey wing coverts with dark centres, and no buff tips. The image below is of an adult female's wing, from a photograph of a bird caught in a previous breeding season, when it was confidently aged as a breeding adult bird.

Adult wing coverts with no buff tips

The facial markings were also good for determining the birds' ages. The first-year bird had an obvious cream-buff supercilium, a dark eye and bill.

Obvious supercilium and dark bill - 1st yr

The second-year bird had a faint supercilium, red eye and a brownish bill with a pink flush. The streaking on its chin and throat are very similar to those of an adult female, and a second-year bird cannot be sexed until its plumage shows either a heavily streaked chin/throat or not, once its bill has become bright red.

Faint supercilium and brown bill with a pink flush - 2nd yr

The last two images are of adult Olive-backed Orioles caught in a previous breeding season at Moruya while banding with Anthony Overs. Neither bird has a noticeable supercilium, their irides are red and their bills are bright pink.

Adult female Olive-backed Oriole

Adult females have a streaked chin and throat, while the males have more of a green hood extending down around their throat. The females also have heavy streaking on their backs while the males only have light streaks.

Adult male Olive-backed Oriole

Lord Howe Island birds

Two Lord Howe Island Pied Currawongs on the summit of Mt Gower

Oceanic islands, far from large landmasses, often have a suite of unique fauna, and as Lord Howe Island is quite isolated, it has such a list. Unfortunately, as with many islands, some of the native species have been lost, a euphemism for having been eaten to extinction by man or animals introduced by man. Nevertheless, it still has the character of a wild island, especially up on Mount Gower (see previous post) and here are a few birds which added to my recent experience there.

The local subspecies of Pied Currawong has a longer, narrower bill than the nominate race.

As we climbed up through the forest to the plateau, loud chuckles and coughs followed us from the thick canopy. These were the calls of the local Pied Currawongs Strepera graculina crissalis, which have a distinct island accent, and they seemed to be telling one another of our approach.

A little more secretive, but never timid, and quite happy to forage around our feet as we passed, were the Woodhens Gallirallus sylvestris, This flightless species was saved from extinction, by the collection of a group of birds which had escaped predation on the almost inaccessible summit plateau, screened off from pigs etc by cliffs. The birds bred successfully in captivity and now that birds are running wild in the lower forest as well as the plateau, the future looks bright for the species.

 Lord Howe Island Woodhens forage for food in the rich basalt and leaf-litter soils 

Meanwhile all around, there is the incessant calling of Providence Petrels Pterodroma solandri in the sky.

Providence Petrels wheel around the Mt Gower cliffs

Ocean, cliffs, high hilltop, mist forest and flocks of petrels - a wonderful experience

There aren't many viewpoints out from the plateau as the forest is so dense, but looking out over the ocean from so high added an extra quality to the scene. Then our guide, Dean, called some petrels down. All he did was give a few yodels and in they came, crashing through the canopy and onto the ground.

Some petrels landed clumsily on branches

Others crashed to the ground and immediately started to squabble

They had no fear of us whatsoever

Unfortunately for the species, due to their disregard for humans, Providence petrels were eaten to extinction on neighbouring Norfolk Island. They were so easy to kill. There were more people on that island than Lord Howe, as there still is today, and it is probably lucky for the birds that Lord Howe has never been highly populated by man. Although who knows what hidden anthropogenic dangers might still wipe them out - they eat plastic debris in mistake for food, it accumulates and fills their stomachs, eventually causing death by starvation. Let's hope this doesn't lead to another extinction.

To see a clip of David Attenborough calling down Providence Petrels on Lord Howe Island click here

Mist Forest

Mount Gower (on the right) is often kissed by cloud on even bright sunny days

On a recent trip to Lord Howe Island, I went up onto the summit plateau of Mount Gower to see the lush growth of plants there - mist forest plants, growing on a sub-tropical island far out in the ocean.

The cloud which gathers on the summits of Mounts Lidgbird and Gower
 adds height to the perspective when seen from the fields

The twin peaks of Mounts Lidgbird and Gower stand tall over the rest of Lord Howe Island and to me, with my sense of exploration, I just had to go up there, to Mt Gower, the higher of the two at 875m.

The mist brings water to what might otherwise be a very dry place

There is no easy way up there, as the rise is so steep and cliffs block most lines of approach.

The first part of the climb follows the path across this cliff at mid-height,
then around the corner and up a steep valley to the final tower

On the plateau, the vegetation is short, wind-clipped as on most mountains, but still several metres high. Although oceanic, it is so high that there is very little salt in the atmosphere. The whole gives the effect of a ground covering of ferns and shrubs, linked to a low canopy by a tangle of moss-draped branches.

The rich vegetation crowds over the faint path

Overall, the colour is green vivid, leafy green - with the calming effect of a studio green room. And it is dark under the lush spread of palm and fern fronds - difficult conditions for photography.

It is a true jungle up there

Showy plants like the orchids catch most people's attention, but once seen there are other botanical treasures.

Bush Orchid Dendrobium macropus howeanum

Little Mountain Palm Lepdorrhachis mooreana
one of several endemic species only found on the top of these island mountains.

It is the abundance of lush growth that is the overall impression, especially that of the mosses which swarm over branches, stumps and rocks. It is their presence that tells this is a true mist forest, for they could not live without the frequent covering of cloud on those ocean mountain tops. 

Moss in so many forms like this feathery species

A moss blanket spread over a boulder

And a meandering trail of moss climbing over all on its way

New paper on Tawny Frogmouth nesting behaviour

The cover of the current edition of Australian Journal of Zoology is illustrated with one of my photographs,
showing a Tawny Frogmouth in a typical nest site

The current issue of the Australian Journal of Zoology carries a paper by me and Duncan Rae on the nesting behaviour of Tawny Frogmouths in the Canberra area. This presents and discusses a set of results based on 253 nest records over several years. The brief online abstract and citation are reproduced below, but the full abstract and paper can be obtained by clicking on this link: Orientation of tawny frogmouth (Podargus strigoides) nests and their position on branches optimises thermoregulation and cryptic concealment

Tawny frogmouths (Podargus strigoides) in south-east Australia place their nests on open coarse-barked branches orientated to the north-east. This would fit their cryptic plumage and behaviour, expose the nesting birds to sunshine, shelter them from prevailing wind, give good visibility for detecting predators and clear space for rapid escape.

Rae, Stuart and Rae, Duncan (2014). Orientation of tawny frogmouth (Podargus strigoides) nests and their position on branches optimises thermoregulation and cryptic concealment. Australian Journal of Zoology 61, 469-474.

A Tawny Frogmouth sits over his two chicks

Striated Pardalotes - juveniles

A juvenile Striated Pardalote - nominate Pardalotus striatus striatus

When we caught two young Striated Pardalotes Pardalotus striatus on the last trip to Charcoal Tank (see previous posts), I noticed that they were of different subspecies. The one above is of the nominate type striatus, which only breeds in Tasmania and spends autumn and winter on mainland Australia, where it overlaps the range of two subspecies, ornatus and substriatus. The nominate has yellow wing-spots, colouring on the tips of the greater primary coverts, while the subspecies have red wing-spots - see below.

The yellow wing-spot on the primary coverts of a  Pardalotus striatus striatus

The red wing-spot  on the primary coverts of a Pardalotus striatus substriatus
(The wide band of white on primaries differentiates this subspecies from the similar subspecies ornatus, which has narrow white edges to the primaries. See post of  17th September 2012)

A juvenile Pardalotus striatus substriatus

Then I noticed that the striatus juvenile's moult into adult type plumage was less advanced than that of the substriatus bird. In particular, its crown was still spotted rather than streaked like that of the substriatus (see below). This is only a sample of one from each subspecies, but I wonder whether the young Tasmanian striatus birds deliberately delay their moult until they have migrated across the Bass strait and settled in their winter range on the mainland. Meanwhile the resident subspecies of South-west New South wales, substriatus, begin their moult as soon as possible. Both birds were caught on the 15th March 2014. If the Tasmanian birds migrate from March-April (HANZAB), this bird would have been one of the earlier to leave. Would it have been one of the earlier to hatch too? If so the delay in its moult would be more likely a strategy to moult post migration. I would be grateful if anyone has more information on the plumages or migration strategy of juvenile Tasmanian Pardalotus striatus striatus.

Juvenile Pardalotus striatus striatus,
with a spotted crown

Juvenile Pardalotus striatus substriatus,
with a partially streaked crown