Friday, 28 March 2014

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


Tuesday, 25 March 2014

Australian Emperor Dragonfly

While out at Charcoal Tank Nature Reserve, by West Wyalong, NSW last weekend, where we were catching birds as mentioned in the previous post, Tony Stokes found and pointed out a dragonfly which was perched on the trunk of a Red Ironbark while the sky was overcast and dull.

This was an adult male, identifiable as such by the pair of claspers on the end of the abdomen.
It was an Australian Emperor Dragonfly Hemianax papuensis, which is common and widespread throughout Australia, New Zealand, New Guinea and neighbouring islands. It is a large insect, about 7 cm long, with a predominantly yellow head, thorax and abdomen, striped with contrasting brown or black. The choice of a dark-barked tree for a roosting site showed off the yellow well, especially on the leading edges of its wings. While the dull sky and cool air kept it motionless, giving a chance to see the detail of the insect's intricate wing-vein structure.

Seen from an angle, the insect's aerodynamic form is perfect 

Monday, 24 March 2014

Young birds - how to determine their age

A young Striated Pardalote, less than one year old
On the last trip to study birds at Charcoal Tank Nature Reserve, NSW, over the weekend of 15-16th March, which was run by Mark Clayton as usual, we caught a variety of young birds. This was not surprising as it was only a month or so after the main breeding period for most birds in the area had ended, but we caught 26 species amongst the 119 birds caught altogether, and determining the age of birds can be tricky. So to help illustrate just how these young birds were identified, I have set out below some examples of the various methods that can be used to establish their age.

A front-on view of the same young pardalote
Immature Plumage -  The main, quickly seen features which were followed to determine this Striated Pardalote Pardalotus striatus as a young bird were the beginnings of only a few streaks on the crown and no white eyebrow behind the yellow flash above the eye. This bird will gradually moult out its first young-bird feathers and grow true adult-coloured feathers during its first year of life, with a fully streaked crwon and a wide white eyebrow.

A young Double-barred Finch
Feather development - To the trained eye, this Double-barred Finch Taeniopygia bichenovii is likely a young bird as it has narrower black bands across its breast than an adult would have. But that is a relative criterion, which is not of much use if there is not an adult to compare it with. More precisely, it can be aged as a young bird, less than one year old, by the incomplete covering of underwing feathers. In the second image, the flesh and line of the bones can be clearly seen because they are not fully covered like those in an adult bird. The most important feathers for a young  bird to grow are its body feathers for warmth, then flight feathers for mobility. The sooner they can leave the nest, the easier it is for them to escape from predators. So they gradually complete their body plumage in the less exposed parts, such as under their wings, as they continue to develop into full-grown birds. 

The partially bare underwing of the same young Double-barred Finch

A young White-plumed Honeyeater - in its first year
Pigmentation - this can be costly for a young bird to lay down, nothing comes without cost, even in nature. So young White-plumed Honeyeaters Lichenostomus penicillatus concentrate their nutritional resources in growing a basic bill, enough to serve the purpose of feeding, preening etc.. There is no need for deep pigmentation. That is added slowly during its first year of life, and by the following breeding season it will have a fully black shiny bill, a sign of an adult bird in breeding plumage.

This first-year White-plumed Honeyeater is probably a few months old and has begun to grow a dark bill,
 starting from the tip

Young Sacred Kingfisher - less than one year old
Buff-tips - many young birds have buff-tips to some of their feathers, such as this young Sacred Kingfisher Todiramphus sanctus, which has such feathers in its wing coverts and crown. Most of these will be moulted out during the first year, and the bird will be in adult breeding plumage in time for the next season. Some other species can retain a small number of these buff-tipped feathers into their second year while they are breeding, but if a Sacred Kingfisher has lots of such feathers between breeding seasons, then it can be confidently classified as a first-year bird. 

A back-view of the same kingfisher - this bird has a broken tail feather, snapped along the line of a fault-bar. This is a weak part of the bird's tail feather which is a result of less keratin being laid down in the feather during a period of less nutrition intake as the young bird's tail grew

A young rainbow Bee-eater
Ornamental feathers - or lack of.  Some species of birds grow elaborate ornamental feathers as part of their adult breeding plumage, like the Rainbow Bee-eater Merops ornatus which have extended central tail-feather streamers. The young birds however, do not grow these. To grow such feathers for no purpose in their first year, as they are only required for breeding display, would be an excessive waste of nutrition. 

Thursday, 13 March 2014

Gang-gang Cockatoo Survey

An adult male gang-gang inspects a potential nest hollow
Today saw the launch of the Canberra Ornithologists Group's Gang-gang Cockatoo survey. The survey organiser, Chris Davey introduced the project to a group of birders at Corroboree Park, then naturalist Ian Fraser added a few details and anecdotes to inspire people to go out, find the birds and log their results in the online survey - All records of Gang-gangs in the ACT and surrounding district are welcome, including negative ones, and there are already hundreds entered. The project runs for eighteen months to cover all seasons fully and we hope to have a clearer picture of where the birds breed, overwinter, and what habitats need to be preserved if the birds are to be here in the future. So if any one in the area can add information to the survey please do, it's easy, and rewarding. 

I was involved in the design and production of the survey brochure, a fold-out introduction to the bird and project. See below.

Sunday, 9 March 2014

Huge deposits of pumice on the beaches

Piles of pebbles of pumice lie on the tide-line along the new South wales south coast
The sandy beaches and hidden coves of the New South Wales south coast are presently littered with pumice pebbles. They have come from 4000 km out in the Pacific Ocean, north of New Zealand, where a submarine volcano on the Havre Seamount, near the Kermadec Islands erupted last July. This caused a raft of pumice covering 20,000 sq km to form and gradually drift west on the currents. When they reached the Australian coast they were washed up and concentrated on the tide-line. 

The pumice formed as lava erupted under water and air trapped in tiny pockets in the rock makes the it buoyant. This was the largest such eruption in the region for over fifty years. There were all sorts of plant and animal life attached to some of the larger and rougher pieces, and I wonder what land-based life will find a niche in the new rocky tide-line. 

The pumice is light and floats like the bladders of the seaweeds which it lies with on the shore

Most of the pebbles are small, but some are as large or larger than a cricket ball

The pumice floated from north of new Zealand to the south east coast of Australia