Wednesday, 21 June 2017

Red-kneed Dotterels

The beautifully coloured Red-kneed Dotterel (Erythrogonys cinctus) is confined to mainland Australia and southern new Guinea with vagrant records in Tasmania and NZ. A nomadic shorebird, found mostly in freshwater habitats, they turn up on the Gippsland Lakes wetlands on a frequent but irregular basis.

They are a very distinctive shorebird – I like the apt description in the Pizzey & Knight Field Guide “black hangman’s hood” – and are unlikely to be confused with any other shorebird seen in Australia.

Recently I found about eight Red-kneed Dotterels feeding in mirror still shallow water at the sand islands in Jones Bay (on the Gippsland Lakes south of Bairnsdale). With the sun low in a late June clear blue winter sky and Jones Bay behind me reflecting and amplifying the light, the Dotterels were bathed in an abundance of red-end-of-the-spectrum light giving a saturated look to the colour of some of my photos. Amongst several birds in the photos some show black hoods and breast bars and others look brown. I am not sure if this is due to the light angle or if there is a real colour difference due to maturity of the birds?

Please click on photos to enlarge.

This is the location of the photos – the Red-kneed Dotterels were feeding in shallow water just off the sandy shoreline near the middle of the photo.















The birds were actively feeding by probing for food in the sand.
The knee (actually an ankle) is red and the rest of the leg (tarsus) is grey.
This photo was included to show the colour difference between some of the birds, some very black and others brown.







The red tibia and knee and grey tarsus show well in the this photo.

 
A close portrait to finish.





Sunday, 18 June 2017

White-faced Herons

For several years now we have had a resident pair of White-faced Herons (Egretta novaehollandiae (1)) and each year they nest in a large Forest Redgum (E tereticornis) on our property. The breeding season in SE Australia is normally from September to December and while it is only mid-June now, the pair are both in breeding plumage and are keeping close together as they feed in our paddocks. They are preparing to breed.

The breeding plumage consists of long lanceolate nuptial plumes which are silvery grey on the mantle and scapulars and chestnut on the breast.

Please click on photos to enlarge.

Adult White-faced Heron in breeding plumage.

One bird is slightly, though noticeably, larger than the other. In the field guides which I have consulted there is no mention of a size difference between the sexes and as the sexes look similar I am unable to say which sex the larger bird is.

I waited a long time hoping to get a side by side comparison photo of the pair who mostly foraged apart.

This is the best I could achieve – the bird in shadow at the rear is the larger bird. 

Herons, including the White-faced, have several highly modified patches of feathers that produce powder-down - a talcum-like powder that is used for grooming and cleaning feathers. Some other species of water birds have powder-down patches as do some non-water bird species such as wood-swallows for example. The powder gives the plumage a powdery appearance and reduces the fine feather detail giving a slightly blurry appearance. I first noticed this with some woodswallow photos that I thought were out of focus until I learnt about powder-down.

The White-faced Heron is easily our most well-known heron being both abundant and widespread and can be found from coastal habitats to far inland, wherever there is water. The pair on our property have access to a small farm dam and the Nicholson River nearby, and suitable trees to nest in, however they spend a lot of their time foraging for food on grassy paddocks rather than in shallow water.

White-faced Herons are “habitat generalists” and can be found hunting fish in water or worms in a paddock as they have been doing at home over the past week or two. Pretty much any vertebrate or invertebrate animals they come across that are small enough to swallow are potential food for White-faced Herons.

I have been coming and going on the tractor through their favoured feeding paddock recently and when I do they usually fly to a nearby fence post and when I have passed by they return to the paddock to forage.

One of our resident White-faced Herons perched on a fence post waiting for me to depart the paddock so it can return to foraging.

Compared with some egrets and herons that have adopted the “stand-and-wait” approach White-faced Herons are more active hunters. The hunting technique used in our paddock is “stealthy stalking” and when a food item has been spotted the long and sharp dagger-bill is thrust out at lightning-speed to catch the item in a pincer grip. The sharp bill can also be used to spear larger prey such as fish.  

All herons have a special hinge mechanism at the sixth vertebra which facilitates the lightning fast, forward thrusting movement of the neck, head and dagger bill when seizing or impaling prey.

With the camera supported on the top of a fence post I watched the pair stalking through the relatively short but thick grass searching for earthworms. Their eye sight, and perhaps hearing, must be exceptionally good to spot earthworms on or partially under the ground in dense grass. Once a worm was spotted and their gaze was fixed on the hapless prey, the lightning fast strike almost always resulted in a worm capture. The worm was swallowed so quickly I only managed to capture a couple of photos showing the worms in the bill.

Evidence of the food they are taking from the paddock - earthworms.

Another worm captured in a precise pincer grip with the very tip of the bill.

The following photos are a selection from about 80 I took of the pair stalking earthworms in the paddock.

At any sign of a potential threat, for example a magpie’s alarm call, foraging is interrupted and the heron’s head goes up like a periscope to check for danger.

Lunging into the grass – the grass is not quite as thick as it appears in this foreshortened view through the camera lens.

I can’t recall if this was a rare miss or the bird has just swallowed the worm?

The hunt continues.

The long neck allows for a forward look beyond any disturbance caused by the feet.

The forward-facing eyes are essential for good vision to locate prey and for accurate control of the bill strike.  
When hunting, the herons have a look of complete focus and concentration.

The foot is poised; the eye is focused. 

Herons and the closely related egrets are beautiful and elegant birds – we are very fortunate to have a resident breeding pair of White-faced Heron virtually in our backyard.  


(1)  Note regarding the name herons and taxonomy.

The scientific name for the White-faced Heron (Egretta novaehollandiae) shows it is in the genus Egretta and therefore is an egret and not a heron?

The names heron and egret have no taxonomic relevance with the vernacular name egret being used for white birds and heron for the non-whites. A look at a copy of the taxonomic list from Christidis and Boles 2008 below shows the Eastern Great, Intermediate and Cattle Egrets in the heron genus Ardea and Pied and White-faced Herons in the genus Egretta.

I guess Bitterns, Egrets, Night Herons and Herons can all be regarded as herons, or should that be egrets?

Copied from Christidis and Boles 2008

CICONIIFORMES

Ardeidae
Australasian Bittern
Botaurus poiciloptilus
Australian Little Bittern
Ixobrychus dubius
Black Bittern
Ixobrychus flavicollis
White-necked Heron
Ardea pacifica
Eastern Great Egret
Ardea modesta
Intermediate Egret
Ardea intermedia
Great-billed Heron
Ardea sumatrana
Cattle Egret
Ardea ibis
Striated Heron
Butorides striata
Pied Heron
Egretta picata
White-faced Heron
Egretta novaehollandiae
Little Egret
Egretta garzetta
Eastern Reef Egret
Egretta sacra
Nankeen Night-Heron
Nycticorax caledonicus