Friday, 24 January 2014

Feathers make the bird - a look at juvenile, immature and breeding feathers

If clothes make the man as the old saying goes, then feathers certainly make the bird!
Feathers have developed for insulation and flight however evolution of extravagant male breeding plumage is probably the main reason why we find birds so attractive? This is a male Variegated Fairy-wren in very obvious and spectacular breeding plumage.
It is easy to take for granted the amazing structure and function of feathers and their incredible diversity, which has enabled birds to inhabit every part of the globe from the tropics to the Polar Regions and from the skies to the oceans.
This post briefly considers the basic stages of feather development from chicks to adult birds.
The various plumage types or plumage stages over a bird’s life can make identification of some bird species a challenge at times, especially juvenile, immature and non breeding plumage. However this adds greatly to what makes birds and birding interesting and it reflects the great diversity of our feathered friends.
Most birds start out life after hatching from the egg as featherless chicks. They quickly grow a covering of downy feathers which no doubt helps to keep the young birds warm while the parent/s are away gathering food. As the chicks grow the next set of feathers start to emerge through the down. The process of moulting natal down and growing the first covering of true feathers is known as fledging and birds at this stage of development are often referred to as fledglings.
Once a bird has its first set of true feathers it is ready to fly and is generally referred to as a juvenile. During this time the juvenile must learn to fly and fend for itself so it can gain independence from its parent/s.
Parent/s is used because in some cases the female raises the young birds with no help from the male parent – for example male Satin Bowerbirds play no role in raising their young – they are too busy displaying at their bowers. For some species the male is the sole parent, for example emu and cassowary. For most species however both male and female play a role in raising their young.
Young birds dependent on their parents are very vulnerable to predators while they spend many hours perched waiting for parent/s to return with food and as they take their first tentative flights. It is therefore not surprising that the first sets of true feathers are often very mottled and nothing like adult plumage – just what is required to enable them to blend in to the background and make them less obvious to predators.  The following photos show a number of juvenile bird species and their cryptic plumage together with photos of the adult birds for comparison.
A juvenile Jacky Winter perched waiting for its parents to bring food.
The cryptic feather pattern and colours helps this juvenile Jacky Winter blend in with the background.
An adult Jacky Winter
Juvenile Dusky Woodswallow.
Adult Dusky Woodswallow at nest.
Juvenile Eastern Yellow Robin.
Adult Eastern Yellow Robin.
Following the juvenile stage, birds moult their juvenile plumage and grow sub adult plumage, during which stage the young birds are sometimes referred to as immature. The birds become full adults when they grow their breeding plumage. This is obviously more apparent for male birds in dimorphic species (species where the adult males and females have different plumage).
Satin Bowerbirds are an example of this where the male looks like a female until three or four years of age when it develops a green throat, breast band and other subtle plumage changes. However it is not until the sixth year that the blue/black feathers start to emerge with full adult plumage achieved in the seventh year.
In a species where the male and female adult birds both have similar plumage, for example White-bellied Sea-Eagles, first year birds are juveniles and then over a number of years, when they are referred to first as immatures and then as sub-adults, they gradually lose the juvenile plumage, gaining full adult plumage at about five years of age when they are ready to breed.
These photos of Satin Bowerbirds and White-bellied Sea-Eagles illustrate the immature to mature plumage stage.
This Satin Bowerbird could be a female or an immature male?
This is an immature male Satin Bowerbird - note the green throat and fine white spots and streaks, the green band on upper breast and tip of bill starting to turn white.
This male has not quite reached full maturity - it does not have a full compliment of blue/black feathers however its bill seems to have turned fully white. This bird must be six going on seven years old.
This is a juvenile White-bellied Sea-Eagle.
This is a young adult White-bellied Sea-Eagle. It is about four years old and has passed through the first and second immature stages however it still has some light patches on the flight feathers so is not a full adult.
A full adult White-bellied Sea-Eagle.

While some birds retain their adult breeding plumage throughout the rest of their lives and through numerous moults to grow new fresh feathers, others grow and then lose their breeding plumage each year. For example male Fairy-wrens put on very colourful plumage for the breeding season but shed it and grow more somber plumage for the rest of the year – no doubt this is an effective survival strategy as bright plumage makes the adult males very visible targets for predators.
An adult female Superb Fairy-wren - note the reddish brown bill, lores and brow and brown tail feathers.
An adult male Superb Fairy-wren in non breeding plumage - note the black bill and blue tail feathers.
Adult male Superb Fairy-wren in breeding plumage.
Many of the wader species also grow and shed/moult breeding plumage each year,
This is an adult Double-banded Plover in breeding plumage. They breed in New Zealand and fly across the Tasman Sea to spend winter in Australia. This bird was photographed in late July at Byron Bay - it has developed breeding plumage ahead of its return to NZ.
A Double-banded Plover in non breeding plumage.
There are many more fascinating aspects to bird feathers and their function and maintenance during the course of bird’s lives – this post has just touched on the subject.

Monday, 20 January 2014

In extreme heat, birdbaths can become bird magnets

Last week southern Australia experienced a heat wave with four consecutive days of peak daily temperatures well above 40 degrees Celsius. For all warm-blooded animals heat stress can be a killer, so as we all know, adopting strategies to keep cool on extreme heat days is essential for survival.
Keeping cool involves a range of measures including reducing physical activity and staying out of the direct sun – that is seeking shade. In addition animal bodies have evolved ways of regulating internal body temperature. We humans do not have a cover of insulating fur or feathers that trap heat but we have sweat glands, which allow us to cool by evaporation. 
Many animals and certainly birds do not have sweat glands so on hot days dogs for example can often be seen panting and most birds are seen breathing through open beaks. This allows for a certain amount of evaporative cooling, however this comes at a cost – loss of moisture from the body with the associated need to keep hydrated. So on very hot days birds tend to reduce physical activity by roosting in the shade and making many visits, at least for some species, to drink at their favorite watering point/s. Of course some bird species seem to be able to survive without drinking water – they obtain all the moisture they need from their food.
Outdoor bird photography on extreme heat days is generally not on for a range of reasons and in any case the birds are generally lying low. However the need for birds to keep hydrated means birdbaths or other fresh water points can be very productive places to spend time observing and photographing birds on very hot days.
So for a couple of hours on two of the extreme heat days I set up in the shade by a long established birdbath to see which birds came in for a drink and or a bath.
Birds obviously have favorite drinking and bathing spots they use on a regular basis. Even with familiar water points most birds still approach them with caution and are often very nervous when drinking and bathing. Clearly predators including predatory birds have learnt that watering points can be productive sources of bird and other animal prey and the prey species know this, hence their nervous behavior.
This behavior raises an important animal/bird welfare issue – our presence at a watering point may keep wary birds away from water critical for their survival. This is particularly important when the water point is small and the only one for miles around. So whether we are simply setting up near a water point to observe or photograph birds or other animals, or perhaps when on holidays or travelling, we may be tempted to camp near a water point, we need to spare a thought for the animals that are using the water and ensure our actions are not keeping them away from water critical to their survival.
The birdbath I observed was located in a house garden and the birds had adapted to the presence of humans so my presence some six to eight metres away on a verandah semi concealed behind some shrubs did not seem to trouble the birds at all. In addition there were other sources of water nearby.
Over the few hours I watched the birdbath, thirteen species of birds came in to drink. The odd bird had a bath, however overwhelmingly they were drinking. I suspect many birds made repeat visits for a drink at short intervals.
Photographs were difficult under the dappled light conditions and in addition the bird’s nervous behavior and behavior towards one another added to the difficulty as they  moved about a lot. There were often two or three species present at the bath together. While there seemed to be plenty of room for all, clearly many birds had a low tolerance for other birds that were too close, so the odd squabble broke out. 
The birds moved about on the rim of the bath making me wait to capture photos of them in the sunny patches. Here are some of the photos I managed to capture (click on the images to enlarge).
Sharing or not sharing?
Spotted Pardalotes were frequent visitors to the birdbath. This may be a family group with one adult female in the foreground and two juvenile females behind - they were happy to share the birdbath.
Three White-naped Honeyeaters and one Brown-headed Honeyeater share
a section of the bath as a Striated Pardalote departs.
With all of the bath to share this Eastern Spinebill has emerged from a bath too close to a Silvereye which has its head feathers ruffled in protest. The Spinebills' head feathers also look to be raised?
 This pair of Honeyeaters, a New Holland on left and a White-naped,
argue over one small section of the birdbath.
The New Holland above has suddenly departed, ending the altercation and leaving
the startled White-naped to scramble back onto the bath.
Birds coming and going were often cause for concern among the nervous birds at the bath.
Here a Spotted Pardalote comes in above a Striated Pardalote.
Nervous birds keeping an eye on the sky?
Nervous birds at the bath often looked up to check the sky for predators.
This is a young Spotted Pardalote.
This Striated Pardalote is checking the sky for danger. Note the yellow spot on wing - this is the Tasmanian sub species striatus which is a winter migrant to mainland Southeast Australia between March and October. With the extreme heat wave this bird may be wishing it had made the trip
south across Bass Strait to spend summer in Tasmania?
This Silvereye is not looking at the camera, it is checking the sky above and behind for danger.
The following shots are more or less arranged in order with the most numerous and frequent visitors to the bath first. 
The White-naped Honeyeaters were numerous and visited the bath often in small groups.
A pair of Brown-headed Honeyeaters, the bird on the left is a juvenile - note the bluish eye ring.
Spotted Pardalotes came in often to drink - this is the very handsome adult male.
A male Striated Pardalote - this is Southeastern Australian mainland sub species ornatus
- note the red spot on wing.
An adult Eastern Spinebill ready for a drink.
When the New Holland Honeyeaters were not at the bath drinking and bossing
the other birds around, they fed on nectar in the Agapanthus beside the bath
- very convenient for them with both food and water in one location.
A juvenile Willie Wagtail - note the brown feathers on the wing.
Dusky Woodswallows came in as singles or in small family groups.
A juvenile Dusky Woodswallow - this bird was raised in a nearby woodland.
There were good numbers of Yellow-faced Honeyeaters around however this
was the only one I observed come into the bath.
I could hear a flock of Silvereyes nearby, however only a few came to this bath to drink.
There are other water sources nearby so there was plenty of choice.
This Grey Shrike-thrush was one of the larger birds to come to the bath.
It is wary and checking above for danger.
A Red-browed Finch catching a small patch of light.
I was surprised that only one Thornbill came in to drink. I have seen up to four species
come in together at our other birdbaths. This is a Striated Thornbill.
The above thirteen species came to the birdbath while I was there. A pair of Common Blackbirds also came by, but were very wary as  they always chose to drink and bath at a nearby bath.
The male Common Blackbird is an introduced species. He and his partner below were busy feeding young still in the nest. In between ferrying food they stopped often to drink and bath to cool down at a nearby birdbath which I could see from where I sat. Note the open bill in the heat.
The female Common Blackbird, mate of the male above. It was hot work for the pair feeding young. I suspect they were also taking water to the young in the nest.

Wednesday, 8 January 2014

Australian Darter

Darters, the denizens of fresh water wetlands, are, to me, fascinating birds.
A male darter with view of back.

Another male darter - view from front.
Superficially darters appear to be closely related to cormorants however observation and some reading show they are very different from cormorants in many ways. Some taxonomists still include darters in the closely allied cormorant family, Phalacrocoracidae, however today darters are generally seen as a distinct group of birds comprising the family Anhingidae. The family is widespread in suitable habitats in both the New and Old Worlds.
Do darters share a relatively recent common ancestor with cormorants or have they arrived at the current point of similarity from a more distant ancestor through convergent evolution?

The main similarities are:
·      both occupy the same freshwater habitats
·      both have webbed feet and swim underwater to capture food
·      both can be found with outstretched wings drying out after an underwater feeding session, often sharing the same perches
However darters are significantly different in the following ways:
Darters have wing and tail feathers but the rest of the feathers on their bodies look more like fur, allowing them to remain underwater without the need to swim rapidly and aggressively to overcome buoyancy as cormorants do.
This feature underpins the different feeding methods of darters and cormorants. Cormorants actively chase and grab prey underwater by snatching with their hooked bills. Darters are lone hunters stalking prey slowly underwater – buoyancy would make it difficult to remain submerged for this hunting method.
They use their long sinuous neck and long sharply pointed bill to spear fish. The neck can be kinked and then suddenly straightened in a darting or thrusting manner, a little like egrets fishing, but instead of above the water, darters fish underwater. Unlike cormorants, darters shed all of their flight feathers at once, rendering them flightless during moult.
Darters often soar to great heights using air thermals - cormorants rarely do this.
Note the long sharp bill and fur like body feathers which help to reduce trapped air and reduce buoyancy.
Another close up head view - note the prominent white slash behind the eye and fine dry body feathers which look like fur.
A female Darter drying feathers - note flight feathers on wings and tail and the rest of the body is covered in fur like feathers.
Note the long neck which even when stretched out has a kink - this mechanism is used to thrust the sharp bill forward to spear fish.
When hunting, darter’s bodies ride low in the water or completely submerged with just the long snake like neck protruding, hence one of the bird’s common names – snake bird. Needle-beak Shag is another common name for this bird. The family and genus name Anhinga originated from indigenous people in what is now Brazil. Their name, which was modified by the Portuguese, meant demon or devil. It is hard to see how Anhingas earned the name devil bird?
The different common and scientific names given to the darter in Australian text books, field guides and bird lists, for example Australian Darter or sometimes Australasian Darter and Anhinga melanogaster or Anhinga novaehollandiae points to different views by taxonomists – are the Australian birds a separate species from other Old World birds?
The Anhingas in South America, New World birds (Anhinga anhinga), are a separate species - they look a little different but occupy similar habitats and behave the same – see photo below. 
The current view (refer HANZAB - see references below) seems to be that Old World Anhingas should be separated into three species - so there are four species of darter worldwide.
A New World Anhinga. This bird was photographed from a canoe while looking for Giant Otters on an oxbow lake in the Peruvian Amazon in 2011.
So next time you are in a freshwater wetland habitat keep an eye out for Darters. Even experienced birders can miss a single darter perched among a group of cormorants or a lone bird hunting with just a needle beaked head and snake like neck visible above water.
The following three photos show the female bird in above photos in a "taking flight" sequence.
A Darter's low buoyancy makes remaining underwater for fishing easy but when wet getting airborne is difficult. This bird is nearly dry - even so it still struggles to gain height.
Even after several wing beats this bird is still kicking the water for some assistance.
Further along and the bird is still close to the water - note the neck is kinked in flight.

After publishing the post earlier today I received some comment and photos by email from a friend and fellow bird photographer. The photos, taken in Kakadu National Park show a Darter with fish it has speared. They are so good and show perfectly how Darters spear fish that I thought they should be included. John Saxton has agreed to this so here they are. Thanks John.
The Darter is a female, she has speared this fish with her lower mandible.
This fish has been speared with both mandibles. Having skillfully captured the fish it is then flicked into the air and caught head first and then swallowed whole - another very skillful maneuver. All bird species swallow fish head first to avoid the spines being caught in their throats.
The following texts were used to prepare the notes for this post:
S M Marchant and P J Higgins, Handbook of Australian, New Zealand & Antarctic Birds (HANZAB), Volume 1, Ratites to Ducks
T R Lindsey, The National Photographic Index of Australian Birds, The Seabirds of Australia
G Pizzey and F Knight, The Field Guide of The Birds of Australia
M Morcombe Field Guide to Australian Birds
K Simpson and N Day, Field Guide to the Birds of Australia
I Fraser and J Gray, Australian Bird Names – A Complete Guide
Christidis & Boles 2008 List of Australian Birds
BirdLife Australia Working List of Australian Birds