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. |
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. |
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
Another really interesting post. One day I hope to see how that manage to get the speared fish off their bill and into the air.
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