Monday, March 12, 2007

Elapognathus coronatus, Western Crowned Snake

A nice looking snake, but difficult to photograph.

The Western Crowned Snakes seldom exceed 50 cm in length, but grow larger on offshore islands. On the mainland they are usually encountered in the morning, sunbaking or crossing sandy tracks. If you see one before you get too close, it will remain still and you can slowly approach to within camera range. However, if you don't see it and walk anywhere near, it will very quickly disappear into the vegetation, where any chance of a close encounter will be lost.

A Western Crowned Snake, caught hunting frogs.

Western Crowned Snake, Elapognathus coronatus

The above hunting photo is one of the more interesting as usually they resemble a slender stick on the track and I have many photos of stiff looking snakes without any interest or character. The one below is typical.

If you are lucky, a more interesting shot can be obtained as it rapidly heads off onto low vegetation, but capturing any detail is another matter, so not very appealing photographically.

I mentioned above that these snakes on offshore islands grow larger, which seems to conflict with the offshore island Tiger Snake, Notechis scutatus (see previous post 05), which are smaller than the mainland ones. So why is this? I suspect there is a critical mass for snakes in these island environments of around a metre. Any larger and they have difficulty finding enough food, but around this size is probably ideal to move around the environment and survive on their diet of skinks. Whilst on the mainland skinks are not so common, plus there is additional competion from larger snakes like the Tiger and Dugite (see previous post 06) who dominate the larger food items, ie larger frogs and small mammals. So the mainland Western Crowned Snake has adapted to prey upon the smaller frogs, with some skinks and possibly a few invertebrates. This niche it shares with the Bardick, Echiopsis curta (see previous post 02) and the Masters Snake, Drysdalia mastersii. The Western Crown Snake (unlike the other two) is endemic to WA and is found around the coast from the Great Australian Bight to a little north of Perth.

The coloration of reptiles can vary considerably and the crown snake is no exception. Typically the top of the head is a blue/grey, and across the back of the neck is a darker band that extends forward and passes through the lower part of the eye, to the snout. Below the eye, the upper lip is prominently white. The eye pupils are also distinctive, being round and circled by a lighter colored ring.

With some crown snakes the top of the head is much darker and similar in color to the dark band, making identification from this feature alone difficult. However they still retain the prominent white upper lip and the eyes remain the same.

Being largely a frog eater, this snake favours wet/dry heath, which is a common habitat in the Esperance region and explains its abundance here. It seeks shelter under logs and rocks, plus in the abandoned nests of stick-nest ants (pictured below), which are also common in the district.

A snake doing what a snake does!

Hello! Hello! What's going on here then?

Animals and plants are interrelated with each other and the environment; they occupy a niche that is governed by other members who collectively make up their eco-system. If you remove a portion, like an animal or plant species, even logs or rocks, this can affect the entire eco-system and destroy the fine balance required to maintain it. So please think carefully before you cause change to natural environments.


huntervalley said...

That's a beaut little snake. If I had snakes showing themselves regularly around me, I would rather they be nice little ones like that than the Eastern Browns and Red-bellies we get here.

Perhaps you can clear up some questions on snake eyes: I have read that venomous snakes have elliptical pupils and non-venomous snakes have round pupils. But I notice that tigers (venomous) have round pupils, and pythons (non-venomous) have elliptical pupils. So obviously the information that I read (in a couple of places) is incorrect, or at least the identification characteristics are inconsistent.

I have also read that most snakes with elliptical pupils are nocturnal.

Can you shed any light on the round vs elliptical pupil in snakes?

I am enjoying learning about the nature from your area. Your photography is excellent.


Esperance Blog said...

Hi Huntervalley, I have checked out the pupil shape of the snakes I am most familiar and all bar the Bardick, Echiopsis curta, have round ones.

The Bardick has vertically elliptic pupils. This is a venomous snake (Elapidae), so obviously it does not indicate that a snake is venomous or not.

However the Bardick is largely nocturnal, so it may aid this snake to see at night. Having said that, the Tiger Snake, Notechis scutatus, has rounded pupils and is often very active at night. So do you have any evidence that the shape of the pupil aids night-time vision?


huntervalley said...

No, Jack, I have just been interested in why some snake pupils are round and some ellipitic, so have been doing some reading on the internet, but I didn't find any reliable reading on the subject.

There are so many mysteries in the world of nature :)


Esperance Blog said...

Me neither Huntervalley, but must keep an eye open for any information in this regards.


huntervalley said...

I contacted the Australian Museum (Sydney) and asked of round pupils and elliptical pupils and this is the museums reply:

"Diurnal snakes typically have round pupils and moderate-sized eyes. Nocturnal snakes typically have large eyes and many also have vertical elliptical pupils.

Round pupils can close tighter in bright sunlight. Vertical pupils can open wider in dim light to improve hunting ability.

Pupil shape is linked to habits and habitats."


Esperance Blog said...

That is very interesting Huntervalley, thanks for going to the trouble of chasing it up. I wonder how it relates to frogs, as some have pupils that are slit horizontally, whilst others have vertical ones?


Anonymous said...

What an interesting blogspot..We came across one of these Crown Snakes this morning in Albany, and having never seen one before, had to look on the internet to identify it. Funny little things, quite different to the usual tiger snake sightings - very stick-like and didn't move whilst being photographed.