Pecking orders in large venomous Snakes from South-east Australia ecological and distributional Implications.

 

Raymond Hoser

488 Park Road

Park Orchards, Victoria, 3114, Australia.

E-mail: adder@smuggled.com

First published in hard copy in Boydii (Journal of the Herpetological Society of Queensland), Spring 2005.

Also published in hard copy in Litteratura Serpentium (Journal of the European Snake Society), 26(2):142-156, June 2006.

ABSTRACT

Australia's large elapids all have similar habits in that they are generalized predators and occupy a wide range of potential habitats where they occur.

Noting that most appear to be solitary most of the time and that they apparently compete for food and habitat, the pecking order between species must have a major impact on where they occur and perhaps even their daily activity patterns.

This paper demonstrates a predictable pecking order between the four dominant elapid genera (and most common species in each genus) in south-eastern Australia. From top to bottom it runs, Pseudonaja (textilis), Notechis (scutatus), Pseudechis (porphyriacus) and then Austrelaps (superbus/ramsayi). Furthermore, in the same pecking order, the pythons appear to outrank the elapids and within pythons, Olive Pythons (Liasis), outrank the Carpets (Morelia).

This pecking order directly impacts on distribution of species within a given area or habitat and is important in terms of housing more than one captive snake in a cage.

INTRODUCTION

In the period 2002-2004 I was the only "Snake catcher" listed in the Melbourne telephone book. (In the 2004/5 phone book a novice catcher has also listed himself as a "snake handler"). As a city of 3 million inhabitants in one of the more snake infested parts of the world, (Australia), it stood to reason that I would get a large number of calls to catch and remove snakes.

In Melbourne, the dominant species is the Tiger Snake (Notechis scutatus), which more than any of the others has managed to survive and prosper in heavily urbanised areas, such as the inner suburbs around the Yarra River and Tributary Creeks (Hoser 1990).

The Brown Snake (Pseudonaja textilis) is most common in the north-western suburbs and the Copperhead (Austrelaps superbus) most common in the far east and south-eastern suburbs.

The limiting factor on snake numbers in Melbourne seems to be the fact that there is a lack of suitable habitat and even in relatively uninhabited outer areas, there is a general lack of suitable hiding spots with a sunny enough aspect to satisfy the thermal requirements of these reptiles (Melbourne is in Melbourne's south).

Brown Snakes as an egg-layer appear to limited by temperature and habitat in that cooler suburbs of Melbourne apparently lack suitable areas to lay and incubate eggs or lack suitable habitat in terms of the high preferred activity temperature for the species.

While Copperheads are a cold climate species, they are found in or near most parts of Melbourne (the species in southern Victoria being A. superbus) and distribution appears to be dictated in large part by the presence or absence of other species (see later this paper).

In terms of climate however, no part of Melbourne is too warm for the species.

By default, copperheads are most common in areas lacking other snakes. This reflects both their tolerance for cold as well as the fact that other snakes tend to be higher in the so-called "pecking order".

Three other small elapids found around Melbourne (Rhinoplocephalus nigrescens, Drysdalia coronoides and Suta flagellum) are generally not seen by non-collectors and while numerous where they occur are rarely encountered by non-herpetologists and generally don't move into inhabited areas in the same way that the larger species do. Put another way, they don't travel great distances.

These smaller species are radically different in size class (never over 60 cm versus commonly over 100 cm for the other three species) and of average bulk less than a tenth of the "big three" and hence do not compete against them in any meaningful way.

As snakes eat other snakes when the others are small enough, the innocuous species (Rhinoplocephalus nigrescens, Drysdalia coronoides and Suta flagellum) would presumably either tend to avoid the other species or risk getting eaten.

Hoser (2001 and 2004c) showed that in northern Australia, two species, Taipans (Oxyuranus scutellatus) and King Brown Snakes (Cannia australis) competed with one another where they co-existed and that by and large Cannia australis was at the top of the pecking order when specimens of similar size class clashed.

It appears that they may have literally eaten Taipans out of existence in many parts of their former distribution in northern Australia in the 20,000 years preceding European settlement of Australia.

In south-eastern Australia, four species (or genera), namely, the Brown, Tiger, Copperhead and Red-bellied Black (Pseudechis porphyriacus) appear to be very similar in size class (all about a metre) and ecology in that they are large generalist elapids.

Until now, the general perception has been that the main determinant of distribution for these snakes has been climatic and habitat.

In terms of broader distribution, this most certainly appears to be true.

For example Copperheads are common in coolest places and in some areas are the only species present (e.g. most of the alpine regions).

In slightly warmer areas (such as Melbourne), three of the "big four" occur, the notable exception being the Red-bellied Black Snake, which while listed as a Melbourne species appears to be virtually absent from the city.

Most reports of this species appear to be of similarly coloured Copperheads, including all so-called "snake rescues" for Red-bellied Black Snakes.

I received a call for a genuine Red-bellied Black Snake at Broadmeadows, a northern suburb in 2003, but this snake was not near any bushland, paddocks or other habitat and had presumably stowed away in a car or crate or similar and hitched a ride from elsewhere to Melbourne.

Such cases occur frequently, not just from snakes outside of Melbourne, but also more commonly by snakes within Melbourne.

The most common situation is snakes crawling into a parked car's engine and then alighting once the car has driven elsewhere.

The second most common situation is snakes hitching rides in boxes of fruit from northern regions, including northern and far eastern Victoria, which is where Red-bellied Black Snakes are more common.

Brown Snakes like grassy and open habitats and avoid colder places and hence it is not surprising that they are rare or non-existent in southernmost parts of Eastern Victoria.

Red-bellied Black Snakes are found in riparian habitats throughout the eastern third of Victoria, but their distribution becomes patchy from just east of Melbourne and westwards, although an isolated population of the species is found in south-east South Australia.

That population may be linked via the lower Murray River Valley, although Museum specimens don't show specimens from the area.

The lower Murray River Valley does have a large number of Tiger Snakes (especially historically), even though it has declined sharply in the latter half of the 20th century and this may in part explain the absence of Red-bellied Black Snakes from this area (see this paper).

Based on my experience as a "snake catcher", it has become clear that as a rule snakes don't like their own kind.

In the Australian context, aggregations are so unusual as to warrant papers being written on them (e.g. Hoser 1980).

In terms of the "big four" (Brown, Tiger, Black and Copperhead), most specimens found are found on their own. On rare occasions a male and female may be found together.

Even when patches of good habitat occur, it is usual only to find one large elapid at a time.

The only exception is in the cooler months when more than one may be found hibernating in close proximity.

These sites are usually rare sites of good habitat with good northerly aspect, which in southern Victoria are sometimes hard for the snakes to find, and hence the aggregations.

One such overwintering aggregation of Eastern Brown snakes was found in a north-facing retaining wall, in an industrial estate just south of the Western Ring Road at Thomastown.

The discovery resulted when I was called to catch a single specimen seen basking at the top of the wall.

A similar spot exists near the Warrandyte Cemetery where every year numbers of Tiger Snakes turn up in a group of overgrown gardens near the south bank of the Yarra River (north facing slope).

Highest numbers turn up in the September/October period as the snakes emerge from hibernacula. Snakes appear to be of all size class.

THE BASICS OF THE PECKING ORDER

In the captive situation, establishing the pecking order of snakes has never been difficult. Generally it's been the big snakes rule over smaller ones.

On rare occasions where two snakes are of similar size, they may fight, with the stronger individual usually getting right of way.

In the cage situation, the stronger snake occupies the better hiding spot, while the other will tend to move away or if hiding spots are unavailable, merely mope in a corner.

Snakes kept as a group may tend to have the lines of their pecking order blurred, but if they are separated for some time, then the pecking order will tend to re-establish if and when they are reintroduced.

Males of the large elapids (the big four) all fight over mates (male combat) and hence will aggressively defend their pecking order if need be.

(Having said this, Copperheads don't bite one another when fighting (they hold heads apart) and based on a recent case involving a pair of sibling males that I held in a cage, in which one bit and killed the other (on 16 June 2004) they may not even be immune to their own venom).

Based on the pattern of snakes not liking one another in the wild, (they are usually found on their own), the observed pecking order of snakes in captivity, could reasonably be transposed to fit their wild counterparts.

DIFFERENT SPECIES

While it's been easy to use size as a basis to predict pecking order in a single species of elapid, it hasn't until now been possible to predict the pecking order between different species of large elapid (as in the big four), including among specimens of the same general size class.

In the captive situation, it'd be reckless to place specimens of different highly venomous species together. Should one bite another, it'd be likely that it wouldn't be immune to the venom of another taxa and hence the snakes may kill one another.

That in fact occurred in my own collection in 1971, when I had a juvenile Eastern Brown Snake bite an adult Red-bellied Black Snake and killed the Red-bellied Black.

Notwithstanding the above event (which occurred within the confines of a three foot cage) and occurred at a time when I was too young and inexperienced to know better, snakes generally bite as a last resort, not first.

This is evidenced by my more recent (2004) use of the big four species in "dangerous snake shows".

Against conventional wisdom I routinely place specimens of the big four together by placing them on one another on a small table and handle them in one or two hands as a group.

Outside the public showings, these snakes are free-handled on a day to day basis, shipped as groups (often all four species in a single box) and often housed for days on end as a bundle of up to a dozen snakes in a single cage.

This is possible and without deaths through bites (none so far) due to the fact that all the snakes were made venomoid using the method detailed by Hoser (2004a).

(Venomoid is the result of having the venom glands surgically removed, making the snakes effectively non-venomous).

The venomoid snakes apparently act normal in all ways, although their disposition to humans changes markedly following the operation due to the following factors:

1/ The snakes are "free handled" (mid body support without head or tail restriction) instead of tailed and necked, both of which stress the snakes considerably. For those unaware, the caudal region houses the genitalia of the snakes and picking up snakes from here sometimes stresses them quite considerably.

2/ Snakes tend to calm down when housed or moved about as a group.

Why this is so isn't clear, but it is the case. Part of the reason is that the snakes become far more concerned about one another than humans handling them and hence the fear of being handled declines.

Observable is that snakes actually become more agitated as they are put down after being handled as they reassess their physical position in terms of the other snakes.

Hence, it becomes clear that the snakes maintain a strong concern and awareness of one another.

This shows when the snakes move their heads away from one another as another approaches. The snakes do not however tend to bite one another except as a last resort or on rare occasions when movement is very rapid and a snake is unusually agitated.

Transposing the same situation to snakes in the wild state and it becomes clear that in establishing their own pecking order, bites would be rare.

Perhaps it's a case of the mutually assured destruction theory, whereby both snakes (of different species) would be aware of the likely death of both, should they decide to bite one another.

While it'd be fair to assume that size would be the simplest way to establish a pecking order among snakes (needed to decide which gets "right of way" or to occupy the better resting or basking sites), it soon becomes clear that size alone is not all that's used to establish pecking order among the big four.

THE EXPERIMENT AND THE RESULTS

The following results were not from a planned experiment, but rather what was routinely observed in the caging set-up used by myself.

As a matter of course snakes were housed individually. One some occasions, they were housed in groups of up to three for a given species (as in three Tigers or three Red-bellied Blacks).

In all cages, the set-up was the same.

Each cage had only one hide, in the form of an upturned pot or similar.

When conflict arose between snakes, the dominant (usually larger one) would occupy the hide and force the other/s out to sit in the open.

When using snakes for shows the snakes would be removed from cages and placed in smaller transport boxes (click clacks). At the end of the day, they'd be returned to their cages.

Because all the snakes were now "non-venomous" and apparently compatible, in that they didn't overtly fight or appear unduly stressed, they were sometimes housed in groups overnight in less cages, with up to 12 snakes per cage. This was generally done when I arrived home late at night and had another show starting early the next day.

It was easier to unload to one or two cages rather than a dozen or more, and likewise for the re-loading.

In terms of the big four species, it soon became clear that there was a well-established order of superiority among them. It ran as follows: Brown (top), then Tiger, then Black and then Copperhead at the bottom.

Why it ran like that, I had no idea, but that was how it ran.

I'll give some examples as to how this was determined.

One night, a single Eastern Brown, four Tiger Snakes, three red-bellied Blacks and a Copperhead were left in a single cage. Many immediately made for the hide (upturned pot).

The next morning, only the brown snake was underneath it. The rest of the snakes, including Tiger Snakes of considerably more bulk, were outside.

This pattern was generally repeated on numerous occasions.

If snakes were housed in the cage for several nights in succession, the order broke down in as much as other snakes decided to go into the hide and stay with the brown snake.

However if the snakes were housed on their own for a period and then regrouped the same set-up would re-establish itself.

If the Brown Snake was excluded from the cage, the larger Tiger Snakes would take over the hide.

Having said this, the other three deadly species all showed more tolerance to others of their own kind (other snakes and/or their own species) than did the Eastern Browns.

In another case a Red-bellied Black Snake (male) was placed with an ovulating Tiger Snake of similar size.

On that occasion at least, he wasn't interested in mating her.

At first the Black Snake simply crawled under the hide with the Tiger Snake.

A day later the Black Snake was seen moping in the open, where he remained for some days.

When placed back in his own cage, he immediately went back to his (identical) hide where he remained. In other words, it appeared that the Tiger Snake had forced the Red-bellied Black snake out.

When the same situation was reversed, (female Red-bellied Black and male Tiger), the result was the same, in that it was the Black Snake that was forced out of the hide.

In a similar set of situations, it became clear that the Copperheads were at the bottom of the pecking order.

DIFFERENT SITUATION, SAME RESULT

In the group cages, where up to a dozen snakes were literally placed as a mass and with little ground area, the higher ranking snakes invariably ended up on top.

Hence the bigger snakes tended to cover the smaller ones and the Eastern Brown would never allow itself to be covered with other snakes.

These trends weren't 100%, but they were consistent enough to be recognizable.

The same situation would be seen when several snakes would rest in a hide. The Brown Snake remained on top and interestingly the other snakes seemed to accept this.

There was no visible jostling for positions. The snakes seemed to know where they'd sit.

TIGER SNAKES VERSUS RED-BELLIED BLACK SNAKES AND COPPERHEADS

Based on the above observed hierarchy, we may have another factor limiting distributions of some snakes, albeit in a localized manner.

Where Tiger Snakes are in high densities, they may act to force out the Red-Bellied Blacks and Copperheads. This may explain why in parts of the lower Yarra Valley (Victoria), where Tiger Snakes clearly are abundant, no Copperheads occur.

Areas that fit this profile are suburbs downstream from Templestowe.

In terms of habitat, climate and so on, there is no other obvious reason as to why the Copperheads are apparently absent.

In parts of the lower Murray basin, Tiger Snakes were historically in plague proportions and yet there are few if any historical records for Red-bellied Black Snakes, even though the habitat appears suitable for the species. In Western NSW, the Red-bellied Black Snakes appear to be most abundant in areas of suitable habitat which either have no Tiger Snakes or where they are rare.

One such example is the Macquarie Marshes, north-west of Dubbo.

SUNBURY IN MELBOURNE'S NORTH-WEST

The suburb of Sunbury is about 35 km north-west of Melbourne. It is one of the better places to find the Eastern Brown Snake (Pseudonaja textilis). The species dominates this suburb. The distribution of Brown Snakes is constrained in south-east Australia by the fact that they lay eggs and hence do not occur in colder areas that can be invaded by the live-bearing large elapids (Black, Tiger and Ccopperhead).

In Melbourne, with a few rare exceptions, the Brown Snake species is restricted to the area north and west of the Yarra River, including Sunbury.

In Sunbury, the Eastern Brown Snakes dominate most areas, including the tops of the north-facing hills, such as that immediately adjacent to the new Sunbury Primary School. On 4 October 2005, I got a call to remove a large (1.8 metre long) Brown Snake from this site. Noting that this was perhaps the warmest site in the town, it was not surprising that a large Brown Snake had taken up residence here, perhaps forcing out smaller individuals and other lower ranking taxa, such as Tiger Snakes.

In Sunbury, the Tiger Snakes are apparently confined to the south-facing south side of the town (between the main urban area and the Calder Highway).

Noting that in the captive situation and in the wild state when there are no competing species, both taxa prefer to live in warm sites for most of the year, the only plausible reason for the Tiger Snakes being in the suboptimal area is the impact of the Eastern Brown Snakes forcing them away from better sites.

The alternative explanation (habitat preference) doesn't carry weight due to the fact that in other suburbs of Melbourne lacking Brown snakes, the Tiger Snakes move to the same sorts of sites as those taken by Brown Snakes at Sunbury.

DEATH ADDERS

A fifth elapid species of note in South-eastern Australia is the Death Adder (Acanthophis antarcticus).

These aren't found in Victoria due mainly to the fact that in the recent geological past the climate has been too cold for them. They are however found in nearby parts of NSW and South Australia (Hoser 1989).

They are more sedentary than the other species and hence it'd be reasonable to assume that they have a less established social order than the other snakes.

In the captive situation, Death Adders get very agitated when they have contact with any other snake, including their own kind. Aggravating the situation is that when agitated, they tend to just bite what's agitating them.

In a cage with their own species (or any others of the same genus) experience has shown that these snakes are immune to their venom. Hence the only consequence of a Death Adder meeting another of it's own kind is either a bite or perhaps sex, although for some species of Acanthophis, cannibalism sometimes occurs (Hoser 2004b)

In terms of other snakes, the situation isn't as pleasant.

Doing live snake shows, Death Adders tend to bite other snakes.

In fact this is common place!

If the Death Adders used in my snake shows (that are placed on top of other snakes) weren't venomous, I'd have lost several of my snakes by now from snakebite!

How they rank in the above documented pecking order I can't say. Suffice to say that they don't seem to have the social skills to even establish a pecking order, except perhaps among their own kind they simply bite anything they don't like!

This is not so much due to aggression on the part of these snakes, as they aren't terribly aggressive.

Rather this biting habit arises from the fact that these snakes don't like to move (for any reason) and when poked, prodded or crawled over, simply bite out of frustration.

PYTHONS AND OTHER VARIABLES

Because of the non-venomous state of venomoids, I was able to mix pythons with elapid taxa and observe their reactions. This included when different families were housed together for days at a time in a given cage.

While humans think of elapids as outranking pythons due to their venomous properties, it is evident that snakes themselves see things differently.

When pythons and elapids were mixed, the pythons were able to force the elapids out from their shelters in order to occupy the optimal habitats.

In my cages, this usually meant that overnight the pythons would stay under the upturned pot in the cage (the "hide") and the elapids would be forced to mope about in the open.

That the elapids didn't like this situation was shown when the pythons were removed from the cages.

Then the elapids would reposition themselves under the upturned pots.

In these examples, I am talking of snakes of similar size and not necessarily adults of all taxa.

If different taxa remained in the cage, then they would position themselves (or reposition themselves) according to rankings as already outlined.

In terms of pythons that were mixed, Olive Pythons (Liasis) would outrank Carpets (Morelia), assuming specimens were of comparable size.

These results as seen in captive situations do appear to occur in the wild as well. A perusal of past collecting records for most parts of mainland Australia showed that as a rule, the ground-dwelling pythons occupied the optimal hiding spots in areas that they occurred.

For the tree-dwelling pythons (genus Morelia), the picture in the wild is not so clear, although their hierarchical position in captivity is easily ascertained as being above elapids and below the other pythons.

In terms of sexes for all kinds of snakes, non-mating females would outrank males.

In such situations, the males would be forced to move on from the hide.

In mating situations, things apparently reversed in as much as females tended to run away from males, although this is not necessarily a reflection of the real hierarchy between the snakes.

ESTABLISHING THE HIERARCHY

As a rule combat or other physical interaction between the snakes of different species (or same species) did not occur. Even in species known to engage in combat (e.g. Browns, Copperheads and Blacks), such rarely occurred when establishing a pecking order.

It is clear that via non-physical means that snakes can establish their own pecking order among themselves and interactions.

In the wild this manifests as a tendency for snakes to be found on their own. They know to keep away from others of other taxa and most of the time their own.

In captivity, the hierarchy tends not to manifest in terms of different taxa due to the rarity of them being kept together.

In terms of the same taxa, the hierarchical arrangements between snakes can be an effective time-bomb for subdominant individuals when housed in group cages.

Those specimens will tend not to be able to bask in the preferred spots or thermoregulate properly. Coupled with the ongoing stress of having movements constrained by the mere presence of dominant snake/s, their long-term health prognosis may not be good.

There is little doubt that this hitherto largely undiagnosed hierarchical arrangement between all snakes has led to large numbers of deaths in group cages and outdoor pits as seen at many large zoos and reptile parks.

Noting the hierarchical arrangements seen, my own facility houses most snakes on their own (in separate cages) with grouping of snakes only for the purposes of transportation, snake shows and sometimes overnight when shows end late in a day and are to start early the next.

While short-term grouping of well-established captives of similar size class when not feeding appears to be of no serious consequence to the snake's health, there is no doubt that some snakes would suffer in the longer term.

This is even true for some specimens of relatively group tolerant species such as Tiger Snakes.

In terms of grouping, it seems that immature snakes are more tolerant of other snakes than are adults. This has been seen in both elapids and pythons.

CROSS-GENUS MATING

This has been observed, usually when a particularly highly sexed snake is aroused and then mounts the only other available snake. This may be of any species or sex!

Within these constraints, certain trends have emerged in terms of cross-species or cross-genus mating.

Generally, lower ranking species (using the above hierarchy) will allow themselves to be mounted by higher-ranking ones, whereas the reverse seems to be avoided.

Hence in September/October 2004, it was possible to initiate mating between a male Death Adder (Acanthophis bottomi) and a Lowlands Copperhead (Austrelaps superbus), but not between either of the following: A male Red-bellied Black Snake (Pseudechis porphyriacus) with a female Tiger Snake (Notechis scutatus) or a male Tiger Snake (Notechis scutatus) with a female Death Adder (Acanthophis antarcticus cliffrosswellingtoni).

The preceding union just described would not have led to fertlization as the male Death Adder had not been cooled sufficiently prior and hence would not have been producing viable sperm. This is known from prior experience in terms of breeding snakes of the genus Acanthophis.

END NOTE

While all the above species are apparently sympatric in parts of their distributions, it appears that for at least the first four (Brown, Tiger, Black and Copperhead), their pecking order may influence movements of individuals and in the longer term abundance in certain localities if and when suitable habitat for one or more species is in relatively short supply.

REFERENCES

Hoser, R. T. 1980. Further Records of Aggregations in Various species of Australian Snake.

Herpetofauna (Australia), 12(1), pp. 16-22.

Hoser, R. T. 1989. Australian Reptiles and Frogs. Pierson and Co., Sydney, NSW, Australia:238 pp.

Hoser, R. T. 1990. Melbourne's Snakes. Litteratura Serpentium, 10(2), pp. 82-92 and 10(3), 122-145.

Hoser, R. 2001. A current assessment of the status of the snakes of the genera Cannia and Pailsus, including descriptions of three new subspecies from the Northern Territory and Western Australia, Australia

Hoser, R. T. 2004a. Surgical Removal of Venom Glands in Australian Elapids: The creation of Venomoids. The Herptile 29(1):37-52.

Hoser, R. T. 2004b. The husbandry and breeding of Death Adders. Reptiles. September.

Hoser 2004c. The Great Australian Snake Extermination. Hard Evidence, 4(2):32-38 and 4(3):21-29.

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