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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