"STRICTLY NOCTURNAL" SNAKES … ARE THEY ALSO DIURNAL
Originally Published in Litteratura Serpentium 24(2) June (2002):80-93.
The traditional diagnosis of most snakes being either "nocturnal" or "diurnal" is generally flawed.
The thermal and feeding requirements of most snakes necessitate activity both by day and night, even for species traditionally regarded as being strictly nocturnal.
Even species only ever found actively moving about at night may be diurnal in terms of overall feeding and thermoregulation activity. The nocturnal movement over open areas and from refuge to refuge may only consist of part of the reptile's activity cycle and may be a result of the vulnerability of the reptile to attack when in the open.
Hence the diagnosis of many species as being nocturnal may be flawed.
Many species of reptile have for many years been regarded as being strictly nocturnal. This is especially so for some snakes.
What follows is a re-assessment of this theory in terms of certain species of Australian snakes.
While the analysis and commentary here relates to a select few species, there is little doubt that the same applies to most other Australian species and by extension also many overseas varieties.
This re-assessment is based on knowledge of the thermal and feeding requirements of the snakes, in combination with observations of specimens in the wild and in captivity.
DEATH ADDERS (GENUS ACANTHOPHIS)
Many texts report these snakes as being nocturnal. For example O'Shea (1996) described Death Adders (Acanthophis spp.) as "A nocturnal snake".
My own experiences in terms of capturing these snakes active as documented by Hoser (1989) and Hoser (1996) also reflects this.
By driving along roads in suitable habitat on warm nights in warmer months it is possible to find specimens moving about. There is no other time that one tends to find Death Adders active and in over 30 years of searching for these snakes, I've never found one moving about by day.
One such case involving an adult caught by another person was reported by Hoser (1981), and more on this case is mentioned shortly.
While most night active snakes are adult males in search of mates, other age classes and even females (of all age class) are sometimes found.
As already mentioned, Death Adders are almost never found moving about by day.
Hence it's not surprising that the view has formed that these are nocturnal species.
However a re-assessment of these snakes reveals a different picture.
Shine's and my own studies on gut contents of wild snakes has shown that these species often feed on diurnal species.
Refer also to Hoser (1981), where a diurnally active snake was caught having just fed on a large Eastern Water Dragon (Physignathus lesueurii) which is also a diurnally active species.
While it's always possible that these snakes may actively seek out their prey at night and attack and eat sleeping animals, this doesn't reconcile with the known feeding biology of Death Adders.
While some juveniles may actively search for food, adults are effectively always ambush predators. These snakes are simply too slow and heavy to be able to chase anything edible (in the wild state).
That is they must capture prey by ambush. They lure their prey by wriggling and twitching their tails.
So fixed is this means of feeding, that in captivity a Death Adder will wriggle it's lure for hours in order to attract a mouse or other food item placed in the same cage.
The snake will not as a rule crawl across the cage to find and eat the food item, even if it is within the snake's line of sight and even if the item is dead. Instead the snake's luring will become more intense.
In other words the idea that these snakes would move about by night in the wild searching out hiding spots for diurnally active prey simply doesn't seem likely.
Thus assuming that these snakes are strictly nocturnal as stated by texts such as O'Shea (1996), the question then begs, how do they manage to find and eat a largely diurnally active diet?
This is perhaps best answered by observing these snakes in captivity.
In captivity, these snakes tend to rest in a single spot in their cage and will actively lure during daylight hours.
This clearly shows that the snakes are awake and seeking to feed by day.
In cages with a well defined diurnal cycle snakes will be observed to move about the cage in order to sit in a site of preferred temperature. They will not however as a rule be seen moving about their cage in a searching manner.
In other words, the snakes are rarely seen actually moving, unless being watched constantly. However they will be noticed to have moved from one site to another adjacent site if viewed in the cage at different time intervals.
In other words by day these snakes are active, but only in terms of thermoregulation and feeding.
Because Death Adders are almost impossible to find by day, a comparison with wild snakes is almost impossible to make.
However at Tiddy Widdy Beach, immediately north of Ardrossan, South Australia, comparative observations can be made.
Here numbers of Death Adders (Acanthophis antarcticus) are large and due to the relative lack of cover as compared to other Death Adder infested areas, these snakes are relatively easy to find. This is particularly so during the warmer months when these snakes are most active and visible.
The sites where the snakes are found by day are usually under trees and other vegetation where the snakes are able to thermoregulate and yet remain "protected" by the overhanging vegetation.
Within this "site" or a few metres of a given point, the snake is able to remain still or only move slightly in order to thermoregulate by moving between sun and shade.
Simultaneously the snake is also able to site itself on a "run" whereby smaller prey animals such as skinks and birds may forage or pass.
Observations on these snakes by day in the wild state has shown that as in captivity, the snakes will move short distances to thermoregulate, but will not move across open ground as they do by night.
In other words a snake found occupying a site under a shrub or tree will remain there all day, but may move about within this site.
Because of their stout build and slow-moving ability across open ground, it appears that the lack of long-distance movement in these snakes by day is a simple defensive action to avoid being preyed upon by day.
Furthermore, and as already mentioned, these snakes are simply too slow to be able to chase prey across open ground.
The observed nocturnal activity (usually on dark moonless nights) is therefore an adaptation to avoid being eaten rather than indicative of strictly nocturnal behavior as had been thought. Furthermore, based on the nature of the snakes being caught, it's reasonable to infer that the movement observed at night is within the genre of relocation for the purposes of finding new feeding sites (to ambush food), to move to defecate away from a resting site or in search of a mate, none of which fit the category of general day-to-day activity.
Hence it's not surprising that in cooler southern regions, snakes such as Death Adders may only be found actively wandering on the occasional hot night and not necessarily day after day.
Noting the heat-loving nature of these snakes, it appears that not only may Death Adders actually be more active than previously thought by day, at least in terms of actively seeking food by luring, but if studied over a 24 hour period, one may well find that diurnal "activity" may in fact exceed nocturnal "activity" in terms of the snake either thermoregulating while awake and/or seeking food by luring with it's tail.
LITTLE-WHIP SNAKES (GENERA SUTA, UNECHIS, CACOPHIS, FURNINA, RHINOPLOCEPHALUS)
These snakes are (like Death Adders) also seen in warm weather crossing roads at night. Hence most texts also report these as being "nocturnal" species.
At cooler times of year they are found sheltering under exposed (to sun) rocks, particularly in spring.
Like Death Adders, these snakes are sometimes ambush predators, even though they do not as a matter of course engage in tail twitching or luring.
Again in captivity, these snakes show no aversion to feeding by day and like Death Adders, their diet is strongly skewed towards diurnal species such as skinks.
Noting that these snakes are found by day under exposed rocks and other surface litter, including fallen trees, leaves and hummocks, it appears that these snakes also seek out warm sites that affect protection from predators such as birds and mammals, but enables them to either ambush or stalk their small (mainly skink) prey.
Nocturnal activity in warm weather may for these snakes be the safest means to travel over distances to seek out new feeding or breeding areas. In fact, these times of activity in the warm months may well represent the only major opportunity for these snakes to move to new areas of any distance away from where they happen to be.
In captivity, these snakes have been observed by day to move to different locations under their cover, presumably to theremoregulate.
Assuming this to be the case in the wild, once again we find that "nocturnal" species are again being active by day.
Noting the preferred activity temperatures of these snakes, usually being in the high 20's to low 30's (° Celsius), and likewise for the Death Adders as already mentioned, it appears that diurnal activity in these "nocturnal" species may not just be an alternative activity pattern for them, but instead the only available activity time for these species for most of the year. This is especially true in southern Australia where for all but the warmest months, night time temperatures are too low (well below 20° C) to allow for nocturnal feeding activity by these snakes.
OTHER AUSTRALIAN SPECIES
Similar appears to apply for a number of python species, including those of the genera Antaresia and Morelia, both of which are often ambush predators.
While they usually are only found moving across open ground at night, they are also clearly diurnal.
In cooler and spring months, these snakes are often found thermoregulating and basking in the open or in crevices that get direct sunlight.
While it appears that these species also feed extensively on nocturnal species, they also eat diurnal ones as well.
Hence it appears that thermoregulation and feeding are daytime activities and that relocation and feeding are also done at night.
THE NEED TO MOVE
That snakes must move at night is essential.
They do not as a rule have a strong scent (smell), even as compared to most lizards. This is no doubt an adaptation to avoid being detected by prey items, especially in the case of those species that are ambush predators.
However all must defecate at some time and everyone knows that snake feces do have a strong odor.
After defecating the snake must move away from the site of defecation so as to avoid being detected by either prey or predator.
At Ardrossan, shrubs with fresh Acanthophis feces don't tend to have Acanthophis resting adjacent. The inference here being that the snakes themselves know of the risks and either deliberately or instinctively move away from it.
This makes the timing of defecation important and is one reason why snakes must run the risk of predation by moving about, including at times over open ground in order to flee their own wastes.
Species that may otherwise feed and thermoregulate diurnally, may find advantage in moving about long distances at night and hence over the years have been identified by people as "nocturnal" when in actual fact the bulk of their waking and activity is during daylight hours.
Storage of feces until time of movement no doubt also occurs.
In the captive situation this manifests in the snake that is taken from a cage and allowed to roam a large room. As the snake crawls about the open ground it will defecate. It will not as a rule defecate where it rests.
Alternatively, it is relatively unusual for a snake to defecate where it rests unless it is kept in a particularly small cage, in which the case the snake will find it is unable to move away from it's defecation site and hence may actually pass feces where it usually basks.
Based on the above, it appears that for many snake species, there is an apparent reluctance of snakes to take the risk of moving across open ground. Obviously the situation is that this is a time of high risk for the snakes.
As snakes must move about to slough, it is therefore not surprising that this is also an opportune time to defecate. Hence it's not altogether surprising that many snakes will store feces about this time in order to defecate when they shed.
For some species, Death Adders included, non-defecation at sloughing time (+/- 24 hours) is so rare as to be unusual and worth putting on a given snake's husbandry records if it occurs.
Hoser, R. T. 1981. Note on an unsuitable food item taken by a Death Adder (Acanthophis antarcticus)(Shaw). Herpetofauna 13 (1):31.
Hoser, R. T. 1989. Australian Reptiles and Frogs. Pierson and Co., Sydney, NSW, Australia:238 pp.
Hoser, R. T. 1995. Australia’s Death Adders, Genus Acanthophis. The Reptilian 3(4):7-21 and cover, 3(5):27-34.
O’Shea, M. 1996. A Guide to the Snakes of Papua New Guinea. Independent Group Pty. Ltd., Port Moresby, PNG:251 pp.
Raymond Hoser's been at the leading edge of herpetology in Australia for some decades. He's authored over 150 articles and papers and nine books.
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