The defining features of a successful predator are strength, speed and patience. Of course there are a whole suite of other features that assist in the strategies that successful predators use including camouflage, decoys and attractants, specialised anatomical features for capture and holding, hearing, smell, touch and usually superb eyesight. Some have even developed the ability to construct traps, from the simple pits of ant lions to elaborate and complex webs in the case of the spider. But none of these unlike the preceding three are obligatory.
The other day those features of speed strength and patience were demonstrated in a way that surprised even me. While walking along the edge of a patch of subtropical rainforest I noticed a commotion in a large sandpaper fig as a male grey butcherbird pursued a female. Now these are highly specialised and very effective predators, a member of the group of corvids that include magpies and currawongs. It is a medium sized bird about 30cm long (beak tip to tail tip) with a well developed hook at the end of the upper beak. This is a special adaptation that helps a toothless animal capture and hold its prey. Prey species are mainly small birds and nestlings although a wide range of insects and other small vertebrates make up a reasonable part of the diet. While there are 2 species that are found in monsoonal and tropical rainforest the grey and pied butcher birds have successfully colonised Tasmania and most of mainland Australia. These are highly successful predators that would be commonly seen by the most casual observer. Even if not seen, their beautiful melodious song would be even more familiar.
But back to the fig tree. The female butcherbird was being vigorously pursued by the male and then seemed to abruptly stop in mid air and could be seen suspended and weakly flapping its wings. How strange, the male flew back and fluttered agitatedly nearby. Was this some strange partnering/mating strategy? I went to investigate.
I was stunned to find that a carpet python about 2 metres in length was suspended from a branch and had caught the bird in mid flight. Presumably it had caught it in its mouth but by the time I got there it already had a couple of coils around its prey’s body thus limiting its ability to flap its wings. Ingestion started immediately. Notwithstanding the fluttering and calls of the male bird the python continued its meal unperturbed.
That the python had the strength and speed to pluck a fast flying medium sized bird from the air was impressive. But the patience needed to wait, hanging about 1/3 of its body from a branch on the off chance that a bird would fly within reach was stunning. It seems highly unlikely that this was just a result of chance alone, if this assumption is true then laying in wait for a bird to fly by must be a regularly used hunting strategy. Or was it experience that told the python that the mating ritual of this species meant a much less alert prey and that with patience the possibility was there that a mid flight capture was possible?
Providing a predator is of reasonable size, that is its body weight:surface area ratio is high and has a resulting low metabolic rate, then the concentrated nature of their food means that the animal, unlike herbivores and omnivores, does not need to eat frequently and if you are a reptile and therefore a poikilotherm (“cold blooded”), not very frequently at all. Some shrews weigh just a few grams have a low body weight ratio and an extremely high metabolic rate accentuated by their intense predatory (and predation avoidance) activity. This means they must eat more than their body weight of high protein value food each and every day just to survive. The effect of the meal that our python had would probably have lasted for several weeks and on that basis extreme patience could be afforded. The interesting thing is that unlike homeotherms the metabolic rate of poikilotherms and therefore their need for food drops as the temperature reduces. This is the reason why forced feeding of reptiles while undergoing veterinary care should be approached with great caution. Over zealous feeding especially during periods of low activity and/or low temperatures can result in intestinal stasis and decomposition of food in the alimentary tract with serious and even life threatening consequences.
So the hunting strategies and adaptations of predators are highly varied and in many cases highly complex with even some of the least likely methods being abundantly rewarded. Species are only successful when the survival strategies of individuals (or individual groups) allow them to survive and leave offspring that can fill the habitat that is available. It is not in the interest of predators to eliminate their host species and in most cases a predator/ prey balance is struck. If a prey species drop in population the predator’s habitat contracts and its population declines or they move to a new area until prey numbers recover and the old balance is restored. The exception here is of course human kind. While with terrestrial cases animal population declines are more associated with habitats being recruited for human use this is not the case with marine species. Over fishing has eliminated many species, at least commercially, the classic case is the North Atlantic cod. Cod populations where reduced to a level where its habitat was taken over by other species and even after 20 years has never shown that it is capable of returning to anything like a commercial entity let alone its former population. Scientists warned for many years of this possible outcome but politics and jobs were deemed more important (where have I heard that before?) in the end everyone lost out and the jobs disappeared presumably for ever. So humans have great trouble reaching reasonable predator/prey relationships and as with fisheries tend to move down the food chain and take out new species regardless of what has happened to the old.
The bottom line however is that even predators cannot be complacent it is just as likely that the unwary or infirm will end up as the prey as will any of the seemingly more likely candidates
DAVID BUTCHER