Monday, October 10, 2016

The Great Circle of Life and All That Jazz

So on this blog there are likely a whole library’s worth of hyena post archives, and rightfully so given the masthead of this entity, however with much less frequency do we discuss all of the events and states circling around this species that contextualize their existence.  Often times this conglomeration of events and states is culturally and romantically referred to as the circle of life.  In reality, it is less of a circle and more of the contemporary model of the atom with several orbiting electron shells influencing the nucleus where biotic interactions play themselves out.  The influences of these electron shells might include, but are not limited to: the movement of tectonic plates, lunar tidal forcing, the hydrologic cycle, long-term climatic trends, random destructive events like volcanic eruptions or tsunamis, and anthropogenic impacts.  To keep things simple, let’s acknowledge the existence of these electron shells but consider only biotic nucleus of interactions that our hyenas encounter on an annual basis. 

Mufasa teaches Simba the meaning of the Great Circle of Life.

Although hyenas are often given a bad rap as the bully scavengers of the African savannah, in the Mara [Overused Statistic Warning!], hyenas hunt up to 90% of their own food due to the abundance of prey species.  Hyenas are also incredibly versatile predators.  They have been known to hassle hippos and baby elephants when in large numbers, hunt every species of ungulate that inhabits the Mara when the opportunity arises, and Fisi RAs have even seen them eating termites and harassing turtles.  It is even more impressive if you consider that each of these species has different adaptations to thwart predators and in spite of these hyenas can still successfully hunt them.  Hippos and elephants have great bulk and stamina, wildebeest and zebra use numbers and coat patterns for predator swamping, topi stand on termite mounds to spot predators, impala and Thomson’s gazelle rely on speed and agility, and turtles utilize their hard shells for protection.

Baby Thomson's gazelles make for superb fun-sized hyena snacks.
Moving on, hyenas do not only need to catch the prey they desire but also compete with other predators in the Mara ecosystem.  Lions (ambush pack hunters), leopards (solitary ambush predator), cheetahs (speed specialist), and African wild dogs (pack hunting endurance specialists) may have different modes for catching prey but their niches still overlap to a degree.  By hunting in groups, using great endurance, and bone-crushing jaws, the generalist hyena can persist in this matrix of apex predators.

A male lion kills an adult wildebeest after a sunset crossing of the Mara river. 
Once hyenas have successfully killed their prey animal of choice, they must defend it against scavengers looking to stake their claim on the carcass.  Lions are a perennial threat to hyena kills.  It requires four adult hyenas to fend off one lioness and seven adult hyenas to defend against one male lion, so unless there are a large number of hyenas on a carcass it is very easy for lions to bully hyenas off a kill.  While these animals cannot steal an entire carcass from a clan of hyenas, jackals, marabou storks, vultures, and mongoose will attempt to steal scraps if hyenas aren’t actively defending their kill.  Over time, this can sometimes significantly diminish the caloric value of the carcass.  When considering hyenas’ scavenging abilities, the aforementioned bone-crushing jaws certainly aid in giving these animals access to bone marrow – a resource that not too many other carnivores can readily access.

It's a good thing detritivores are always hard at work cleaning up dead things when scavengers remain uninterested, otherwise this bloated hippo carcass would be floating around for a while. 
Although hyenas are capable of consuming 20% of their body weight in a single sitting, decay still becomes an issue even after considering competitors and scavengers.  It is certainly a good thing that microbes break down dead plant and animal matter, but this also means that after a certain amount of time carcasses will no longer possess a dietary value to hyenas.  It certainly plays a role in how often hyenas hunt, how quickly they consume meat, how much they can eat, and which parts of the animal they eat.

This is one of the many beautiful flowers that grows in Maasai Mara, making it a great neighborhood to raise hyena cubs.

Numerous grass species dominate the Mara in places and their height can have a significant impact on visibility.  This impacts hyenas in more ways than one.  Obviously, it is a great boon to hunting as ungulates have a much harder time spotting potential predators.  However, tall grass can also obscure hyena kills from scavengers and dens from threats to their cubs.  Meanwhile, shade-providing shrubs and trees can create microclimates up to 30oF cooler than the surrounding environs.  This provides a nice, cool place to sack out in the middle of the day.

1 comment:

dee said...

I enjoyed reading your post. Keep up the good work.

Michigan State University | College of Natural Science