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eastern grey kangaroo (macropus giganteus)

predation  

A vigilant eastern grey

courtesy of The University of the Sunshine Coast

        Predators of the eastern grey kangaroo include dingoes, foxes, pythons, some large birds of prey, and humans (Dawson, 1995).  Dawson also notes that predators tend to focus on the young than on the adults.   As discussed earlier there are several strategies that the grey kangaroos use against predation.  First is their aggregations, another, their speed (that they usually use to go into semi-shallow bodies of water), and the third is how they flee sporadically as a group.  The manner in which kangaroos flee sporadically (in their direction and speed) can also serve to confuse a predator.  Another behavior (which might be considered selfish) is a type of signaling that these kangaroos use to warn against predators.  When in danger, kangaroos will beat on the ground with their hind feet. This alarm signal is loud and carries over a long distance (San Francisco Zoo Website).  Once again, it can serve to create confusion or to let a predator know that they are aware of its presence. 

       Reproductive females were found to be significantly more vigilant than other individuals in mobs (Colagross & Cockburn, 1993).  Females in flight are hindered by the pouch (Frith & Calaby, 1969).  As such, they have been known to remove their young and hide them while they flee.  As noble as this action sounds, Frith and Calaby argue that it is more likely that the mother engages in this behavior for selfish reasons.  She needs to lighten her own load so that she can increase her chances of survival.  This behavior is known as jettisoning and can occur at high speeds when the mother suddenly relaxes her pouch and the fall out.  Since the joey bolts rapidly in a random direction the chances of separation are very high.  According to Frith and Calaby these young are rarely adopted by other females and, as such, are likely to die. 

     A study by Clarke, Jones and Jarman concluded that these particular macropods are found in smaller groups at night.  The researchers based their study on pre-existing data that studies that showed this tendency and produced the same findings.  They reasoned that there must be an adaptive reason for a reduction in group size at night.  One reason for having this inkling is that the reduction in size took place at dusk, before it was totally dark, and was not a result of a sporadic loss of contact at night (Clarke, Jones & Jarman, 1995).  It is suggested that the nocturnal setting reduces the effectiveness of communication especially among larger groups.  Another possible reason relates to predation pressure.  Because the kangaroos rely on "many eyes" during the day to spot their predators, they have to switch up their strategy at night.  Predators rely more on auditory and olfactory cues at night and so a larger group size would not be advantageous to the kangaroos.  Ultimately, this data points to the high level of flexibility that is enjoyed by the eastern grey kangaroo.  The researchers suggest that this flexibility may be important for species that are highly dimorphic and in which males and females have differing energy requirements and predation pressure (Clarke, Jones & Jarman, 1995).

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