Small animals and vegetation structure

By Landcare Support Officer Wendy Gleen

An earlier article considered how vegetation structure – the arrangement of plants and their parts -affects a local kangaroo population. It is even more important for small animals, being crucial for their survival and shaping their whole life.

Several years ago I undertook a masters by research project looking at how small mammals respond to urban edge effects. To gain a rats-eye view of the bush and its hidden pathways, I attached a miniature cotton reel backpack to some native bush rats, tied the loose end of the cotton to a tree, and released them. The ultra- fine thread would catch on the vegetation as they moved along, preserving their path for me to come and trace the following day. All rats got a peanut butter ball in payment, the backpacks detached during the first 12 hours and no animals were harmed.

Above: Bogul (native bush rat) Rattus fuscipes Photo credit Wendy Gleen, Taronga Zoo.

It was fascinating to follow their trail, the thread was a criss-crossed tangle underneath dense vegetation, indicating they spent more time there, but it followed straight lines across open spaces, where they darted across.

This and some other work gave us a peek at how animals constantly juggle sophisticated cost/benefit decisions to balance three basic life requirements – safety from predators, obtaining food and avoiding fatigue (energy use). The structure of vegetation in an animal’s home range affects all of these factors; the way they move, shelter and forage, and decisions are crucial: there may be a juicy patch of berries ahead, but to get to it you have to cross an open space. Is exposure to predators too risky? Or maybe it’ s actually safer in the open patch where you can see predators approaching?

Ecological theories around habitat use ultimately inform best practise in bush regeneration techniques – it’s important to consider how weeds and their removal affect local fauna.

For example, at Dorrington Rathmines the weed honeysuckle forms a low mat -like structure of tangled stems which would impede travel by small mammals like bush rats (Fig 1). Compare the structural complexity of a healthy native patch just two metres away (Fig 2) which small mammals can hide under or travel through. As well as improving flora diversity, the local Landcare group is improving habitat for fauna as they tackle this weed infestation.

References and further reading
Bennett, A. F. “Microhabitat use by the long-nosed potoroo, Potorous tridactylus, and other small mammals in remnant forest vegetation, south-western Victoria.” Wildlife Research 20.3 (1993): 267-285.
Charnov, Eric L. “Optimal foraging, the marginal value theorem.” Theoretical population biology 9.2 (1976): 129-136.
Gleen, Wendy. “Life on the edge: Population and behavioural responses of the native bush rat to invasive species at the urban edge.” Master’s thesis, University of Sydney, 2013.