07 June 2008

Mammals - An Overview

Australia's indigenous mammals without doubt have been the most severely impacted of all wildlife by European settlement and the predators they introduced. There are more locally extinct mammal species in the Esperance area, than the total number that survive today. The animals between the size of a rat and a small kangaroo have been the worst affected, becoming victims largely of the introduced fox. They were too large to effectively hide from them, but too small to move away.

According to old time locals, the fox arrived in the Esperance region along with the rabbit around or during the First World War. Up until that time the local native fauna had been reasonably intact, but those listed below have since become locally extinct, with some now only surviving on a few WA islands:

Brush-tailed Bettong - Bettongia penicillata (Australian Museum Records)
Burrowing Bettong - Bettongia lesueur (Australian Museum Records)
Banded Hare-wallaby - Lagostrophus fasciatus (Australian Museum Records)
Black-footed Rock-wallaby - Petrogale lateralis (Now only on south coast islands)
Tammar Wallaby - Macropus eugenii (from local knowledge)
Western Quoll - Dasyurus geoffroii (Australian Museum records)
Dibber - Parantechinus apicalis (Bones collected from cave, id by WA Museum)
Numbat - Myrmecobius fasciatus (Australian Museum Records)
Western Barred Bandicoot - Perameles bougainville (Australian Museum Records)
Bilby - Macrotis lagotis (Australian Museum Records)
Common Ringtailed Possum - Pseudocheirus peregrinus (Recorded by Eyre at Mt. Ragged)

Placental Mammals
Heath Rat - Pseudomys shortridgei
(Bones collected from cave, id by WA Museum)

Above are twelve indigenous mammal species that have gone locally extinct within the past 100 years. Predation by the fox is very likely the main cause, particularly of the larger species, but cats have also, and still do take a dreadful toll on the wildlife. Other contributing factors include land clearing, although large areas of bush still remain intact. Also inappropriate land management, ie the change from aboriginal fire management whereby a mosaic patchwork of burnt and unburnt vegetation is created that is required by many of the above animals. The aboriginal mosaic burns would have also reduced the frequency of large destructive wildfires, yet another destructive influence.

So a very poor environmental record for the Esperance and for that matter, the entire South Coast and hinterland region, which from my observations is not improving. However, relatively small areas that are being baited for foxes are reducing predator numbers and resulting in increased populations of native species. From my experience with fox baiting, it is a very short-term solution as their numbers are quickly replaced, so baiting must be regarded as an annual activity, not to be relaxed for a single season. A drawback though to fox eradication, is it permits cat numbers to increase, as they are much harder to bait and readily fill any predator gaps. These two predators to some degree tend to avoid each other, maybe this is due to competition for similar prey, or perhaps the fox targets the cat's kittens.

A major problem local mammal species have is suitable habitat in which to safely hide from these introduced predators. With the exception of the granite outcrops there are few environments with fallen logs and tree hollows to offer a retreat, as most trees in this district are small trunked and don't form sizeable hollows. The mallee further inland does have larger trees and some even have suitable hollows, but this environment is disadvantaged by the lack of regenerating fires that are so important for regeneration of small herbaceous flora, which in turn attract insects.

Suitable coastal limestone outcrops where animals can seek shelter are also limited by being few in number and small in size. So unless the animals can dig a deep hole, or find one of the few hollows in limestone or granite outcrops (currently not occupied by feral honey bees), they must nest on the ground to be eventually discovered by the numerous fox and cat predators.

I have not investigated marine mammals so offer no opinion regarding their welfare; the same applies to the microbats (Fruit-bats do not occur in southern WA). There are also several small mammals recorded for the district that I have not mentioned. These like the bats need to be trapped in order to locate and positively identify them, and as I am a private individual I lack the authority or the equipment to do so, so will not comment on them either. Even the small mammals I have encountered were more often a stroke of luck than any intention on my part. So unless you actually live in the area where these nocturnal animals occur, you are most unlikely to encounter them.

These small mammals are as follows:
MarsupialsCommon Dunnart - Sminthopsis murina
Fat-tailed Dunnart - Sminthopsis crassicaudata

Placental Mammals
Ash-grey Mouse - Pseudomys albocinerces
The non-native and feral placental mammals in this region I have personally encountered are as follows:

Black Rat - Rattus rattus (Common in suitable habitat, but generally sparse in bush areas).
House Mouse - Mus musculus (Common).
Rabbit - Oryctolagus cuniculus (Sparse in bush areas, preferring vegetated locations abutting cleared farming zones, but probably kept in check by feral cats and foxes).
Fox - Vulpes vulpes (Very common).
Feral Cats - Felis catus (Common).
Wild Horses - Equus caballus (Scattered small groups along coastal alkaline dunes west of Cape le Grand and around the mallee granite outcrops to the north and west of Mt. Ragged).
One-humped Camel - Camelus dromedarius (Scattered small groups in open mallee areas to the North and NW of Mt. Ragged).
Goats - Capra hircus (Not seen in the Esperance region, but common in the Goldfields).