Entanglements in conventional agricultural fencing pose a threat to wildlife. Although rescue and rehabilitation is possible in some cases, many animals that entangle themselves will perish. Of the ones discovered still alive, many will have sustained serious non-repairable injuries and must be euthanised. Others will be freed and die from latent complications such as die-back of tissue and internal damage.
In many observed cases the entangled animals have already expired, evidenced by partial remains of carcasses. These animals typically die from loss of blood, infection, starvation, heat-exhaustion, or increased vulnerability to predation. In some cases where electrification is used, small ground-travelling species such as echidnas, possums, and other reptiles become snared under the lowest wire and electrocuted to death.
Licensed wildlife-carers and rescuers have concerns about the entanglement of wildlife on barbed-wire fences. Due to the nature of the work involved in the rescue and rehabilitation of wildlife, these individuals are in legitimate positions to recognise notable threats to wildlife. In my own experience as an Emergency Phone Operator for Wildlife Victoria, I have received several calls regarding wildlife fence entanglements across the state. A system has been established to track all cases and provide statistics on wildlife injuries. Upon conducting a database search on fence entanglements, it was discovered that more than 250 reports were recorded in 2013 alone.
Agricultural fencing occurs in nearly all parts of Victoria and transcends most geographic areas and environments throughout the state. Per the Australian Natural Resources Atlas, agricultural activity occupies 61 percent (or 13.9 million hectares) of Victoria’s area. Of the 13.9 million hectares, nearly half (or 6.6 million hectares) is used for livestock grazing which utilizes the most problematic fencing designs. For example, the common six-wire configuration of single strand or ring-lock netting with a single or double top row of barbed-wire is one of the most problematic. Commonly used “off-the-shelf” prefabricated fencing configurations are also dangerous. The use of barbed-wire in the configuration, the close spacing of horizontal wires, and the netted configurations all threaten several species throughout the state. The economical Waratah “STOCKLOCK LONGLIFE 6/90/30”, used primarily for grazing livestock, is one instance of this.
In addition, Catchment Management Authorities (CMA’s) across the state utilize dangerous fencing configurations aimed at controlling livestock grazing and degradation in riparian areas. Although the intent is environmental conservation, these configurations have been observed to threaten species by restricting access to and from sources of water. Fences around water bodies such as wetlands and sewage ponds also pose entanglement threats. Large birds require extensive take-off and landing clearances and often have long legs that hang down during these manoeuvres. As an example, the West Gippsland Catchment Management Authority provides no mention of, or provisions for, safe fencing construction suited to indigenous wildlife in their “Fire Recovery Assistance for Native Vegetation Areas Application” guidelines. Moreover, studies have also indicated that feral animal exclusion fences threaten wildlife. The conservation value of these installations is noted, however, the lack of proper design and monitoring poses threats to wildlife in all areas across Victoria where these methods are employed.
Several physical characteristics of the environment are related to fence entanglements. Fences across flight and glide paths impact low flying species such as flying foxes and gliders. In marginal or cleared areas, glide distances are increased and species will land closer to the ground and strike fences as shown in Figure 1.0. Studies on the effects of fencing have determined that the entanglements involving barbed wire are common between cleared paddocks and vegetated roadsides. As animals forage for food or nest in vegetation, migration in and out places them at risk for entanglement, especially under stresses such as predator attacks.
Figure 1.0 – Photo Courtesy of Harry Kunz
In bush fires, restrictive fences pose an even greater threat by potentially entangling wildlife during a retreat from the fire zones. During these conditions, elevated numbers of species migrate away from the dangerous areas and fences of hazardous design impede movement thereby causing death by entanglement, asphyxiation, or incineration. Preliminary reports by the Victorian Association of Forest Industries estimate that millions of native animals were killed as a direct result of the 2009 bushfires. Many of these reported deaths were assumed to be per starvation and predation, two outcomes often associated with fence entanglements.
Vulnerable taxa that are threatened by fence entanglements include Pteropus poliocephalus (Grey-Headed Flying Foxes), Petaurus norfolcensi (Squirrel Gliders), and Grus rubicunda (Brolgas). Several other species including, but not limited to, Petaurus breviceps (Sugar Gliders), Petaurus australis (Yellow-bellied Gliders), Petauroides volans (Greater Gliders), Macropus giganteus (Eastern Grey Kangaroos), and Wallabia bicolor (Swamp Wallabies), Puffinus tenuirostris (Short-tailed Shearwaters) and various other birds have also been reported and documented as affected by the use of dangerous fencing. A study by Dr. Rodney van der Ree also reported several nationwide occurrences which are listed in Table 1.0.
Table 1.0 – Taken from van der Ree, 1999
In another case study conducted by Dr. Rodney van der Ree in the northern plains of Victoria, fifteen squirrel gliders were observed entangled in barbed-wire fences between 1994 and 1998. It should be noted that no systematic searching was undertaken and all observations were made from roadsides. Consequently, these figures may be grossly under-represented and actual entanglement occurrences could be much higher.
Most of the documented occurrences of Grey-Headed Flying Fox entanglements are from the State of Queensland. However, through personal interviews with trained rescuers and licensed shelter operators across the state of Victoria, it can be confirmed that the use of standard agricultural fencing causes fatal entanglements of bats.
Fence entanglement, as a legitimate threat to juvenile Brolgas, has been documented in various studies and action plans developed by the Victorian Department of Sustainability and Environment. Studies have demonstrated that fence hazards are increased for birds that travel long distances across water to take flight or that fly close to the water after taking flight.
Fence entanglements are often immediately fatal. Species suffer both direct and indirect impacts resulting from the collision with the fence. As an animal becomes ensnared in the fencing, it suffers multiple laceration wounds and severance to primary arteries. These injuries result in rapid blood loss and the subject dies from hypovolemia. This also occurs in cases where the subject has incurred a compound bone fracture as shown in Figure 2.0.
Figure 2.0 – Photo Courtesy of Wildlife Victoria Rescuer
In true flying species, such as bats and birds, entanglements cause severe damage to membranes and feathers as shown in Figure 3.0. Although initial injuries may not be directly debilitating to movement, continued struggle will increase entanglement and cause further injuries including hyperextension of bone structures and ruptured ligaments.
Figure 3.0 – Photo Courtesy of Sonja Elwood
Indirect impacts may include predation on the entangled animal. The animal becomes an effortless target for many feral species including red foxes, wild dogs, and wild cats and domestic species such as the common house cat and dog. These predators often rip the animal apart while it is still alive, due to suppressed defences from the fence entanglement. Remains are commonly found on fences suggesting death by predation as shown in Figure 4.0. Other indirect impacts include the orphaning of young when parent species are killed by fence entanglements.
Figure 4.0 – Photo Courtesy of Wildlife Victoria Rescuer
As mentioned previously, it is assumed that several more species are potentially affected by fence entanglements although not observed or formally reported. Many species in Victoria are nocturnal and may be entangled and predated upon during the night. Some research suggests fences constructed of barbed-wire and smooth metal wire are not easily seen or detected at night causing many animals to collide with the obstructions. Owls and other nocturnal birds are susceptible to this threat as shown in Figure 5.0.
Figure 5.0 – Photo Courtesy of Jenny Maclean
Barbed wire, causes entanglements in nearly all cases but is particularly dangerous to birds and bats. Bats may mistake the barbs for insects and fly into the fence during nocturnal hunting periods. Research has concluded that many species of bats forage at heights that bring them into contact with barbed-wire fences. Birds, on the other hand, may collide with fences when wires are not visible. This occurs when fence elements are concealed by vegetation, while birds are distracted such as during predation attacks or active chases during courtship, or during night or low light conditions. The barbs on the wires often snare wings or legs and birds are unable to free themselves.
Closely spaced wires in fencing (8 cm to 30 cm) create increased risks to ground-traveling species such as macropods and other marsupial mammals. Netted or “ring-lock” configurations seem to be the most problematic, causing severe entanglements and entrapments. Animals attempting to jump fences catch limbs in fence cells and with little flexibility in the crossed-wire configuration, are subject to horrendous injuries, such as compound fractures shown in Figure 2.0. Smaller species such as Koalas are entrapped when attempting to climb through the netting as shown in Figure 6.0.
Figure 6.0 – Photo Courtesy of Peter Black
Electrified fence wires located close to the ground (less than 200 cm) are fatal to echidnas, bandicoots, goannas, and penguins. The animal travels beneath the lowest wire and receives an electric shock. A wire that is placed too low will cause the animal to continue forward in an attempt to escape and become more lodged between the ground and the wire. As more electric current is delivered to the subject, it suffers cardiac arrest and perishes beneath the fence wire.
Finally, standard heights of most fences used throughout rural Victoria are between 90 and 110 cm. Many large macropods have the ability to completely clear fences at those heights, however, smaller macropods and females with joeys in pouch are not as fortunate as illustrated in figure 7.0. Under normal circumstances, the animal often miscalculates vertical clearances and strikes the top wires. In situations of duress, such as the threat of fire or predation, the animal is distracted and either misjudges or does not detect the true height of the fence.
Figure 7.0 – Photo Courtesy of Wildlife Victoria Rescuer