Darting, chemical capture and relocating kangaroos – an imperfect science and the new DBCA procedures

Kangaroos are regularly retained on golf courses when they are developed or in native vegetation in new residential subdivisions. People like to see kangaroos in their environment, however, we often fail to appreciate that a small number of kangaroos on a golf course or in a subdivision that are provided with permanent fresh water, quality green grass and shade, and which have become habituated to human activity will rapidly increase in number. An increasing population of kangaroos has consequences.

On golf courses, adult males (and occasionally females) can confront golfers that come too close and they dig up greens. These kangaroos also leave their scats on greens which is an inconvenience to golfers. In residential areas, they can be found in parkland or areas of native vegetation. Because there are often limited predators in these situations and they often have access to a good food supply, their numbers can increase to the point that they exceed the carrying capacity of the area. As kangaroos have little road sense they are often involved in vehicle collisions in residential areas.

In residential subdivisions, the problem is exacerbated, by the local people providing water, and in some cases, food for the kangaroos.

So, what is the solution?

The issue is best prevented. When subdivisions and golf courses are planned, exclude the kangaroos at an early stage. They are generally easily moved into adjacent areas, when there is a native vegetation linkage to adjacent areas. This can easily be addressed in the environmental assessment process and approval conditions for a new estate or a golf course.

Where there exists native vegetation adjacent to or near an isolated population of kangaroos, then they can sometimes be ‘herded’ into the new area; but herding kangaroos is very difficult and often requires the construction of temporary fencing. The return pathway must also be permanently blocked, and no food or water should be provided to the kangaroos that have been moved out of an area, as this will encourage them to stay in that area and become dependent on the new food source.

How about permanent sterilization?

Permanent sterilization of males (i.e. vasectomy or castration) and long-term sterilization of females is another population reduction strategy. Tribe et al. (2014) reported on a successful program to implant a contraceptive in females and vasectomise or remove the testicles of males. This program reduced the number of pouch young to about one half of pre-intervention levels and controlled the population levels over a 2-4 year period (a reduction in the birth rate from 0.3 to 0.06%/year for 16 months was achieved). Other studies have reported a female contraceptive implant which is effective for 7-8 years (Hynes et al. 2007, Hynes et al. 2010), and the sterilisation of males is permanent. The proportion of adult kangaroos surgically treated directly influences the subsequent population size. As best we can ascertain levonorgestrel, the contraceptive used by Hynes et al., (2010) has not be used on Western Grey Kangaroos, but was successfully used on Tammar Wallabies , so there is no reason why it should not be successful with the larger Western Australian Western Grey Kangaroo. Wilson and Coulson (2016) reported on a study where 65 adult female kangaroos were captured on a golf course in Anglesea, Victoria and some given levonorgestrel (210mg, n = 18) and deslorelin (9.4mg, n = 24) implants and there was a control group of 23. In normal years, less than 20% of females failed to reproduce. For deslorelin treated females, the odds of failing to reproduce were four times higher than for the control group; for levonorgestrel-treated females, these odds were 74 times higher. Deslorelin was ineffective after 3 years, whereas levonorgestrel was effective for at least 5 years.

Given that the testicles of males hang in a scrotum that hangs from the lower abdomen, vasectomy or castration would be relatively easy by a skilled veterinarian.

The drawback of sterilization is the cost. Permanent sterilization of males (i.e. vasectomy or castration) and long-term sterilization of females is expensive, and to provide long term control, almost the entire population would need to be sterilized.

Darting and chemical sedation of kangaroos is an imperfect science!

Darting, chemical sedation and relocating kangaroos is the option that is most often used, but it is not without its problems. Kangaroos are prone to capture myopathy – Capture myopathy or exertional rhabdomyolysis or stress myopathy occurs when muscle damage results from extreme exertion, struggling or stress resulting in a rapid increase in lactic acid in the muscles, which if not cleared leads to acidosis, a drop in the body fluid pH, heart failure and the muscle deterioration. Dying muscles release myoglobin, which can damage the kidney and lungs. The following four categories of capture myopathy are reported:

• death in minutes due to a release of potassium from damaged muscles causing heart failure;
• death in 24 to 48 hours, caused by staggering and muscle rupture;
• muscle and kidney damage, and where the animal is often seen lying in an awkward position. Death often occurs after a couple of days; and
• death occurs days or even months after the event and is often due to a heart attack.

Capture myopathy can be minimised by reducing the stress level, which in most cases relates to the length of exposure to a stressful situation. Fast, efficient and practiced procedures and an appreciation of what causes stress in kangaroos are the best defence against capture myopathy.

The drug typically used to dart and sedate kangaroos is Zoletil (a proprietary mixture of tiletamine and zolazepam). Zoletil is used because it has a wide margin of safety, requires only a small dose volume and is relatively quick acting for a range of mammals. The primary problem with Zoletil is the highly variable recovery time. For example, Mayberry et al. (2014) reported that with an intramuscular injection of 4.55 (± 0.98) mg kg-1 of Zotelil, 26 Western Grey Kangaroos recovery times varied from just over 1 hour to 3 hours (Figure 1, taken from Mayberry et al. 2014).

Figure 1. Time to recovery (h) for 24 adult female kangaroos sedated multiple times (first occasion [?], subsequent occasions [?]), and two young male kangaroos (one occasion each [?]), with varying dose rates (mg kg–1) of Zoletil® by intramuscular injection (R2 = 0.007, P = 0.86, df = 59).

We have had kangaroos take as long as 5-6 hours to stand and hop away after being sedated and relocated, while other kangaroos given a similar dose are mobile in 1.5hrs. Kangaroos that have been active before being darted, and that have an elevated metabolic and heart rates, respond very differently to a standard dose of Zoletil compared with ones that have been stationary eating grass when darted.

There are other issues. Once a kangaroo has been relocated, there is no guarantee it will survive. For example, we relocated kangaroos from a golf course to a bush site in the State forest east of Sawyers Valley. These kangaroos had been bred on the golf-course, had ready access to quality green grass and freshwater and were habituated to human activity. They were relocated to the State forest and required to find food, and if required, free water, shelter and to establish new social structures. The choice of the relocation site is determined by the Department of Biodiversity, Conservation and Attractions. Nobody knows how many of these kangaroos survived beyond 12 months of their relocation.

In rare occasions, when a dart hits a kangaroo, it fails to discharge the sedative into the kangaroo’s muscle. In this circumstance, there is kangaroo with a dart firmly embedded in its thigh muscle, trying to avoid all humans. Seldom is it possible to shoot these kangaroos because of where they are located, and it can be extremely difficult to get a second dart into these kangaroos and to remove the first dart.

Darts are propelled out of the dart gun by compressed air and it is always a judgement by the shooter as to how much compressed air to use, and this varies on how far you are from the target. Too little air pressure and the trajectory of the dart will be a significant loop and it is difficult to hit the target. Too much pressure results in a flatter trajectory, but the dart hits the kangaroo with force, and it almost certainly will rapidly hop away and will need to be found. The ideal scenario is a relatively flat trajectory, so only the needle of the dart enters the muscle and the kangaroo remains where it was shot, so that it is sedated on the spot. You get better with practice.

Video – click picture to download a kangaroo being darted to enable fauna relocation. It shows an initial response but then settles again.

What do you do with pouched joeys?

Stressed adult females will eject pouched joeys, preferring to survive themselves and have more joeys than protect a joey and perhaps not survive. What do you do with a joey that comes out of the pouch of a sedated and recumbent doe? In the sedated state the pouch often loses its capacity to hold the joey. Catching joeys is problematic, as they are often too small to successfully dart and sedate, too fast to catch and relocate with their mother, and even when they are caught and relocated with the mother, they will often hop away from their mother before she has fully recovered. They then become separated from their mother, and chances of survival are significantly reduced. Giving joeys to animal wildlife carers is also problematic. What happens to these joeys when they get older? Are they capable of surviving on their own without human assistance? There are no studies of the success or otherwise of joeys that have been raised by humans and subsequently released back into the wild to fend for themselves.

Standard operating procedure

The Department of Biodiversity, Conservation and Attractions (2017) has developed a SOP ‘Grey Kangaroo Relocation using Chemical Immobilisation Techniques’ that addresses many of these issues and provides guidance and direction on how some of these situations might best be handled. We are pleased to say that Terrestrial Ecosystems had input into the development of this guideline, so we agree with most of its content.

Monitoring relocated kangaroos

There is nothing in the literature on the survival success of darted, sedated and relocated kangaroos, or for that matter, kangaroos raised by animal wildlife carers and subsequently released into bushland to fend for themselves. There is an urgent need for this research. If kangaroos are being darted, sedated and relocated from golf courses and residential areas, only to die a slow death due to starvation or to be easily predated upon by foxes or wild dogs or to be killed on roads and tracks, then the more humane approach might be for them to be darted, sedated and euthanased in-situ.

References

Department of Biodiversity Conservation and Attractions. 2017. Grey Kangaroo Relocation using Chemical Immobilisation Techniques. Perth.

Hynes, E. F., K. A. Handasyde, G. Shaw, and M. B. Renfree. 2010. Levonorgestrel, not etonogestrrel, provides contraception in free-ranging koalas. Reproduction, Fertility and Development 22:913-919.

Hynes, E. F., C. D. Nave, G. Shaw, and M. B. Renfree. 2007. Effects of levonorgestrel on ovulation and oestrous behaviour in female tammar wallay. Reproduction, Fertility and Development 19:335-340.

Mayberry, C., R. Bencini, P. R. Mawson, and S. K. Maloney. 2014. Sedation of western grey kangaroos (Macropus fuliginosus ocydromus) with tiletamine-zolazepam. Animal Welfare 23:141-144.

Tribe, A., J. Hanger, I. McDonald, J. Loader, B. Nottidge, J. McKee, and C. Phillips. 2014. A Reproductive Management Program for an Urban Population of Eastern Grey Kangaroos (Macropus giganteus). Animals 4:562-582.

Wilson, M. E., and G. Coulson. 2016. Comparative efficacy of levonorgestrel and deslorelin contraceptive implants in free-ranging eastern grey kangaroos (Macropus giganteus). Wildlife Research. 43 (2) 212-219.

Photo – Kangaroos in a residential subdivision; Mum (sedated) and joey safely secured prior to relocation