Individual study: Survival implications of removing young tammar wallabies Macro eugenii from pouches for short time-periods: effects of environmental temperature, South Australia
Taggart D.A., Shimmin G.E., Underwood G. & Phillips K. (2002) Survival of very small macropod pouch young following short-term isolation from the pouch at various environmental temperatures. Animal Conservation, 5, 275-282
Cross-fostering can be an important means of improving the breeding success of small groups of threatened species. A number of macropods (kangaroos, wallabies, tree kangaroos and pademelons) persist in small isolated groups or are threatened with extinction. To bolster populations and ensure greater genetic diversity, it may be necessary to introduce new genetic stock from the wild. It is thought that the introduction of pouch young into the population is a good method to achieve this, as introduced adult macropods often fail to reproduce. Little is known about carrying out the transfer of small pouch young into wild populations, but it would inevitably require their removal from the mother and transport. Here, the results of a study in which the effects of temperature on the survival of removed young tammar wallabies Macro eugenii are described.
Study site & wallaby maintenance: The tammar wallabies Macro eugenii used in the study were maintained in large outdoor enclosures (1-3 ha) in Tidbinballa Nature Reserve near Canberra, Australia. All wallabies had a access to a variety of native grasses and were fed supplements of fresh fruit, vegetables, oats and dietary pellets.
Removal & translocation of pouch young: Female wallabies were netted between February and July 1999 and those with small pouch young were selected and anaesthetized with Isoflurane, administered by a mask for about 15 minutes. Small young were selected because these are the primary targets when fostering threatened animals. In total young were selected from 24 individuals, comprising one control group of five individuals and three experimental groups (1-3) of eight, five and six individuals respectively. Pouch young were removed and then weighed, aged and sexed. Full biometric measurements and a number of observational data were recorded.
Incubation & reattachment: Wallaby pouch young were kept in a portable incubator for six hours. This period represents the maximum time to transport a pouch young from the wild into captivity and attach it to the teat of a waiting foster mother. Temperature was maintained at 30°C for experimental group 1, 27°C for group 2 and 23°C for group 3. Relative humidity was maintained at 100% at all times by placing a container of water in the incubator.
At the end of the 6-hour isolation period, individuals were removed from the incubator, reweighed and their body condition noted. They were then physically reattached to the mother's teat using fine, blunt-nosed forceps. Reattachment took 1-2 minutes to complete. The control group was removed, weighed etc. and then reattached immediately. Mothers were then recaptured one week later and again at three months post isolation to check survival of young.
Survival & body conditions: All young in the control group survived. Better survival and lower weight loss were maintained in experimental groups when incubation temperatures were lower. The effects of incubation temperature on percentage weight loss and survival are shown in Table 1 (attached). The percentage weight loss in group 3 was statistically significantly lower that that of groups 1 and 2. The percentage body weight loss in experimental groups 1 and 2 were affected by both the size and age of the pouch young, being greater as size and age decreased. The effects were most marked in group 1. For group 3, size and age did not affect weight loss. All individuals surviving after one week were alive three months after isolation.
Conclusions: The trials suggest that it should be possible to isolate very small pouch young of tammar wallabies without compromising their health or survival, provided that high humidity and low temperatures are maintained. The use of this procedure in combination with cross fostering techniques could allow small pouch young from threatened macropod species to be recruited directly from the wild into captivity, for captive breeding or to improve genetic diversity in captive colonies.
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