Wendy J. King

A capture technique for free-ranging eastern grey kangaroos (Macropus giganteus) habituated to humans

Available methods to capture free-ranging kangaroos differ in ease of use, selectivity, risk of injury and suitability to specific environments. We describe a simple technique involving the syringe from a ‘jabstick’ attached to an extendable, aluminium pole. We also examine responses of eastern grey kangaroos (Macropus giganteus) to a range of doses of Zoletil®. We captured 307 eastern grey kangaroos that were habituated to humans in Victoria, Australia, from November 2007 to October 2009. We approached kangaroos on foot, and injected the hind limb muscle mass with the pole syringe extended up to 4.85 m. We used Zoletil® 100 at a dose rate of 4.1 ± 1.3 mg kg–1 (mean ± s.d., n = 274). Induction was rapid (4.3 ± 2.0 min, n = 185) and only weakly related to dose (r2 = 0.06). There was no clear relationship between age, sex or body condition and induction time. This pole syringe technique can be successfully and safely used wherever animals can be approached closely, regardless of body condition. The technique provides an effective means to immobilise habituated kangaroos for research and management.

Effects of litter size and population dynamics on juvenile and maternal survival in Columbian ground squirrels

(1) The relationships between litter size and juvenile and maternal survival were investigated for 9 years in a marked population of Columbian ground squirrels (Spermophilus columbianus Ord.) in south-western Alberta, Canada. (2) A population increase during the first 4 years was characterized by larger litter size, greater adult female body weight and greater survival than in the last 4 years, during which the population decreased. (3) During the increase phase, modal litter size at emergence from the natal burrow was four, and the number of juveniles surviving to the following spring increased with litter size. During the decrease, modal litter size was three, and juveniles in large litters experienced high mortality. (4) Maternal survival was independent of litter size during the increase phase, but declined for litters larger than three in the decrease phase. The fitness costs of different litter sizes seem to vary according to population dynamics, possibly as a result of changes in resource availability.

Mother–offspring distances reflect sex differences in fine-scale genetic structure of eastern grey kangaroos

Natal dispersal affects life history and population biology and causes gene flow. In mammals, dispersal is usually male-biased so that females tend to be philopatric and surrounded by matrilineal kin, which may lead to preferential associations among female kin. Here we combine genetic analyses and behavioral observations to investigate spatial genetic structure and sex-biased dispersal patterns in a high-density population of mammals showing fission–fusion group dynamics. We studied eastern grey kangaroos (Macropus giganteus) over 2 years at Wilsons Promontory National Park, Australia, and found weak fine-scale genetic structure among adult females in both years but no structure among adult males. Immature male kangaroos moved away from their mothers at 18–25 months of age, while immature females remained near their mothers until older. A higher proportion of male (34%) than female (6%) subadults and young adults were observed to disperse, although median distances of detected dispersals were similar for both sexes. Adult females had overlapping ranges that were far wider than the maximum extent of spatial genetic structure found. Female kangaroos, although weakly philopatric, mostly encounter nonrelatives in fission–fusion groups at high density, and therefore kinship is unlikely to strongly affect sociality.

Few sex effects in the ontogeny of mother-offspring relationships in eastern grey kangaroos

Social relationships established early in life can have effects on social structure and influence individual fitness. Eastern grey kangaroos, Macropus giganteus, nurse their young for at least 18 months, allowing for a strong bond to develop between mothers and young. Because most female kangaroos are philopatric, the mother-offspring relationship established during lactation could persist into adulthood, resulting in clusters of female kin. Strong social bonds, however, are based on affiliative behaviours and frequent interactions. In particular, one might not expect strong bonds among related individuals unless there are advantages to interacting with relatives compared to associating with unrelated conspecifics. We examined development of the mother-offspring relationship in eastern grey kangaroos from permanent emergence from the pouch to the time of weaning. We studied a high-density population at Wilsons Promontory National Park, Victoria, Australia. There were few differences in the behaviour of sons and daughters towards mothers. However, daughters foraged slightly closer than sons to their mothers and daughters were weaned approximately 2 months later than sons if the mother did not have a surviving large pouch young. Mothers associated more closely with their daughters than their sons when offspring were aged 10–29 months but neither sex associated closely with their mothers beyond 33 months of age. Mothers never intervened to defend their young from aggressive individuals and it was the offspring that maintained spatial proximity to their mothers. Kangaroo mothers had few interactions with their juvenile offspring other than nursing. Females may be philopatric and settle near close kin as adults but kangaroos appear to have few of those early affiliative interactions necessary for social bonds to develop.

Adoption in eastern grey kangaroos: a consequence of misdirected care?

Adoption is rare in animals and is usually attributed to kin selection. In a 6-year study of eastern grey kangaroos (Macropus giganteus), 11 of 326 juveniles were adopted. We detected eight adoptions by observing behavioural associations and nursing between marked mothers and young and three more by analysing the relatedness of mothers and young using microsatellite DNA. Four adoptions involved reciprocal switches and three were by mothers whose own pouch young were known to subsequently disappear. Adoptive mothers were not closely related to each other or to adoptees but adoptive mothers and young associated as closely as did biological pairs, as measured by half-weight indices. Switch mothers did not associate closely. Maternal age and body condition did not influence the likelihood of adoption but females were more likely to adopt in years with high densities of females with large pouch young. Adoption did not improve juvenile survival. We conclude that adoptions in this wild population were potentially costly and likely caused by misdirected care, suggesting that eastern grey kangaroos may have poorly developed mother-offspring recognition mechanisms.