Female Eastern Grey Kangaroos Research Articles

Higher sociability leads to lower reproductive success in female kangaroos.

In social mammals, social integration is generally assumed to improve females' reproductive success. Most species demonstrating this relationship exhibit complex forms of social bonds and interactions. However, female eastern grey kangaroos (Macropus giganteus) exhibit differentiated social relationships, yet do not appear to cooperate directly. It is unclear what the fitness consequences of such sociability could be in species that do not exhibit obvious forms of cooperation. Using 4 years of life history, spatial and social data from a wild population of approximately 200 individually recognizable female eastern grey kangaroos, we tested whether higher levels of sociability are associated with greater reproductive success. Contrary to expectations, we found that the size of a female's social network, her numbers of preferential associations with other females and her group sizes all negatively influenced her reproductive success. These factors influenced the survival of dependent young that had left the pouch rather than those that were still in the pouch. We also show that primiparous females (first-time breeders) were less likely to have surviving young. Our findings suggest that social bonds are not always beneficial for reproductive success in group-living species, and that female kangaroos may experience trade-offs between successfully rearing young and maintaining affiliative relationships.

Laparoscopic ovariectomy in eastern grey kangaroos (Macropus giganteus) and red kangaroos (Macropus rufus).

To develop a technique for permanent sterilisation of female eastern grey kangaroos (Macropus giganteus) and red kangaroos (M. rufus) as part of a large-scale macropod management program on an enclosed 1545-ha site in western Sydney. Free-ranging female kangaroos (n = 1409: 1285 eastern grey kangaroos, 124 red kangaroos) were anaesthetised via remote anaesthetic drug delivery of tiletamine/zolazepam, medetomidine and acepromazine prior to inhalational anaesthesia using isoflurane-oxygen. A laparoscopic ovariectomy technique was developed using standard laparoscopic equipment to effect permanent sterilisation of the kangaroos. The technique described was also adapted for use on immature animals weighing as little as 1 kg. No direct post-surgical care was provided once the animals had recovered from the anaesthetic. The procedure was simple to perform and had a very high success rate, with an overall project mortality rate of 2.13% (n = 30). Seven kangaroos (0.05% of all operated kangaroos) were euthanased as a direct result of the surgical procedure. Surgical complications were rare but included inadvertent gastrointestinal tract puncture with the trocar, intraoperative haemorrhage and subcutaneous emphysema leading to pouch eversion following surgery. The procedure described is a rapid and effective method of permanent fertility control in macropods and carries a low mortality rate.

Food supply fluctuations constrain group sizes of kangaroos and in turn shape their vigilance and feeding strategies

Seasonal variation in food resources and predation risk imposes major constraints on herbivores, which must adjust their behaviour to maximize their energy intake and survival. In seasonally driven landscapes, it is not yet clear what the primary drivers are that shape seasonal variation in vigilance and feeding rates. These rates have been shown to vary in relation to various environmental, social and individual factors, but many of these factors also vary through the year, due to variation in food supply. We studied wild female eastern grey kangaroos, Macropus giganteus, under low predation risk over a year to investigate whether vigilance and feeding rates varied seasonally and whether this variation was mainly driven by food quantity or quality, group size or individuals' reproductive states. Both vigilance and feeding rates varied seasonally, as did food quantity and quality and group size. Vigilance, including antipredator (head orientation away from the group) and exclusive (i.e. vigilance without chewing) vigilance, decreased and feeding rate increased with increasing group size. However, because group size increased with food quality and quantity, food resources emerged as the primary driver of variation in behavioural strategies. These results suggest that the observed effects of group size on the trade-off between food acquisition and safety are in fact corollaries of the seasonal variation in food supply in our study system, in which the risk of predation on adults is low, and hence are by-products of the foraging choices made by kangaroos in response to the dynamics of the quantity and quality of food.

Tall young females get ahead: size-specific fecundity in wild kangaroos suggests a steep trade-off with growth.

When resources are limited, organisms face allocation conflicts. Indeterminate growth creates a persistent conflict with reproduction, as growth may enhance future reproduction, but diverts resources from current reproduction. Little is known about allocation trade-offs in mammals with indeterminate growth. We studied growth and reproduction in adult female eastern grey kangaroos (Macropus giganteus), an iteroparous mammal with indeterminate growth. Allocation trajectories varied with age and size: for 4-year-old females, fecundity increased from 30 to 82% from shortest to average-sized individuals. Older females had high fecundity regardless of size. The smallest females grew 30% more annually than average-sized females, but females that reached average size at an older age had lower growth rates. Environmental conditions affected allocation to size and reproduction. Rainy springs increased fecundity from 61 to 84% for females that had previously reproduced, but rainy winters reduced leg growth. Females in better relative condition grew 40% more than average, whereas most young of females below average relative condition failed to survive to 10months of age. These results highlight an age-specific trade-off between growth and reproduction. Tall young females benefit from a smaller trade-off between somatic growth and early fecundity than shorter females of the same age, but older females appear to favor reproduction over growth regardless of size. Our study highlights how individual heterogeneity determines trade-offs between life-history components. We speculate that cohort effects affect age-specific reproductive success in this long-lived mammal.

Predators, food and social context shape the types of vigilance exhibited by kangaroos

Vigilance in prey species can serve many purposes, including predator detection and monitoring other group members, and is generally thought to impose a cost due to reduced food intake. However, previous studies have shown that herbivores are able to reduce the foraging cost of vigilance by chewing their food during vigilance bouts (‘vigilance with chewing’, as compared to ‘vigilance without chewing’). How predation risk, food availability and competition affect both the functions and the foraging costs of vigilance remains an open question. We studied female eastern grey kangaroos, Macropus giganteus, during winter and summer, when available food supplies were poor and rich, respectively, to investigate how group size, distance to cover, proximity between foragers and food patch quality affected decisions of foraging female kangaroos to exhibit antipredator or social vigilance, distinguishing vigilance with and without chewing. The use of antipredator vigilance was mainly driven by the perception of predation risk, and antipredator vigilance without chewing decreased with increased group size whereas antipredator vigilance with chewing increased nonlinearly with group size in winter. Distance to cover affected both forms of antipredator vigilance in summer only but there was no effect of nearest-neighbour distance. Social vigilance was affected positively by group size, and distance between foragers affected social vigilance without chewing positively, particularly in winter, and social vigilance with chewing negatively. Finally, patch quality increased the use of social vigilance with chewing in both seasons and decreased the use of antipredator vigilance with chewing in winter. This study provides new information on how animals make decisions about the functions and foraging costs of vigilance and allows a better understanding of how social foragers respond to an ever-changing environment.

Experimental manipulation of female reproduction demonstrates its fitness costs in kangaroos.

When resources are scarce, female mammals should face a trade-off between lactation and other life-history traits such as growth, survival and subsequent reproduction. Kangaroos are ideal to test predictions about reproductive costs because they may simultaneously lactate and carry a young, and have indeterminate growth and a long breeding season. An earlier study in three of our five study populations prevented female eastern grey kangaroos (Macropus giganteus) from reproducing during one reproductive season by either inserting contraceptive implants or removing very small pouch young. We explored how individual and environmental variables affect the costs of reproduction over time, combining this experimental reduction of reproductive effort with multi-year monitoring of 270 marked females. Experimental manipulation should control for individual heterogeneity, revealing the costs of reproduction and their likely sources. We also examined the fitness consequences of reproductive effort and offspring sex among unmanipulated individuals to test whether sex allocation strategies affected trade-offs. Costs of reproduction included longer inter-birth intervals and lower probability of producing a young that survived to 7months in the subsequent reproductive event. Weaning success, however, did not differ significantly between manipulated and control females. By reducing reproductive effort, manipulation appeared to increase individual condition and subsequent reproductive success. Effects of offspring sex upon subsequent reproductive success varied according to year and study population. Mothers of sons were generally more likely to have a young that survived to 7months, compared to mothers of daughters. The fitness costs of reproduction arise from constraints in both acquisition and allocation of resources. To meet these costs, females delay subsequent parturition and may manipulate offspring sex. Reproductive tactics thus vary according to the amount of resource available to each individual, promoting a wide range in reproductive performance within and among individuals and populations.

Within-population differences in personality and plasticity in the trade-off between vigilance and foraging in kangaroos

Behavioural traits can vary between individuals from the same population. These differences can involve consistent variation in the level of a particular behaviour (personality) or differences in the way individuals adjust their behaviour to environmental gradients (plasticity). In prey species, feeding rates and vigilance vary with environmental, social and individual factors and the feeding rate/vigilance relationship reflects the trade-off between food acquisition and safety. While feeding rates and vigilance have been shown to vary between individuals in relation to group size and predation risk, how they relate to other factors has not yet been investigated, nor has between-individual variation in this tradeoff. We studied between-individual variation in vigilance, feeding rates and their trade-off in female eastern grey kangaroos, Macropus giganteus, to see whether females showed consistent behavioural differences and different plasticity in relation to ecological (food patch richness), social (group sizes) and physiological (reproductive states) conditions. We addressed two contrasting hypotheses: an ‘ecological’ hypothesis under which individuals facing the same conditions should behave similarly, and a ‘behavioural’ hypothesis under which they should behave differently because of their own personality or plasticity. Female kangaroos tended to adjust their behaviours similarly in relation to ecological and social conditions, supporting the ecological hypothesis. However, they also showed differences in personality and plasticity in relation to their reproductive states that could not be explained by energetic demand alone; this was suggestive of different maternal strategies, thus supporting the behavioural hypothesis. Altogether these results suggest that consistent differences in animals’ personality and behavioural plasticity can be promoted by physiological conditions and are not necessarily repeatable across different ecological contexts.

Associations are more strongly correlated with space use than kinship in female eastern grey kangaroos

Understanding the relationship between kinship and female social preferences in mammalian societies is frequently complicated by philopatric behaviour and variation in pairwise home range overlap. While the influence of space use on association patterns is increasingly being considered in studies using network analysis, methods are needed for generating null models that control for pairwise home range overlap. We investigated female associations in a wild population of eastern grey kangaroos, Macropus giganteus, a species with higher fission-fusion dynamics, to test the influences of home range overlap and kinship on pairwise association strengths. Genetic analysis revealed that females were highly philopatric and we found that association strengths were significantly correlated with home range overlap. To test for social preferences, we compared observed associations with random associations based on individuals' space use, simulated using Digiroo2. HWIG, a version of the half-weight association index that controls for among-individual variation in gregariousness was used for all analyses. Preferred associates had significantly higher pairwise relatedness than expected. Although some females had strong social relationships with some of their close kin, in general, space use had a much stronger correlation with association strengths than both pairwise relatedness and maternal lineage. This suggests that familiarity may play a key role in driving association patterns in female kangaroos. We recommend controlling for individuals' space use when undertaking studies on social preferences and social structure in general.

Social preference influences female community structure in a population of wild eastern grey kangaroos

Communities, clusters of individuals who interact socially primarily with each other, are fundamental elements of social structure in many species. Community membership can be influenced by spatial factors and by social preferences resulting from genetic or phenotypic assortment or shared behavioural strategies. Very little is known about community social structure in herbivorous mammals with higher fission–fusion dynamics, which are societies in which group membership frequently changes. Using network analysis on data from 171 wild female eastern grey kangaroos, Macropus giganteus, a species exhibiting these foraging and social attributes, we quantified the presence of significant, strong community structure. Lagged association rates confirmed the temporal stability of this intermediate-level social tier. Communities' home ranges overlapped considerably, but their core home ranges were more dispersed, suggesting some influence of spatial factors on community membership. However, community-level social assortment was maintained in areas in which core home ranges overlapped, even though communities used these areas simultaneously, implying that social preferences also influence the presence of communities in female kangaroos. Within-community pairwise relatedness levels based on microsatellite markers were somewhat higher than those across the population, probably because of philopatry, but mitochondrial DNA revealed that communities did not reflect matrilines. This study contributes to the growing literature attempting to understand the factors driving fission–fusion social dynamics by showing that extensive home range overlap among communities can occur in the absence of behaviours usually associated with the maintenance of social preferences.

Offspring sex, current and previous reproduction affect feeding behaviour in wild eastern grey kangaroos

In mammals, lactation is the most energetically demanding component of female reproduction. Theory predicts an increase in food intake by lactating females, but very few studies have used contraceptives to experimentally test the influence of reproduction on foraging behaviour of wild mammals. From 2009 to 2011, we observed 182 individually marked female eastern grey kangaroos, Macropus giganteus, in two populations, including 29 that received an experimental contraceptive treatment. We sought to determine whether lactating females increase their foraging rate compared to contracepted and naturally nonlactating females. The proportion of time spent foraging during 10 min focal samples did not vary according to reproductive status in one population. In the other, lactating females spent 4% less time feeding than nonlactating females. Day and midday activity and bite and chewing rates were higher in lactating than in nonlactating females. Bite rate increased with the size of the pouch young and was higher for mothers of sons than for mothers of daughters. Bite rate was also affected by reproductive effort in the previous year, being higher for females that had weaned a young. Foraging behaviour was independent of body mass and group size, but bite rate appeared to decrease with female age. In one population, we found strong effects of date and year on foraging behaviour. Our study is a rare experimental manipulation of reproduction in free-ranging large mammals. We found that foraging behaviours were affected by both previous and current reproductive effort and varied with individual characteristics and environmental conditions.

Individual traits influence vigilance in wild female eastern grey kangaroos

Vigilance is an essential component of antipredator behaviour and is also used to monitor conspecifics, but is traded off against feeding in herbivores. This trade-off can be influenced by variation in many environmental, social and individual traits. Our aim was to test the relationship between individual-level traits, including boldness, body condition and reproductive state, and vigilance, while controlling for environmental and social variables. Using multiple 5-min video samples of 30 foraging, individually recognisable, female eastern grey kangaroos (Macropus giganteus) at Sundown National Park in Queensland, we investigated individual-level variation in the duration, intensity and target of vigilance behaviour during foraging. On separate occasions, we used flight-initiation distance tests to measure boldness in our kangaroos. Females with longer flight-initiation distances (shyer females) spent more time vigilant, providing preliminary support for studies of animal personality that have suggested that boldness may covary with vigilance. Body condition did not affect the total time spent vigilant, but females in poorer body condition spent more of their vigilance time in low-intensity vigilance. Vigilance patterns were not related to reproductive state, but varied among months and differed between mornings and afternoons, and females spent more time in high-intensity vigilance when further from cover. Even after accounting for all our variables we found that 7% of the variation in total time vigilant and 14% of the variation in vigilance intensity was explained by individual identity. This highlights the importance of individual-level variation in vigilance behaviour.

Individual variation in vigilance in female eastern grey kangaroos

For herbivores, vigilance usually involves a trade-off with foraging, and a further trade-off between antipredator and social vigilance. Thus individual variation in vigilance may result in significant fitness consequences. We used mixed-effects models to document individual variation in vigilance in wild adult female eastern grey kangaroos (Macropus giganteus) in Queensland, Australia. We tested the effects of group size, presence of adult males and wind on vigilance patterns and variation by analysing 399 five-minute samples on 31 individually identified females who were foraging on the periphery of groups. We determined the proportion of time that individuals spent vigilant, and the proportions of vigilance time spent in social versus antipredator vigilance and in low- versus high-intensity vigilance postures. The proportion of time females spent vigilant decreased with increasing group size but was not affected by wind speed or male presence, while the amount of their vigilance time spent in social vigilance was affected by interactions among the variables. After controlling for these effects, 13 females’ vigilance patterns were significantly different from the population mean. Individual variation was also found in vigilance postures used and the effect of male presence. Understanding individual variation in vigilance is important for understanding individuals’ antipredator and social strategies.

Deslorelin implants in free-ranging female eastern grey kangaroos (Macropus giganteus): mechanism of action and contraceptive efficacy

Context Fertility control offers a non-lethal management technique for iconic yet overabundant wildlife. Slow-release hormonal implants containing deslorelin show promise for managing free-ranging populations, particularly in peri-urban reserves, but most studies have been limited to captivity. Aims We investigated the efficacy and mechanism of deslorelin implants in free-ranging female eastern grey kangaroos (Macropus giganteus) under realistic management conditions. Methods We assigned females to a deslorelin (9.4 mg, n = 53) or placebo (n = 56) group at three peri-urban sites in Victoria, Australia, and monitored reproductive success for 3 years by observing young in the pouch. We tested the plasma LH response of control and treated females to exogenous GnRH, and compared the size of ovarian follicles between the two groups. Key results Deslorelin implants reduced fertility at all three sites. No deslorelin-treated females bred in Year 1 at Anglesea and Serendip versus 42% and 44% of control females respectively. At Plenty Gorge, 60% of deslorelin-treated females bred in Year 1 versus 100% of control females. In Year 2, between 11% and 39% of the treated females bred versus between 82% and 100% of control females at all sites. The contraceptive efficacy reduced by Year 3 when between 43% and 57% of the treated females bred versus between 85% and 100% of controls. A GnRH challenge elicited higher plasma LH concentrations in control than in treated females, and unlike untreated females, treated females lacked ovarian follicles >2 mm. Conclusions Deslorelin implants reduced fertility in free-ranging female eastern grey kangaroos over three successive breeding seasons. Chronic exposure to deslorelin desensitised the pituitary gland to GnRH and suppressed follicular development, but did not inhibit the development of a blastocyst, pregnancy or lactation in at least some females that had conceived before treatment. Implications Effective population management using deslorelin implants will require females to be re-treated on multiple occasions because the contraceptive effect lasts only a portion of their reproductive life. This would be practical only at sites where kangaroos are relatively easy to capture. The timing of treatment is also important in a species that undergoes embryonic diapause, particularly at sites providing high-quality habitat.

Investigating Differences in Vigilance Tactic Use within and between the Sexes in Eastern Grey Kangaroos

Aggregation is thought to enhance an animal’s security through effective predator detection and the dilution of risk. A decline in individual vigilance as group size increases is commonly reported in the literature and called the group size effect. However, to date, most of the research has only been directed toward examining whether this effect occurs at the population level. Few studies have explored the specific contributions of predator detection and risk dilution and the basis of individual differences in the use of vigilance tactics. We tested whether male and female (non-reproductive or with young) eastern grey kangaroos (Macropus giganteus) adopted different vigilance tactics when in mixed-sex groups and varied in their reliance on predator detection and/or risk dilution as group size changed. This species exhibits pronounced sexual dimorphism with females being much smaller than males, making them differentially vulnerable toward predators. We combined field observations with vigilance models describing the effects of detection and dilution on scanning rates as group size increased. We found that females with and without juveniles relied on predator detection and risk dilution, but the latter adjusted their vigilance to the proportion of females with juveniles within their group. Two models appeared to equally support the data for males suggesting that males, similarly to females, relied on predator detection and risk dilution but may also have adjusted their vigilance according to the proportion of mothers within their group. Differential vulnerability may cause sex differences in vigilance tactic use in this species. The presence of males within a group that do not, or only partially, contribute to predator detection and are less at risk may cause additional security costs to females. Our results call for reexamination of the classical view of the safety advantages of grouping to provide a more detailed functional interpretation of gregariousness.

Structured association patterns and their energetic benefits in female eastern grey kangaroos, Macropus giganteus

Little is known about the determinants of females' social interactions in species with fission–fusion social organization, in which individuals associate with different individuals at different times. Even less is known about social organization in marsupials. We investigated the association patterns of wild female eastern grey kangaroos in southeast Queensland. Female kangaroos had a nonrandom social structure and we present a new methodology for analysing social structure that accounts for the amount of spatial overlap shared by pairs of female kangaroos. This simulation model showed that patterns of association among our female kangaroos were not simply those predicted by their patterns of spatial overlap. Females that associated frequently with certain associates were able to graze for longer because they were less vigilant, and thus were able to benefit from having frequent associates. Female kangaroo social structure was affected by the loss of key members of the society during a period of unusually high predation. Information-theoretical modelling showed that the factors affecting grazing behaviour changed after partial population turnover, with the strength of association between nearest neighbours having a positive effect on grazing behaviour before population turnover and group size having a positive effect on grazing behaviour after population turnover. We propose that social organization within this marsupial is more structured than previously thought.

Fertility control in female eastern grey kangaroos using the GnRH agonist deslorelin. 1. Effects on reproduction

Eastern grey kangaroos are widespread on the east coast of Australia and frequently reach high densities in reserves and parkland near urban areas. Management of these populations is highly contentious and non-lethal fertility-control technologies are sought as an alternative option to manage population size. This study evaluated the potential of slow-release gonadotrophin-releasing hormone agonist (deslorelin) implants to inhibit reproduction in female kangaroos. Deslorelin treatment effectively inhibited reproduction in adult females for periods of 559 ± 111 days (n = 6) and 651 ± 21 days (n = 5) after administration of one or two 10-mg implants respectively. Animals treated with the lower dosage tended to resume breeding earlier than those that received a total of 20 mg of deslorelin (minimum duration of 18 months). Deslorelin treatment had no effect on blastocyst reactivation in a single treated female and repeat treatment had no negative side-effects. This study has demonstrated that slow-release deslorelin implants can successfully inhibit reproduction for extended periods in the female eastern grey kangaroos. This approach may have potential application in reproductive management of problem kangaroo populations.

Fertility control in female eastern grey kangaroos using the GnRH agonist deslorelin. 2. Effects on behaviour

In recent years fertility control has been proposed as an ethically acceptable alternative to lethal control techniques when managing overabundant kangaroo populations. A promising non-steroidal, non-immunological approach to contraception in female kangaroos involves the use of slow-release implants containing the gonadotrophin-releasing hormone (GnRH) agonist deslorelin. The practicality of using deslorelin implants as a management option is dependant on its effective inhibition of reproduction without negative physical or behavioural side-effects. This study investigated the behavioural effects of deslorelin implants in female eastern grey kangaroos. Treatment had no detectable effects on crepuscular activity. Alterations in the frequency of sexual interactions were observed in deslorelin-treated females, with a behavioural oestrus induced ~3 days after combined removal of pouch young and deslorelin administration. Copulation was observed during this early oestrous period, but conception was not achieved and pouch young were not observed in any treated females. Control females gave birth within 69.6 ± 10.4 days (mean ± s.e.m., n = 9) of placebo implant administration. The first births observed in treated animals were on Days 510, 637 and 643 after treatment. The remaining seven treated animals had not bred by the end of the study, a period of 647 days.

Fertility Control in the Eastern Grey Kangaroo Using Levonorgestrel Implants

We investigated the effect of subcutaneous levonorgestrel implants on reproduction, gestation, lactation, and body condition in both captive and free-ranging populations of female eastern grey kangaroos (Macropus giganteus). Kangaroos had their pouch young removed and were given either 2 control (inert) or 2 levonorgestrel implants. During January 1999, 3 kangaroos in the captive population received control and 3 received levonorgestrel implants. All of the control-treated females had given birth 3 months after treatment. None of the levonorgestrel-treated females gave birth during the investigation (25 months). In the free-ranging population, 8 females received control and 18 received levonorgestrel implants. Seven of the controls and 3 of the levonorgestrel-treated females gave birth during the first year. The 3 levonorgestrel-treated females that reproduced confirmed that levonorgestrel does not affect the reactivation or subsequent development of a blastocyst in diapause and that it has no effect on parturition. All 3 pouch young were successfully reared to weaning, demonstrating that levonorgestrel treatment does not affect the establishment or maintenance of lactation. All of the control-treated females gave birth to new young during the second year, whereas none of the levonorgestrel-treated females reproduced. Mean body weight of the levonorgestrel-treated females increased by 13.8%, significantly more than the 1.2% increase in control-treated females. However, a comparison of leg and foot length versus weight change identified 4 young females in the levonorgestrel-treatment group that underwent considerable somatic growth during the investigation. When these females were removed from the treatment group, no significant difference occurred between the 2 groups. Therefore, levonorgestrel had no adverse effect on body condition in the kangaroos. Levonorgestrel implants provide a safe, highly effective, and long-term (at least 27 months) method of contraception for eastern grey kangaroos. We confirm that this contraceptive system has potential for managing overabundant captive and selected wild populations of macropodid marsupials.

Habitat selection by adult female eastern grey kangaroos

We determined patterns of habitat selection in the winter–spring period by adult female eastern grey kangaroos (Macropus giganteus) at Yan Yean Reservoir Catchment near Melbourne, Victoria, during 1994–95. We assessed habitat selection at two levels by radio-tracking 11 adult female kangaroos. The 95% isopleth harmonic mean home-range size (mean = 62.3 ha) was the smallest recorded for female eastern grey kangaroos. No range encompassed all of the habitat types available in the study area, and the mix and rankings of habitats selected at this level varied amongst individuals when compared by compositional analysis with available habitats. Selection of habitats at the within-range level also varied among individuals and differed between night and day for many individuals, but not for the population mean. Individuals selected strongly for good foraging habitat within their ranges. In particular, grassy clearings were used by all individuals and were selected strongly by day, night or at both times.

Fertility Control of Eastern Grey Kangaroos: Do Levonorgestrel Implants Affect Behavior?

Wild populations of eastern grey kangaroos (Macropus giganteus) can pose serious management problems when conditions favor a high population growth rate. Contraception methods are becoming an ethically more acceptable alternative to culling or translocation when dealing with population control of large mammals. We investigated behavioral effects of levonorgestrel contraception in this species. A total of 82.4% of female eastern grey kangaroos treated with levonorgestrel implants did not reproduce, whereas only 12.5% of control females did not reproduce. Levonorgestrel contraception had no significant effect on time spent feeding, scanning, grooming, moving, and sexual interactions with males during the observation sessions. However, control females spent more time in open paddocks feeding than contracepted females over a 24-hr period. Males preferred to associate with groups containing more (and a higher percentage of) control females.