Kangaroos are not “highly fecund” as reported in the Australian Government Department of Environment’s 2014 Report on the commercial harvest of kangaroos in Australia provided to the Californian government.
Kangaroos are slow-growing species with low reproductive rates and high juvenile mortality. Contrary to common belief, kangaroos cannot raise to three joeys to independence per year.
Kangaroos are slow-growing species with low reproductive rates and high juvenile mortality. Contrary to common belief, kangaroos cannot raise to three joeys to independence per year.
Reproduction
- Embryonic diapause, where the growth of a 70-100 celled blastocyst is suspended in the ovary, does not confer any super-fecundity on a kangaroo. It simply delays normal growth of an embryo.
- Embryonic diapause is rare in Eastern Grey Kangaroos, and unknown in Western Grey Kangaroos. [1]
- Development of a dormant blastocyst (embryonic joey) can only occur when the previous joey has died or has permanently left the pouch, and is triggered by reduction in lactation rates. [2],[3]
- Thus a kangaroo doe can carry a growing in-pouch joey while nursing another at-foot dependent joey.
- It takes ~13 months for a Red Kangaroo joey to fully wean; up to 14 months for an Eastern Wallaroo and 17 months for a Euro; and 18+ months for an Eastern or Western Grey joey to fully wean. [4],[5]
- Twinning is rare, and survival of twins to weaning not recorded. [6],[7]
- A kangaroo doe can raise just one joey to full independence per year.
Breeding ages
- The average kangaroo doe’s fertile life is ~8 years. [8], [9]
- A doe’s first joey is the most likely to die. She will first successfully raise her young at about ~3 yrs, [10] with that joey weaning when she is ~4 yrs.
- By ~12 yrs – if the doe lives that long [11] – few females continue to produce offspring. [12]
Juvenile mortality
- Wild kangaroo juvenile mortality in the first year of life is similar to other mammals in that it is high [13] – around 73% [14] in optimal natural conditions. 50% of emergent young Eastern Grey joeys still dependent on their mothers have been recorded as being taken by foxes. [15]
- During drought juvenile mortality can be up to 100%. [16]
- Applying 73% juvenile mortality, and assuming optimal breeding conditions every year of her breeding life, a doe might have two joeys survive to weaning in her lifetime (up to 3 in Reds), [17], [18] but only if she lives a full and successful fertile life with a lifetime of good environmental conditions, which is "unrealistic". [19]
- Further, kangaroo does surviving drought in their lifetime then "wean less offspring and their daughters wean fewer grandoffspring"[19]
- Adult mortality rates then apply, varying with environmental changes and threats.
Population growth rate
- "Rapid increases" do not "typically follow the breaking of drought conditions" [20] as reported by the Australian government in its 2014 report to the California Department of Fish and Wildlife.
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John Kelly, CEO
Kangaroo Industry Association of Australia
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- Kangaroo populations can only grow gradually. Actual wild population growth rates (PGR) are a maximum of ~8-10% pa [22] (and a calculated ~14% for reds [23] ) under good conditions.
- If left undisturbed in continuing optimal natural conditions, kangaroo populations do not keep infinitely increasing, but tend towards equilibrium or stability. [24], [25], [26],[27]
- During drought populations collapse with up to 100% joey mortality [28], [29] and up to 60% adult mortality [30], [31], [32] with commensurate population declines.
- Read more here - Kangaroos continue to be shot beyond reproductive capacity with shooting quotas of 15–20% [33] and un-collated levels of landowner and illegal shooting, even during drought when populations decline.
Banner image: Mariel Becker
female Eastern Grey Kangaroo with pouch young joey: Macropus giganteus
female Eastern Grey Kangaroo with pouch young joey: Macropus giganteus
Reproduction
[1] Dawson T (2012) Kangaroos: biology of the largest marsupials Comstock Publishing Associates, New York
[2] Dawson T (2012)
[3] Tyndale-Biscoe H (2005) Life of Marsupials CSIRO Publishing Collingwood Australia
[4] Poole WE (1975) Reproduction in the Two Species of Grey kangaroos, Macropus Giganteus Shaw and M. Fuliginosus (Desmarest). II. Gestation, Parturition and Pouch Life Australian Journal of Zoology 1975 23(3) 33-353
[5] Dawson (2012)
[6] Dawson (2012)
[7] Poole WE (1975)
Breeding ages
[8] Dawson,T (2012) Kangaroos: Biology of the Largest Marsupials Cornell University Press. Ithaca, US Based on Table 6.1
[9] Bilton A & Croft D (2004) Lifetime Reproductive Success in a Population of Female Red Kangaroos Macropus Rufus in the Sheep Rangelands of Western New South Wales: Environmental Effects and Population Dynamics Australian Mammalogy 26: 45-60, Graphic Services Pty Ltd, Northfield SA
[10] Bilton & Croft (2004)
[11] The average lifetime of a female (Red Kangaroo) was ~13 years (Bilton & Croft 2004)
[12] Arnold GW, Grassia A, Steven DE, Weeldenburg JR (1991) Population ecology of western grey kangaroos in a remnant of Wandoo Woodland at Bakers Hill, southern Western Australia Wildlife Research 18(5) 561-575, CSIRO Publishing, Melbourne
Juvenile mortality
[13] Caughley, G (1967) Calculations of population mortality rate and life expectancy for thar and kangaroos from the ratio of juveniles to adults New Zealand Journal of Science 10: 578–584
[14] Arnold GW et al (1991)
[15] Banks et al (2000) Predation by red foxes limits recruitment in populations of eastern grey kangaroos Austral Ecology (2000) 25, 283–291
[16] Shepherd N (1987) Condition and recruitment of kangaroos in Kangaroos: their ecology and management in the sheep rangelands of Australia (Eds: Caughley G, Shepherd N, Short J) Cambridge University Press, Cambridge
[17] Bilton & Croft (2004)
[18] Dawson (2012)
[19] Bilton and Croft (2004)
Actual population growth rate
[20] Australian Government Department of the Environment Report on the commercial harvest of kangaroos in Australia April 2014. Pg2
[21] ABC News online (5 Jan 2015) Kangaroo population explodes in western Queensland. (Source 7pm TV News QLD) Available from <http://www.abc.net.au/news/2015-01-05/kangaroo-population-explodes-in-western-queensland/5999846> [24 Aug 2015)
[22] Arnold GW, Grassia A, Steven DE, Weeldenburg JR (1991) Population ecology of western grey kangaroos in a remnant of Wandoo Woodland at Bakers Hill, southern Western Australia Wildlife Research 18(5) 561-575, CSIRO Publishing, Melbourne. **Arnold’s exponential growth rates equate to Western Grey population growth rates of x7.86% pa over 4 years, and then x8.47% pa over a subsequent 6 years.
[23] Caughley, G Shepherd, N Short, J (eds) (1987) Kangaroos : their ecology and management in the sheep rangelands of Australia. Cambridge University Press, Melbourne, Australia..
[24] Bilton & Croft (2004)
[25] Bayliss P (1985) The Population Dynamics of Red and Western Grey Kangaroos in Arid New South Wales, Australia. I. Population Trends and Rainfall. The Journal of Animal Ecology, Vol. 54, No. 1. (Feb., 1985), pp. 111-125.
[26] Wilson GR (1975) Age Structures of Populations of Kangaroos (Macropodidae) taken by Professional Shooters in New South Wales Australian Wildlife Research, 1975 2, 1-9, CSIRO Publishing, Melbourne
[27] Arnold GW, Grassia A, Steven DE, Weeldenburg JR (1991) Population ecology of western grey kangaroos in a remnant of Wandoo Woodland at Bakers Hill, southern Western Australia Wildlife Research 18(5) 561-575, CSIRO Publishing, Melbourne
[28] Shepherd N (1987) Condition and recruitment of kangaroos in Kangaroos: their ecology and management in the sheep rangelands of Australia (Eds: Caughley G, Shepherd N, Short J) Cambridge University Press, Cambridge
[29] Newsome AE (1971) The Ecology of Red Kangaroos Australian Zoologist, 16(1), 1971, p38
[30] Robertson G (1986) The Mortality of Kangaroos in Drought 1986 Australian Wildlife Research 13(3) 349 – 354
[31] Newsome AE, Stephens DR, Shipway AK (1967) Effect of a long drought on the abundance of Red Kangaroos in central Australia CSIRO Wildlife Rescue 12: 1-8
[32] Caughley, G , Grigg, GG, Smith L. (1985). The effect of drought on kangaroo populations. Journal of Wildlife Management 49: 679-685.
[33] Department of Sustainability, Environment, Water, Population and Communities (2012) Commercial kangaroo harvesting fact sheet Australian Government. <http://www.environment.gov.au/biodiversity/wildlife-trade/publications/commercial-kangaroo-harvesting-fact-sheet-2012> [23 Aug 2015]
[1] Dawson T (2012) Kangaroos: biology of the largest marsupials Comstock Publishing Associates, New York
[2] Dawson T (2012)
[3] Tyndale-Biscoe H (2005) Life of Marsupials CSIRO Publishing Collingwood Australia
[4] Poole WE (1975) Reproduction in the Two Species of Grey kangaroos, Macropus Giganteus Shaw and M. Fuliginosus (Desmarest). II. Gestation, Parturition and Pouch Life Australian Journal of Zoology 1975 23(3) 33-353
[5] Dawson (2012)
[6] Dawson (2012)
[7] Poole WE (1975)
Breeding ages
[8] Dawson,T (2012) Kangaroos: Biology of the Largest Marsupials Cornell University Press. Ithaca, US Based on Table 6.1
[9] Bilton A & Croft D (2004) Lifetime Reproductive Success in a Population of Female Red Kangaroos Macropus Rufus in the Sheep Rangelands of Western New South Wales: Environmental Effects and Population Dynamics Australian Mammalogy 26: 45-60, Graphic Services Pty Ltd, Northfield SA
[10] Bilton & Croft (2004)
[11] The average lifetime of a female (Red Kangaroo) was ~13 years (Bilton & Croft 2004)
[12] Arnold GW, Grassia A, Steven DE, Weeldenburg JR (1991) Population ecology of western grey kangaroos in a remnant of Wandoo Woodland at Bakers Hill, southern Western Australia Wildlife Research 18(5) 561-575, CSIRO Publishing, Melbourne
Juvenile mortality
[13] Caughley, G (1967) Calculations of population mortality rate and life expectancy for thar and kangaroos from the ratio of juveniles to adults New Zealand Journal of Science 10: 578–584
[14] Arnold GW et al (1991)
[15] Banks et al (2000) Predation by red foxes limits recruitment in populations of eastern grey kangaroos Austral Ecology (2000) 25, 283–291
[16] Shepherd N (1987) Condition and recruitment of kangaroos in Kangaroos: their ecology and management in the sheep rangelands of Australia (Eds: Caughley G, Shepherd N, Short J) Cambridge University Press, Cambridge
[17] Bilton & Croft (2004)
[18] Dawson (2012)
[19] Bilton and Croft (2004)
Actual population growth rate
[20] Australian Government Department of the Environment Report on the commercial harvest of kangaroos in Australia April 2014. Pg2
[21] ABC News online (5 Jan 2015) Kangaroo population explodes in western Queensland. (Source 7pm TV News QLD) Available from <http://www.abc.net.au/news/2015-01-05/kangaroo-population-explodes-in-western-queensland/5999846> [24 Aug 2015)
[22] Arnold GW, Grassia A, Steven DE, Weeldenburg JR (1991) Population ecology of western grey kangaroos in a remnant of Wandoo Woodland at Bakers Hill, southern Western Australia Wildlife Research 18(5) 561-575, CSIRO Publishing, Melbourne. **Arnold’s exponential growth rates equate to Western Grey population growth rates of x7.86% pa over 4 years, and then x8.47% pa over a subsequent 6 years.
[23] Caughley, G Shepherd, N Short, J (eds) (1987) Kangaroos : their ecology and management in the sheep rangelands of Australia. Cambridge University Press, Melbourne, Australia..
[24] Bilton & Croft (2004)
[25] Bayliss P (1985) The Population Dynamics of Red and Western Grey Kangaroos in Arid New South Wales, Australia. I. Population Trends and Rainfall. The Journal of Animal Ecology, Vol. 54, No. 1. (Feb., 1985), pp. 111-125.
[26] Wilson GR (1975) Age Structures of Populations of Kangaroos (Macropodidae) taken by Professional Shooters in New South Wales Australian Wildlife Research, 1975 2, 1-9, CSIRO Publishing, Melbourne
[27] Arnold GW, Grassia A, Steven DE, Weeldenburg JR (1991) Population ecology of western grey kangaroos in a remnant of Wandoo Woodland at Bakers Hill, southern Western Australia Wildlife Research 18(5) 561-575, CSIRO Publishing, Melbourne
[28] Shepherd N (1987) Condition and recruitment of kangaroos in Kangaroos: their ecology and management in the sheep rangelands of Australia (Eds: Caughley G, Shepherd N, Short J) Cambridge University Press, Cambridge
[29] Newsome AE (1971) The Ecology of Red Kangaroos Australian Zoologist, 16(1), 1971, p38
[30] Robertson G (1986) The Mortality of Kangaroos in Drought 1986 Australian Wildlife Research 13(3) 349 – 354
[31] Newsome AE, Stephens DR, Shipway AK (1967) Effect of a long drought on the abundance of Red Kangaroos in central Australia CSIRO Wildlife Rescue 12: 1-8
[32] Caughley, G , Grigg, GG, Smith L. (1985). The effect of drought on kangaroo populations. Journal of Wildlife Management 49: 679-685.
[33] Department of Sustainability, Environment, Water, Population and Communities (2012) Commercial kangaroo harvesting fact sheet Australian Government. <http://www.environment.gov.au/biodiversity/wildlife-trade/publications/commercial-kangaroo-harvesting-fact-sheet-2012> [23 Aug 2015]