Friday, 20 July 2012

The impact of the introduced Common Myna on the Birds of Canberra.

The Common Myna (Acridotheres tristis) originates in India and South Asia, but has been introduced to many other parts of the world, both as a control for insect pests and as a pet that has gone wild. It thrives in urban environments, forming large noisy and visible roosting colonies, except in the mating system when it nests in cavities and is highly territorial. It is widely blamed for declines in native bird populations, and is considered the world's third most invasive species by the IUCN Species Survival Commission. It is considered particularly harmful in Australia, where native species often prove vulnerable to competition by introduced animals. However despite being widely cited as a dangerous invasive species, there has been little empirical evidence of the impact of Common Mynas on native species to date.

A Common Myna in North-West Province, South Africa. biodiversity explorer/Johan van Rensburg.

In a paper published in the journal PLoS One on 11 July 2012, a team of scientists led by Kate Grarock of the Fenner School of Environment and Society at the College of Medicine, Biology and Environment at the The Australian National University in Canberra, examine the impact of the spread of Common Mynas through Canberra over 29 years, starting from 1981, using data collected by the Canberra Ornithologists Group as part of the Canberra Garden Bird Survey.

Common Mynas are thought to impact on populations of other Birds in three ways. Firstly, they form large populations, and consume correspondingly large quantities of food, presumably to the detriment of other Birds with similar food requirements. Secondly, Common Mynas are cavity-nesting birds, and will presumably compete for available nesting places with other cavity-nesting species. Thirdly the birds are highly territorial during the mating season, maintaining large territories from which they actively exclude other insectivorous birds.

Common Mynas were introduced to Melbourne in 1862 as an insect control measure, since when they have been spreading across Australia. They were first seen in Canberra in 1968, since when the population has increased steadily. For the purpose of the study Grarock et al. divided Canberra into study four  areas, numbered Regions 1-4, and the year into two seasons, breeding (September to February) and non-breeding (March to August). Common Mynas were established in Region 3 before the study began, and spread to Region 4 in 1989, Region 1 in 1991 and Region 2 in 1993.

The location of the four study areas (right) in the Australian Capitol Territory (bottom left), and country as a whole (top left). Grarock et al. (2012).

Grarock et al. studied twenty different species of cavity-nesting, small and large insectivorous Birds, to assess the impact the spread of the Common Myna had on their populations.

Sulphur-crested Cockatoos (Cacatua galerita) are large cavity-nesting Parrots that were found to be increasing in numbers by an average of 10.3 new Birds per km³ per year. Where the Mynas became established this rise in population fell to 8.3 new Birds per year per km³. Thus the Mynas did impact negatively upon the Cockatoos, but only in that they were able to slow a high population growth rate by about 20%.

The Sulphur-crested Cockatoos (Cacatua galerita), had its population growth slowed but not halted by the expansion of the Common Mynah. WWF.

The Crimson Rosella (Platycercus elegans) is another cavity-nesting Parrot, that was also undergoing population growth during the study period. In areas without Common Mynas the Crimson Rosella population grew by an average of 5.9 Birds per km³ per year, but where Common Mynas were introduced this rate of growth fellto 2.4 new Crimson Rosellas per km³ per year, a drop in population expansion of about 60%. Thus the Common Mynas clearly had an impact on the Common Rosellas, but again only in that they slowed a high rate of population expansion.

The Crimson Rosella (Platycercus elegans), also had its population growth slowed by the presence of Common Mynas. Australian Museum.

The Laughing Kookaburra (Dacelo novaeguineae) is a large, cavity-nesting member of the Kingfisher Family (Halcyonidae). This did suffer a direct fall in population where the Common Myna became established, with a drop in population density of 0.4 Birds per km³; in areas where the Common Myna was not present the population remained static, suggesting that the presence or absence of Common Mynas was the only environmental variable that changed for the Kookaburra during the study period.

The Laughing Kookaburra (Dacelo novaeguineae) did suffer a direct drop in population density as a result of the presence of Common Mynas. National Geographic.

The Galah (Eolophus roseicapilla) is another large cavity-nesting member of the Cockatoo Family (Cacatuidae), which does extremely well in human modified environments, and which is thought to have expanded its range significantly at the expense of other forms of Parrot since the arrival of European settlers in Australia. No correlation could be found between populations of Galahs and those of Common Mynas, the Galahs apparently being unaffected by the invaders.

The Galah (Eolophus roseicapilla), was apparently unaffected by the presence of Common Mynas. Australian Museum.

The Australian King Parrot (Alisterus scapularis) is another cavity-nesting Parrot. Like other Parrot species these Birds often do well in garden environments, and are thought to be expanding their numbers in many urban and suburban areas across eastern Australia. These Parrots were also apparently unaffected by the presence of Common Mynas.

The Australian King Parrot (Alisterus scapularis), also apparently unaffected by the presence of Common Mynas. National Geographic.

The Eastern Rosella (Platycercus eximius) is another cavity-dwelling Parrot that does well in human-modified environments. This also was apparently unaffected by the presence of Common Mynas.

The Eastern Rosella (Platycercus eximius), apparently unaffected by the presence of Common Mynas. Birdlife Australia.

The Common Starling (Sturnus vulgaris) is another cavity-dwelling introduced species, this time from Europe. Like the Common Myna it was originally introduced to the Melbourne area as a pest control measure, and has subsequently spread across much of the continent. It is considered a threat to many native species, as it breeds rapidly and is highly aggressive. The birds are also considered a serious agricultural pest, particularly due to its tendency to damage soft fruit, and a vector for invasive plant species. Starlings also do extremely well in urban and suburban environments. Perhaps unsurprisingly, the Starlings were unaffected by the presence of Common Mynas.

The Common Starling (Sturnus vulgaris), a highly invasive European species, unaffected by the presence of Mynas. Columbia University.

The Superb Fairywren (Malurus cyaneus) is a small insectivorous Bird common across southeastern Australia. It typically does very well in urban and suburban environments, and underwent significant increases in numbers during the study period, however it was strongly affected by the presence of Common Mynas, undergoing significant declines in numbers wherever these appeared.

The Superb Fairywren (Malurus cyaneus), a normally persistent native species that suffered badly when Common Miners colonized an area. Only the males have this distinctive plumage, the females are a dull brown. The Royal Botanic Gardens, Sydney. 

The Striated Pardalote (Pardalotus striatus) is another small insectivorous Bird common across much of Australia. Like the Superb Fairywren it was undergoing an expansion in population numbers in Canberra during the study period, but suffered a sharp fall in numbers whenever the Common Myna became established.

The Striated Pardalote (Pardalotus striatus), another small insectivorous Bird badly affected by the presence of Common Mynas. The Royal Botanic Gardens, Sydney.

The Willie Wagtail (Rhipidura leucophrys) is another small insectivorous Bird common across Australia. This was also badly affected by the presence of Common Mynas, and suffered population drops where these had become established.

The Willie Wagtail (Rhipidura leucophrys), a widespread Australian Bird badly affected by the Common Myna. Canberra Garden Bird Survey.

The Grey Fantail (Rhipidura albiscapa) is another small, widespread, insectivorous Australian Bird. This was also undergoing a rise in population numbers in Canberra during the time of the study, but suffered a sharp drop in numbers wherever the Common Myna became established.

The Grey Fantail (Rhipidura albiscapa), another successful Australian Bird that suffered here Common Mynas became established. University of Cape Town.

The Magpie Lark (Grallina cyanoleuca) is another small insectivorous Bird that does well in urban and suburban settings. This was also undergoing an increase in population density during the study period, but again suffered a sharp decline in numbers where Common Mynas became established.

The Magpie Lark (Grallina cyanoleuca) another small insectivorous Bird affected badly by the Common Myna. ABC.

The Silvereye (Zosterops lateralis) is a small omnivorous Bird common in Australian gardens, where it is often considered a pest due to its habit of damaging fruit. This was also undergoing a population increase in the Canberra area during the study period, but again suffered a sharp drop in population density where Common Mynas became established.

The Silvereye (Zosterops lateralis), a small omnivorous Bird that suffered a drop in population density where the Common Myna became established. The Age.

The Common Blackbird (Turdus merula) is another European Bird introduced to Melbourne in the 1850s that has subsequently spread across much of Australia. It is primarily insectivorous, but is considered a pest due to its tendency to damage fruit and to spread seeds of invasive plant species such as European Blackberry (Rubus fruticosus). It is also highly aggressive and competes with native Birds for food and nesting sites. The Blackbird was another species undergoing an expansion in numbers that suffered a sharp drop in population density where the Common Myna became established.

The Common Blackbird (Turdus merula) a European Bird considered an invasive pest that did badly where Common Mynas became established. Canberra Indian Myna Action Group/Helen Fallow.

The House Sparrow (Passer domesticus) is another introduced European species considered an invasive pest due to its high breeding rate and tendency to compete with native birds. The House Sparrow suffered a collapse in population numbers during the study period, however this began in many areas before the appearance of Common Mynas, so it was difficult to establish what (if any) role the Mynas had in the Sparrow's decline.

The House Sparrow (Passer domesticus), an invasive European species that suffered a sharp fall in numbers during the study, but which was apparently unrelated to the presence of Common Mynas. BBC.

The Red Wattlebird (Anthochaera carunculata) is a large native Bird which is primarily a nectar feeder, but which also takes a considerable amount of insect food. This underwent a steady increase in population density during the study period, and was apparently unaffected by the presence of the Common Myna.

The Red Wattlebird (Anthochaera carunculata) is a large, partially insectivorous bird apparently unaffected by the presence of the Common Myna. Sydney Nature.

The Noisy Friarbird (Philemon corniculatus) is another large native Bird, which consumes nectar, insects and fruit. This suffered a decline in population across Canberra during the study period, but again this appeared to be independent of the presence of Common Mynas.

The Noisy Friarbird (Philemon corniculatus) suffered a decline in population during the study period, but this did not seem to be influenced by the presence of Common Mynas. Monash University.

The Australian Magpie (Gymnorhina tibicen) is a large omnivorous Bird which takes a considerable amount of Insect prey. Although superficially Crow-like, it is more closely related to the Butcher Birds. Australian Magpies underwent a rise in numbers during the study period, and were apparently unaffected by Common Mynas.

The Australian Magpie (Gymnorhina tibicen), a large, partially insectivorous Bird, apparently unaffected by Common Mynas. University of South Australia

The Pied Currawong (Strepera graculina) is another large omnivorous Bird that eats a substantial amount of insect prey. Like the Australian Magpie it is superficially Crow-like, but more closely related to the Butcher Birds. The Pied Currawong did not undergo any significant change in population size during the study period.

The Pied Currawong (Strepera graculina), a large omnivorous Bird that did not undergo any significant change in population size during the study period. Australian Museum.

The Australian Raven (Corvus coronoides) is a true member of the Crow family. It is a large omnivorous Bird that consumes significant amounts of insects, and does well in urban environments. Like other large omnivorous Birds it was apparently unaffected by the presence of Common Mynas, and underwent a steady rise in numbers throughout the study period.

The Australian Raven (Corvus coronoides) was apparently unaffected by the presence of Common Mynas. The Royal Botanic Gardens, Sydney.

The study suggests that the Common Myna does have a strong adverse impact on small insectivorous Birds, but that bigger Birds were largely immune from this. The impact on cavity-nesting Birds was more complicated, with some Birds affected and others not; no cavity-nesting Bird appeared to be seriously threatened by the presence of Common Mynas.

Kate Grarock has a Facebook page for her Canberra Bird research.

See also Floating Japanese dock brings fears of invasive species to OregonVelvet Geckos and Broad-headed Snakes; understanding the population structure of a favored prey item in order to help protect an endangered predatorWhat killed the Australian Thylacine? Canberra shaken by mild Earthquake and Birds on Sciency Thoughts YouTube.

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1 comment:

  1. Wow! that was indeed a very informative article. I am glad to learn the important of common myna. Great blog!

    ReplyDelete