The common myna (Acridotheres tristis) is an invasive bird species that is native to Asia. Since being introduced around the world, the common myna has become an agricultural pest and poses a threat to native birds and ecosystems. In this article, we will explore the types of damage that the common myna causes and the impact it has on the environment.
Damage to Crops
One of the major problems caused by the common myna is damage to agricultural crops. As an omnivorous bird, the common myna feeds on fruits, grains, and vegetables. Some of the crops that are frequently damaged by common mynas include:
- Berries – Raspberries, blueberries, strawberries
- Fruit trees – Apples, cherries, peaches, citrus
- Vine crops – Grapes, kiwi
- Vegetables – Lettuce, cabbage, tomatoes, corn
- Cereal grains – Rice, wheat, barley, oats
Common mynas directly damage ripe fruits and grains by pecking holes in them to eat the flesh and seeds. They will also eat newly planted seeds and seedlings, destroying crops before they have a chance to grow. Flocks of birds can decimate fields, leaving farmer’s crops unsalvageable.
In addition to direct damage, common mynas spread disease and contamination in fields. Their feces and bacteria can infect fruits and vegetables, rendering them unsuitable for human consumption. Their droppings also spread weed seeds throughout fields.
Quantifying Crop Losses
Researchers have tried to quantify the economic impact of common myna damage to agriculture. One study in Australia estimated that common mynas caused $4.7 million in damage to grape crops alone per year. Another report estimated that mynas caused $16.7 million in damage across all affected crops annually in Australia.
In parts of their native range like India, common mynas are considered one of the most detrimental birds to agriculture. However, precise financial data is lacking in these regions.
Predation of Native Species
In addition to damaging crops, common mynas negatively impact native species, especially birds. Common mynas are aggressive and territorial. They will drive native birds from their nesting sites and compete for food resources.
Species that have been displaced by common mynas include:
- Bluebirds
- Woodpeckers
- Swallows
- Wrens
- Robins
- Chickadees
Common mynas possess adaptations that give them an advantage over native cavity nesting birds. They breed multiple times a year whereas native species may only breed once or twice annually. Mynas also begin breeding earlier in the spring, allowing them to claim prime nesting sites first. Additionally, mynas exhibit cooperative breeding behaviors where multiple birds work together to drive away competitors.
Decline of Native Birds
The decline of native birds caused by common mynas has been demonstrated scientifically through breeding bird surveys:
- In Vancouver, house sparrow populations dropped by 26% and western bluebird populations declined 16% following the arrival of mynas.
- Surveys in New Zealand over an 18 year period showed significant reductions in multiple native cavity nesting bird species as common myna populations increased.
- In South Africa, common mynas outcompeted native red-winged starlings and drove their populations down by more than 80% in some regions.
The reduction of native birds can have cascading ecological effects. Declines in insect-eating birds allows pest insect populations to thrive. Reduced pollination by nectar-feeding birds impacts plant reproduction. The overall biodiversity of habitats is diminished.
Solutions and Management
Controlling populations of destructive common mynas poses a significant challenge. Here are some of the techniques that have been utilized:
Population Culling
Methods to cull myna populations include:
- Trapping birds
- Shooting birds
- Poisoning birds
Culling requires persistent effort to overcome the mynas’ high reproduction rate. It is also controversial due to ethical concerns over harming animals.
Disrupting Nesting
Interfering with myna nesting by:
- Sealing cavities to prevent nest sites
- Removing existing nests and eggs
- Installing barriers on building ledges and crevices
These techniques must be continued regularly to have any long-term effect.
Enhancing Habitat for Native Species
Providing nest boxes and food sources specifically for native species can help them coexist with the myna invasion. However, adequate habitat must be maintained for this to work.
Conclusion
The common myna is an aggressively invasive bird that causes substantial damage. Through consumption of crops, usurping of native nest sites, and spread of disease, mynas exact heavy ecological and economic costs wherever they become established. Managing myna populations is an expensive and difficult process, underscoring the importance of preventing introductions of harmful non-native species. Preventing the common myna’s invasion in the first place is the most effective way to avoid the harms this species can inflict.