Wildlife

Geese

Canada Geese and Cackling Geese can cause damage by eating vegetation, and mess by leaving droppings. In some urban settings they can pose a further nuisance by alarming members of the public. They are often associated with stormwater management ponds. As many forms of LID reduce or eliminate standing water, the habitat for geese is reduced. However, geese have even been found nesting on extensive green roofs in our region.
Here are some tips on control:

1. Discourage the feeding of any wildlife: This may require public education with signage.
2. Discourage geese from taking off and landing: Geese require open space which can be broken up with fencing or vegetation barriers such as hedges
3. Mow less frequently: Geese prefer to eat the shorter, younger shoots of turf grass. Reducing mowing saves maintenance budget, and on vegetation filter strips and in enhanced grass swales the roughness (Manning's 'n') is increased. Increased roughness slows flow, allowing more water to infiltrate into the soil.
4. Bird deterrent tape: Geese are slightly discouraged by shiny/flickering/reflective movement. Foil tape or flags are available for this purpose. This can be a useful strategy on recently seeded areas or on green roofs, in the late winter, at the start of nesting season.

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  Geese raising their young on an extensive green roof, Toronto, ON

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Mosquitoes

Mosquitoes are a vector for many global diseases. In Ontario they are associated with transmission of West Nile Virus[1]. Low impact development technologies reduce the amount of standing water compared to traditional stormwater ponds as most water is stored in voids within soil and gravel layers. The maximum allowable surface ponding time is 24 hours after a storm event. This is less than the time required for one mosquito breeding cycle. But in high density urban landscapes, it may be desirable to have a shorter ponding time.

Where designs do include standing water (e.g. in rainwater harvesting), the following practices can reduce mosquito habitat further:

• Mesh is the first line of defense: A mesh size of 1.5 mm or smaller is recommended where a screen is used to exclude mosquitoes from a tank or other standing water[2],
• The Ministry of the Envionment and Climate Change permit just two larvicides to be used to kill mosquito larvae growing in the water[3]:
  1. Bacillus thuringiensis israeliensis (Bti):Note that provincial regulations permit only granular application, rather than 'dunks' or 'pucks' available elsewhere. This means frequent application may be necessary,
  2. Methoprene: This product can only be used by licensed individuals as it is slightly toxic to some fish species.
• Mineral oil or liquid soap: A small quantity of either one of these will disrupt mosquito larvae at the surface of the water. This can be effective in residential rain barrels, but requires regular application.

Airborne adulticides for mosquito control are permitted for use in Ontario. But their use is not recommended for most forms of stormwater control. Encouraging populations of bats, birds, dragonflies and other natural predators is worthwhile for improving biodiversity. But this has not been demonstrated as an effective means of mosquito control.

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  Mosquito larvae developing in water
  Image: James Gathany, CDC

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See Also

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1. REDIRECT Special:ArticleFeedbackv5

Low Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

Water ponded on the ground surface.

A thin layer of vegetation and growing medium installed on top of a conventional flat or sloped roof, also referred to as living roofs or rooftop gardens.

A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

Gravel, or crushed stone of various size gradations (i.e., diameter), used in construction; void forming material used as bedding and runoff storage reservoirs and underdrains in stormwater infiltration practices.