Ecological Impacts

Ecological Impacts and Management of the Canada Goose (Branta canadensis) on Vancouver Island, BC

The Canada goose (Branta canadensis) is a common sight along the British Columbia coast, particularly around Central and Southern Vancouver Island. However, this was not always the case. Canada geese were only migrants and winter visitors before a few geese were introduced in the 1920s and 30s (Dawe and Stewart 2010). These early introduction attempts yielded a small resident population of birds in the Victoria area, but it wasn’t until more intense introduction programs took place in the 1970s and 80s that the population really started to grow (Dawe and Stewart 2010). These introduction attempts were made by both government and private organizations in an effort to increase hunting opportunities around the island. Today, the population of resident geese is estimated to be 15,000 and is growing rapidly; the geese are often considered nuisances, and degradation of coastal and estuarine ecosystems, along with crops and agricultural land, is a major concern (Dawe and Stewart 2010; Isaac-Renton et al. 2010; RCGMS 2012).

Canada geese imprint on the area they were hatched and return to breed in that same area themselves. The combination of this life history trait with introduction programs has resulted in the growth of “resident” flocks which don’t have the urge to migrate (RCGMS 2012; Dawe and Stewart 2010; Dawe et al. 2011). This is a familiar problem for most of North America, and Vancouver Island is no exception. Resident geese have higher breeding success because they aren’t subjected to the high energy demands of migration; this allows more energy to be used for reproduction than their migratory counterparts (Dawe et al. 2011).

For example, no Canada geese were observed in the Englishman River estuary in June of 1974; however, by 2007 at least 73 nesting pairs were observed. The first pair of nesting Canada geese were observed on the Little Qualicum River estuary in the summer of 1984, and by 2010 at least 45 pairs were observed nesting (Dawe and Stewart 2010). Although these populations don’t seem excessive, it is clear that they are growing quickly. In the opinion of biologist Neil Dawe, the population of geese on Vancouver Island has already exceeded the carrying capacity for the region (Hume 2010; Dawe et al. 2011). Dawe et al. (2011) found that geese are altering the floral composition of East Coast Vancouver Island estuaries. Alterations of the plant community has caused erosion, affected nutrient-cycling, shading, and soil salinity levels. Changes to these factors has altered ecosystem functioning altogether, perhaps permanently (Dawe et al. 2011).

These changes have wide-ranging effects, which can be detrimental to all sorts of native species from invertebrates to fish to mammals and to other avifauna. Isaac-Renton et al (2010) found that grazing Canada geese in the nearby gulf islands are allowing the introduction of exotic annual grasses, which has negatively impacted the diversity of native plant species in maritime meadows. These ecosystems are already considered threatened, so the damage incurred by the relatively new resident Canada geese is highly unwelcome.

In the Capital Region of Vancouver Island, a “Regional Canada Goose Management Strategy” (RCGMS) is being developed to address the surging population of geese. In this region, goose-related problems include damage to agricultural crops, hazards at the Victoria International Airport, concerns over water quality, human/goose conflicts in parks, and environmental degradation of sensitive ecosystems (RCGMS 2012).

The overabundance of Canada geese on Vancouver Island poses a special management problem. Along with human/goose conflicts such as crop damage and airport safety, the geese are causing damage to local ecosystems, which in turn is affecting native flora and fauna (Dawe and Stewart 2010; Isaac-Renton et al. 2010; RCGMS 2012). At the very least, long-term stabilization of the population is needed to ensure that these problems don’t become worse. However, although introduced, euthanization of resident geese to rectify these problems is frowned upon by the majority of the general public (Braband and Clark 1991; Lefebvre unknown; Hume 2010). Biologist Neil Dawe believes that in order to protect local estuarine ecosystems, Canada geese may have to be eradicated altogether (Hume 2010). In reality, despite damage to local ecosystems clearly caused by the geese, public opposition to a cull makes it an unlikely solution. This means that it is up to wildlife managers to bring the population growth under control, which can be done through hunting and egg addling (RCGMS 2012). Hunting is another management tool, however many of the resident goose populations utilize urban areas, where hunting isn’t an option due to nearby proximity of houses and bystanders (RCGMS 2012; Smith et al. 1999). Hazing of geese to chase them out of areas where they are a problem isn’t a long-term solution, as the geese just become a problem elsewhere and/or eventually return to the original area (RCGMS 2012; Smith et al. 1999). The Regional Canada Goose Management Strategy (2012) predicts that the growth in the population of Canada geese in the Capital Region can be curbed through annual egg addling and removing just 100 adult birds per year by hunting. In fact, if carried out on an annual basis, this management strategy would eventually cause a decrease in the population (RCGMS 2012).

As for the remainder of the Southeast Coast of Vancouver Island, it is likely that similar measures will need to be implemented in order to control population growth. In some areas, the population will at least have to be reduced to a point that meets the carrying capacity of the local ecosystem (Dawe et al. 2011). Canada geese are a familiar sight that many people enjoy and associate with nature. However, special attention should be directed towards their management to ensure that the geese don’t continue to degrade important habitats for other species, particularly because they are introduced to the region.

References:

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