Hyperabundant species management
The preservation of ecological integrity is a crucial part of natural area conservation.
Ecological Integrity: The components and processes that are typical of a healthy ecosystem are intact and working, supporting the native species that live there.
Maintenance and restoration of ecological integrity has been legislated as the first priority for the management of National Parks in the "Canada National Parks Act" (2000). Parks Canada, being charged with this responsibility, takes actions to protect the ecological integrity of habitats in national parks, and contributes to the management and recovery of species at risk. These actions can include the management of hyperabundant wildlife populations.
A species is considered hyperabundant when its population has grown too large for the natural area to support it, and/or when it negatively affects species at risk. Native species generally become hyperabundant as a result of human-induced changes to the ecosystem that cause their populations to grow unchecked. The "Directive on the Management of Hyperabundant Wildlife in Parks Canada’s Heritage Places" (2019) states that hyperabundant wildlife populations must be actively managed in national parks when:
- Population growth is no longer fully regulated or kept in check by natural processes, and
- Research suggests that species at risk, ecological health, and/or ecological sustainability have been or are likely to be damaged or compromised by the hyperabundant populations.
Monitoring and research at Point Pelee National Park have identified two hyperabundant wildlife populations: white-tailed deer (on the mainland) and double-crested cormorants (on Middle Island). The size of these populations are a threat to species at risk and to the natural processes that are expected in this ecological region of Canada.
Mainland vegetation and white-tailed deer (Odocoileus virginianus)
- Climate Change: Warmer winters with less snow cover resulting from climate change, increases food availability and winter survival rates;
- Lack of Predators: Large predators would normally keep deer populations in check. When large numbers of settlers arrived in Southwestern Ontario including the Point Pelee Peninsula, large portions of forest areas were converted to farmland or residential areas and no longer provided habitat for large predators like bears, cougars and wolves, who need large ranges. Settlers also aggressively hunted these predators until the last were extirpated from this area in the 1800s.
- Landscape changes: Human alterations to the landscape can create conditions where deer thrive. Deer adapted to the agricultural landscape where habitat edges along farm fields provided ideal areas for grazing and cover. When farming ceased in the park in the 1970s and these farms were abandoned. The land regenerated and young forests with lots of leafy and woody food became available for deer, which also boosted their populations.
Studies on browsing and forest health first linked deer browsing to negative impacts on the park’s vegetation communities in the late 1980s, and surveys have been conducted to document the deer population in the park since 1987. Based on guidelines for general forest regeneration and development, it is estimated that the park could support 24 to 32 deer (6 to 8 deer per km2) without adversely affecting forest regeneration. The current deer population is higher than the park’s capacity. The ongoing need for deer management is identified in Point Pelee National Park’s Management Plan, State of the Park Report, and Integrated Vegetation Management Plan.
Each year, forest health indicators are monitored and the deer population is counted. These data are important, as they inform decisions on how to make adjustments to deer management operations. Parks Canada staff consult with Caldwell First Nation to plan each year’s deer herd reduction. The park is closed to the public during the reduction activities.
The goal of hyperabundant deer management at Point Pelee National Park is to restore and maintain the ecological health of the natural habitats in the park. Point Pelee is committed to adapting management decisions over time, based on data gathered from research and monitoring. When data show that the deer population can be supported by the vegetation in the park, without significantly compromising species at risk or the health of the natural systems, then management actions for deer will be re-evaluated.
Middle Island and double-crested cormorants (Phalacrocorax auritus)
In 2000, the Nature Conservancy of Canada transferred Middle Island, the southernmost land area in Canada, to Point Pelee National Park. It is an important part of the small Carolinian ecozone, which makes up only 1% of the Canadian landmass. The island’s landscape provides clues into what a lot of southern Ontario looked like before European settlement. Middle Island is also home to several species at risk, designated by the Canada Species at Risk Act and/or the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) These species include blue ash, common hoptree, Kentucky coffee tree, red mulberry, wild hyacinth, eastern foxsnake, Lake Erie watersnake, barn swallow, shagreen, eastern banded tigersnail, and monarch butterfly.
In 1987, there were 3 double-crested cormorant nests found on the island. Thirteen years later, when Parks Canada acquired the island, this had increased to 5,202 nests, and vegetation monitoring was showing a drastic reduction in forest canopy cover. Though cormorants are native to North American, their population has exploded in recent years. Four main events are believed to have contributed to an increase in cormorant population numbers:
- Changes in fish populations in the Great Lakes: Increased availability of certain fish species, such as newly introduced invasive species (e.g. alewives and round gobies), produced new food sources for cormorants; and
- Increased over winter survival: This is linked to catfish farms in the southern United States, which can act as a reliable supply of food for cormorants.
- The banning of DDT and associated pesticides: This was a needed action to address DDT toxicity and its persistence in the environment which causes it to bioaccumulate (build up in living tissues) and biomagnify (increase in concentration in moving up the food chain). With the banning of this pesticide, concentrations in the environment decreased, improving cormorant breeding success and therefore increasing cormorant populations;
- Changes to federal and state conservation laws: These changes offered additional protection to cormorants;
Research and monitoring revealed that the high number of cormorant nests on the island was causing significant and potentially irreversible damage to the island’s native vegetation communities, and was threatening the species at risk that call Middle Island home.
Published research has linked declines in forest cover with double-crested cormorant nest numbers on several islands in the Lake Erie western basin, including Middle Island (1). This loss in forest cover reduces the available habitat for other colonial waterbird species on Middle Island, such as great blue herons and black-crowned night herons, that depend on it for breeding. Research on individual colonies has shown that double-crested cormorants can displace other nesting waterbirds through habitat loss, and direct competition for nests and nesting sites.Other cormorant-driven impacts on Middle Island have included reduced diversity in understory vegetation and changes in the distribution and composition of native fauna.
Point Pelee’s Management Plan, State of the Park Report, and Integrated Vegetation Management Plan all identify hyperabundant double-crested cormorants as a threat to the habitats and species at risk on Middle Island. Without intervention, the biologically diverse vegetation and complex ecosystem on Middle Island would be lost entirely.
Cormorant reduction is species-specific, logistically and economically feasible, and immediately effective (which is necessary for the high number of cormorant nests on Middle Island). Based on recommendations from the Parks Canada Animal Care Committee, cormorant reduction is planned for early in the nesting season, before egg hatching, to avoid impacts on cormorant young. Scarecrows and nest removal activities are used in specific areas on Middle Island, where individual species at risk need protection. These methods are not suitable for use over the whole island, but are effective when applied to smaller areas.
Double-crested cormorants are native within the Great Lakes, so the goal of their management on Middle Island is not to eliminate them. Instead, the goal is to reduce the number of nests, in order to restore ecological health and protect species at risk. The target for the density of cormorant nests on the island is 30-60 nests per hectare, in keeping with what would allow the island’s diverse native vegetation communities to persist. As of 2017, research and monitoring has shown an increase in healthy forest canopy cover, desirable herbaceous species, and many species at risk populations. These are good indicators that current management actions are working.
Monitoring of cormorant nests, vegetation health, and species at risk populations will continue on Middle Island. Hyperabundant species management is adaptive, so that it can be changed as conditions change, as the number of cormorant nests change, or as new information becomes available.
Public access to Middle Island is prohibited between March 1st and September 1st each year. This is required in order to minimize disturbance to nesting colonial waterbirds on the island (such as great egrets, great blue herons, black-crowned night herons, and herring gulls, in addition to double-crested cormorants), and to prevent danger to visitors when cormorant reduction activities are taking place.
The Middle Island Conservation Plan, which details how cormorant nesting numbers on Middle Island are managed, was developed in consultation with First Nations, partners, stakeholders, communities, and the public.
1) See Hebert et al., 2014. Nesting Cormorants and Temporal Changes in Island Habitats. Journal of Wildlife Management 78:307-313.