Knowing the Double Crested Cormorant: Behavioural Ecology and Public Education of Double-crested Cormorants at Tommy Thompson Park
This project includes both a scientific research paper and a public education poster focused on double-crested cormorants (Phalacrocorax auritus) at Tommy Thompson Park, Toronto, ON. Since my master's includes wildlife ecology and environmental interpretation, I wanted to study cormorants from both scientific and education perspectives. Together with Gail Fraser, I collected observational data on male cormorant advertising displays over the 2014 nesting season. From the results of this behavioural ecology study I wrote a formal scientific research paper which is included in this report. In the literature, cormorant research has been focused primarily on management and topics associated with human-cormorant conflict, leaving a gap in knowledge regarding understanding of basic cormorant behaviours including advertising. Outcomes of my research may have management implications, but my study's primary focus was a greater understanding of cormorant behaviour. A deep understanding of ecological processes, wildlife, and ecosystems is an important foundation for environmental education. Knowledge gained through ecological research enables environmental educators to provide accurate, pertinent information to the general public. With suggestions and advice from Karen McDonald, Park Manager at Tommy Thompson Park, I created a public education poster on cormorants. Cormorants are a controversial bird. Their reputation is clouded by misconceptions and a long history of human-wildlife conflict. Focusing on the same subject from both scientific and education perspectives was rewarding as I was able to practice and facilitate different ways of knowing: I believe that it is by knowing and experiencing the natural world that we can begin to live in right relationship with the land. 1 The Double-Crested Cormorant: The Most Controversial Waterbird on the Great Lakes1 1 The following paragraphs focused on cormorant controversy were adopted from: Mc Rae, M. (2014) Misconceptions and management of the double-crested cormorant. Unpublished manuscript, Applied Ecology, York University, Canada. The double-crested cormorant (Phalacrocorax auritus, hereafter cormorant) is the most controversial waterbird on the Great Lakes. Supported by a long culture history of human-wildlife conflict, current perceptions and attitudes toward cormorants indicate that cormorants' cultural carrying capacity is much lower than their biological carrying capacity (Conover, 2002; Wires & Cuthbert, 2006, p. 9). The greatest sources of conflict include cormorants' landscape transformative presence at nesting sites, their assumed impact on fishing industries, and their perceived impact on co-occurring colonial waterbirds (Weseloh et al., 2002; Wires & Cuthbert, 2010). Although irreversible tree damage occurs at nesting sites, demonstrating this species' impact on fishing industries is complex, and public perception of cormorants as competitors for sport fish is generally not supported by scientific evidence (Andrews, 2008; Duffy, 1995; Bedard, Nadeau, & Lepage, 1995; Koh et al. 2012; Hebert et al., 2005). Also, there is conflicting evidence regarding cormorants' impacts on other colonial nesting species, with the literature recommending site specific analysis (Cuthbert et al., 2002; Somers et al., 2011). Cormorants nesting in the Great Lakes illustrate the importance of identifying ecological interactions and ecological uncertainty as well as the importance of communicating scientific information to the public. Cormorants are native birds that fill a particular niche in the Great Lakes' ecosystem. In my research I strove to construct a scientifically based foundation on which to foster accurate perceptions regarding this controversial bird. This chapter is a result of my background research. 2 In the Great Lakes, the human-cormorant conflict has grown in recent years because of cormorant population expansion (Chastant, King, Weseloh, & Moore, 2014, p. 3; Latta & Faaborg, 2008). As of 2014, cormorant populations on the Great Lakes are expanding beyond previously published numbers, although there is some evidence that expansion may be stabilizing (Weseloh et al., 2002; Chastant et al., 2014). The cormorants' recent population success is largely due to legislative protection, the banning of DDT, and aquaculture expansion in wintering grounds (Cuthbert et al., 2002, p. 151; Boutin et al., 2011; Glahn et al., 1996; Nettleship & Duffy, 1995). On the Great Lakes, cormorant population numbers prior to the 20th century are unknown (Wires & Cuthbert, 2006), but documentation exists for range expansion into the Great Lakes early in the 20th century (Weseloh et al., 1995). Foster and Fraser (2013) suggest that cormorants are a foundation species because of their ability to transform the landscape of their nesting areas. Ecosystems are inherently dynamic, which means change is expected and intrinsic. In the Great Lakes, cormorants typically begin nesting in trees. As their nest building activities and acidic guano destroy the trees, the trees die and fall, and some of the colony begins to nest on the ground (Boutin et al., 2011). Rush, Dobbie, and Fisk (2013) suggest that the effects of altered nutrient levels from cormorant guano can be reduced if cormorants are managed in a low nest density range of ≤ 96 nests ha-1 (p. 306). Other studies indicate that there are non-negative aspects to cormorant habitat modification. A recent study on great cormorants (Phalacrocorax carbo) on a Stockholm archipelago indicated that arthropod diversity and abundance remained largely unaffected by cormorant density (Kolb, Palmborg, & Hamback 2013; Kolb et al., 2012). Also, even when great cormorant presence decreased species richness on a particular island, the resulting change in species composition increased overall archipelago diversity (Kolb et al., 2012). 3 A direct example of interspecies benefit from cormorant habitat modification concerns ground-nesting waterbirds (Leung, 2005; Hatch & Weseloh, 1999). While many migrating songbirds seek dense tree cover for protective resting places, ring-billed gulls (Larus delawarens), common terns (Sterna hirundo), herring gulls (Larus argentatus), and Caspian terns (Hydroprogne caspia) are ground nesting species that benefit from cormorant induced habitat modification (Leung, 2005; Hatch & Weseloh, 1999; Foster & Fraser, 2013). Increased presence of ground nesting birds may alter broader ecosystems by supporting terrestrial carnivore species such as coyotes (Foster & Fraser, 2013). This research suggests that cormorant-induced habitat modification can have positive outcomes. Demonstrating cormorants' impact on fishing industries is complex and involves a public perception that is generally not supported by scientific evidence (e.g. Wires et al. 2003; Duffy, 1995). The highly visible presence of this piscivorous waterbird allows for the perception of appropriately directed blame for depleted fish stocks (Duffy, 1995). Andrews, Fraser, and Weseloh (2012) investigated cormorant fish consumption and prey preference at Tommy Thompson Park, Toronto, Ontario. Although prey competition with sport fish was not considered, and results were biased toward chick diet sampling, researchers concluded that it was improbable that cormorant feeding directly affected the sport fishing industry. The alewife (Alosa pseudoharengus) and round goby (Neogobius melanostomus) are invasive fish species that are common in the Great Lakes and, since the cormorant is opportunistic, the majority of its diet in the Great Lakes is composed of these invasive species (Andrews, Fraser, & Weseloh, 2012; Hatch & Weseloh, 1999; Duffy, 1995). As of 2008, there were four published studies indicating that cormorants negatively impact sport fishing, and eighteen published studies indicating that cormorant predation impacts are negligible (Andrews 2008). Cormorants likely have only a negligible impact on fish populations because it is difficult to demonstrate scientifically that cormorant predation is additive rather than compensatory (Hatch & Weseloh, 1999; Wires et al. 2003). Assumed causation, when correlations between declines in fish populations and increases in cormorant populations are noted, has historically led to aggressive, unscientific management action (Dorr, 2010; Wires et al. 2003). At the population level, negative impacts of cormorants on commercially important fish are not scientifically supported (Duffy, 1995). The rising population of double-crested cormorants has increased the concern that other waterbird species are being displaced because of nest site competition and limited nesting materials. Though it has been reported that irreversible tree damage occurs at nesting sites in less than three years, the literature indicates that this does not correlate with negative impacts on other waterbird species (Cuthbert et al., 2002; Bedard et al., 1995; Koh et al. 2012; Hebert et al., 2005). The concern that cormorants negatively affect co-occurring colonial nesting waterbirds such as black-crowned night herons (Nycticorax nycticorax) and great blue herons (Ardea herodias) on a regional scale is not supported by the past 20 years of scientific documentation (Cuthbert et al., 2002). Research also indicates that the local impact of cormorants is limited (Cuthbert et al., 2002). Due to the inconsistent results attributed to variations in context and species involved, cormorant effects on other colonial waterbirds cannot be generalized as negative. Rather, documentation of interspecies interactions should be collected and results evaluated on a site specific basis to determine if interspecies impacts should factor into local cormorant policy (Cuthbert et al., 2002; Somers et al., 2011). Negative impacts of cormorants on both the Great Lakes' commercially valuable fish and on other waterbirds are not supported by scientific evidence (e.g., Andrews et al. 2012; Duffy, 5 1995; Cuthbert et al., 2002; Duffy 1995; Somers et al., 2011). An in-depth study of the literature indicates that the strong influence of anthropogenic factors on cormorant management comes from public outcry that is based primarily on perceived, rather than documented, impacts (Chastant et al., 2014). Unfortunately, many of the complexities and intricacies of this colonial waterbird are buried under negative folklore. Implications of this background research include the importance of conducting local studies on cormorant impacts as well as the importance of scientifically based cormorant management.