The tiny hunter
Although Walker graduated with a degree in medicine, he walked the halls of the Toronto General Hospital for barely a year before realizing that he was better suited to walking in the woods. While field research makes obvious sense to biologists now, Walker was among the first of a new breed of scientists who made it essential to their work. “He certainly was a field naturalist,” remembers Bruce Falls, a former student of Walker’s and now himself an emeritus professor of zoology at the University of Toronto. “E.M. [Walker] was an outdoor person, basically. I think he felt his work was there.”
Although Ontario’s first endangered dragonfly is not especially distinctive, Walker had a soft spot for clubtails: their appearance and behaviours – including an enchanting habit of short, shimmering flights – “all combine to leave a characteristic impression on the mind of the observer,” he remarked. Rapids clubtail males dance brief forays over rippling rapids, hunting from exposed river rocks. Females are more elusive, flying farther afield and returning to the rivers only to breed.
It is the rivers, say scientists, which pose the problem. Like other dragonflies and damselflies, rapids clubtails survive just a few weeks as adults (in June), but during their larval life they spend as much as two years underwater. Although no one knows for sure, the species’ dwindling population appears linked to changes in the river home of the nymphs.
“The rivers in southern Ontario are not what they once were,” says Colin Jones, a zoologist with the Natural Heritage Information Centre of the Ontario Ministry of Natural Resources (MNR). “The very fact that [the Credit and Humber rivers] are now ‘urban’ rivers is probably the main reason why rapids clubtail may now be extirpated from the Credit and why the population on the Humber has apparently declined.”
Urban development has transformed the chemistry and even the temperature of the water, says Jones. Salty runoff from roads, for instance, threatens dragonflies and other water creatures with chloride poisoning. Erosion controls have changed the sediment pools critical to nymphs. In addition, invading or introduced species – the round goby and brown and rainbow trout, for example – have brought along a fearsome appetite for young riverine dragonflies.
The vanishing
Paul Pratt has made a hobby of tracking dragonfly “cold cases.” A naturalist with Windsor’s Ojibway Nature Centre, Pratt looks for place names in historic dragonfly and damselfly records and visits the sites to see what species are still there. So far, the results of his investigations are not good. “A lot of species … have either totally disappeared or haven’t been seen in 20 or 50 years,” he says.
Scientists agree that many dragonfly populations around the province are in trouble, but the insects can be affected by such a variety of factors that pinpointing the problem is difficult. Dragonflies and damselflies – which divide their time between a long larval life underwater (buried or hidden at the bottom of ponds and streams) and a brief adult life on land – are sensitive to aquatic pollution but also to deforestation, development and other changes taking place ashore.
Water quality is the most frequently named factor affecting populations. For instance, a 2001 study exploring the disappearance of midland clubtail dragonflies from Lake Erie after 1960 blames pollution and related changes that depleted oxygen in the water. Similarly, the now-endangered rapids clubtail may have been affected by river water contamination from road salt, fertilizer and leaching agricultural pesticides, says biologist Allan Harris.
Other waterborne threats to dragonfly nymphs include invasive species, such as predatory round gobies and even zebra mussels that colonize on the outer shell of living larvae and often kill them. Dams, weirs and shoreline barriers also change water flow and transform the sediment pools on which many nymphs rely.
On land, dragonflies in southern Ontario are perhaps most affected by development and land-use changes, says Harris. The loss of woodlands to farms and housing means many dragonfly adults are without cover from predators. Agricultural spraying may also be a factor. Scientific attention has recently focused on farming-related insect declines to help explain the plummeting numbers of Ontario’s insect-eating birds, such as common nighthawks and purple martins.
Clearly, the perils affecting dragonflies and damselflies are many. Although research can help isolate some of the reasons for declines in dragonfly numbers, finding a single cause and a single solution may simply not be possible. Says Harris. “Often, there’s no real smoking gun.”
P.C.
The human-induced environmental harm that threatens the rapids clubtail affects other species as well. Biologists blame those same changes in the Credit River for obliterating the endangered redside dace from many parts of its former range there. In recent years, once-teeming populations of green drake mayflies on the Credit (as well as on other southern Ontario rivers) have also plummeted (see “The vanishing”, page 21).
“We should be paying attention to this,” says Jones. “It’s like the canary in the coal mine. If these negative things are happening to these species, then what kinds of negative things are happening to other species, and what does that mean to us?”
MNR maintains records for Ontario’s 171 dragonflies and damselflies but “pays attention” to 60, tracking their populations carefully. These animals are not all in decline, but are – and in some cases may always have been – uncommon. Although the rapids clubtail is the only officially listed endangered species among the dragonflies and damselflies in the province, almost one in four species in this group is ranked as “critically imperilled” or “imperilled” because of its small or dwindling numbers. For many of these species, says Jones, COSEWIC has recently finished, or is about to begin, evaluating their at-risk status. In other words, more Ontario dragonflies and damselflies are likely to join the “endangered” club soon.
If there is a bright side to this distressing news, it comes via Ontario’s 2007 Endangered Species Act. Under the legislation, which generally has met with acclaim, dragonflies designated as endangered are not only protected directly, but also have their habitat sheltered from further damage or destruction. The law also requires that the government develop strategies to help troubled species recover.
“The good thing is that the dragonfly is recognized as being in trouble and a recovery strategy has to be developed,” says Anne Bell, senior director of conservation and education with Ontario Nature. “The listing ensures that attention will be paid and people will be putting their minds to doing something. It’s a very important driver for action.”
A draft of a recovery plan for the rapids clubtail is expected by September 10, 2010 – one year after the species was designated as endangered. Once the plan is finalized, the Ontario government will then have nine months to respond to the strategy outlining concrete plans to bring the species back from the brink. It’s too early to speculate what the plans might include, says MNR species-at-risk biologist Anita Imrie. Recovery strategies include various measures to address known threats and must recommend an area (or areas) to be protected through a habitat regulation.
Meanwhile, dragonfly and damselfly aficionados can hope the species and habitat protections that already apply under the law will be enough to keep populations from declining further. And, Imrie points out, independent efforts to improve habitat for the dragonflies are now eligible for support from the province’s Species at Risk Stewardship Fund.
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