Natural Areas Inventory Update - Small Mammal Surveys

White Footed Mouse

Although 2007 was primarily an organizational one for the Natural Areas Inventory Project, we were able to sneak out into the woods to do some small mammal surveys before many of the critters hibernated for winter. These surveys were conducted under the expertise of Fiona Reid, associate of the Royal Ontario Museum and author and illustrator of the new Peterson Field Guide to Mammals of North America!

Small mammal surveys were done over the first 3 weeks of October at Silver Creek Conservation Area, the Credit Valley Conservation property surrounding Caledon Lakes and Rattray Marsh Conservation Area. Small mammals are seldom seen and when they are, the sighting is so fleeting that identification to species is often not possible. Some small mammal species must be measured for accurate species identifications, thus live-trapping is a necessity. We had help from 20 volunteers who were lucky enough to be able to view many of the Credit watershed's small mammals up close.

Tomahawk Trap

Three kinds of live traps were used - small ground traps, medium sized traps set on platforms fixed to tree trunks and pitfall traps sunk into the ground. Each trap type targets animals with different habits. The pitfall traps primarily target shrews. The tree traps target squirrels, including flying squirrels, which spend more time in the trees than on the ground. The ground traps target a variety of small, ground-dwelling mammals. Since most small mammals are most active during the night, the traps were closed during the day, then opened and baited in the late afternoon and checked for captures the next morning, after which they were closed again.

Short Tailed Weasel

We caught lots of mice, mostly white footed mice but also a couple of possible deer mice. The two species are very difficult to tell apart and a series of measurements and experience are needed to make an accurate identification. We also captured meadow voles, northern short-tailed shrews, masked shrews, smokey shrews, a long-tailed weasel, a short-tailed weasel, northern flying squirrels, chipmunks, red squirrels and grey squirrels. Rattray Marsh had so many grey squirrels (black-coated and grey coated are the same species) that we had a hard time keeping them out of the traps.

The Green Drake ( Ephemera guttulata )

Green Drake Spinner Courtesy of Heather Lynn

Green Drakes are insects of the Order Ephemeroptera (referring to their ephemeral, short-term existence as winged adults). Their first 2 years of life are spent as aquatic, three-tailed nymphs that burrow in soft, riverbed mud. In early June the nymph's "skin" splits along its back and it emerges both from its old skin and from the water to a new, but brief, lifestyle as a winged insect. Green Drake nymphs emerge from the water as winged "duns", with greenish-tinged wings and black and white bodies. When their populations are healthy, emergence happens en masse, in early June, starting around mid-day and continuing to peak in late evening. Green Drakes are large, for mayflies, and their size and abundance during emergence are attractive enough to coax even the largest trout from the river depths to rise for a feast (one fly fishing website refers to Green Drakes as "trout candy"). Fully emerged, the duns fly upstream, moult their skins one more time and become sexually mature "spinners", with striking black-veined wings and white bodies. Spinners are also known as "coffin flies". The spinners mate and the females drop their eggs back into the river at dusk to start a new life cycle. After two years as aquatic nymphs, the Green Drake's terrestrial, flying insect stage lasts only 2-3 days - ephemeral indeed. The spent spinner bodies float downstream providing trout with a second chance for a mayfly meal.

But all is not well with the Green Drake in the Credit watershed. Within the last ten years the Green Drake has been disappearing from the middle reaches of the Credit River and from Black Creek, where it was once abundant. Now, Green Drakes only emerged abundantly from a single tributary of Black Creek. Some older (second year) nymphs may still be found in the lower section of Black Creek but younger, first year nymphs have disappeared, ensuring that the cycle of population renewal will be broken. Henry Frania, of the Royal Ontario Museum , has been documenting the decline of the Green Drake in the Credit watershed and has been investigating possible reasons for it with transplant experiments, searches for nymphs and microscopic examination of dead nymphs. Frania's evidence points to increasing numbers of a toxic micro-organism living on the riverbed, which are being ingested by, and killing, the foraging nymphs. The kicker though, is that the micro-organism is natural, likely having always been a part of the ecosystem, but degradation of water quality and increased water temperature due to human development activities on adjacent uplands has favoured the micro-organism's increase and upset the natural balance of the aquatic ecosystem.

Frania's monitoring and research reveals similar problems in neighbouring watersheds. The Green Drake is declining in sections of the Rocky Saugeen River and while still abundant in the Beaver River , nymphs are under environmental stress there as well. The decline of an aquatic organism (or in this case, the aquatic phase of a species that bridges land and water environments) from the effects of human activities on land, soberly illustrates that the effects of habitat damage in one environment do not stop at that environment's boundary, but extend beyond to other parts of the ecosystem. The Green Drake may serve as an early harbinger of degradation in water quality - water that still looks clean and inviting may no longer be pristine.

The plight of the Green Drake reminds us that we need to work in an enlightened way to understand and protect biodiversity and ecosystem functions if we want to maintain healthy natural areas.