Mississippi Valley Field Naturalists
March 26, 2008
Submitted by Pauline Donaldson
MVFN’s recent lecture explored why turtles outlived the dinosaurs but are now in trouble in Ontario
Photo: David Seburn discusses local populations of Blanding’s turtles with a carapace after MVFN lecture. Photo by Howard Robinson
Ecological consultant David Seburn was guest speaker March 20th for the 6th lecture in Mississippi Valley Field Naturalists (MVFN) series “Our Natural World: Conservation Challenges.” The lecture focused on Ontario’s turtles which Seburn describes as ‘endlessly fascinating’. As a species they have been around for so long they saw the dinosaurs go extinct! This is especially remarkable when one considers the relatively few species of turtles worldwide and only eight in Ontario.
The turtle’s shell, perhaps their best known and most unique feature, represents a serious biological limitation, Seburn explained. “They are enclosed in a little box so when they breathe they must compress their organs.” And when they need to pull in their head and limbs for defense, they have to hold their breath! Egg-laying is also a challenge. Not surprisingly the females tend to be larger than males to make room for eggs.
Seburn took the audience through the characteristics and distribution of Ontario’s eight turtle species and the conservation challenges they face. Interestingly, though loss and fragmentation of Ontario’s wetlands was one challenge highlighted, habitat protection did not dominate the discussion. Neither was the threat of global warming a major concern as we are at the northern limit for these reptiles’ successful egg hatching, so warmer temperatures could be beneficial. Why then, are six of Ontario’s eight turtles on the Canada’s ‘species at risk list’? As Seburn explained, Painted turtles and Snapping turtles are doing well. However the large Map turtle is of ‘special concern’ and the Spiny softshell, the Stinkpot, the Blanding’s and the Wood turtle are all considered ‘threatened’. The spotted turtle is in more serious trouble listed as ‘endangered’. It is rarely seen now.
Clues to the answer are the increasing adult mortality rate and the survival of eggs. Once turtles reach adulthood they can live a long time, and have the potential for a surprisingly long reproductive life combined with low rates of adult mortality. However, the natural success rate for eggs is so low that adult mortality must be kept at only 1-2% to maintain population stability. Unfortunately increasing adult mortality from road hazards has become a major problem when turtles travel on land to lay eggs or move to different food sources. The Blanding’s and Wood turtles are quite terrestrial and can travel 1-2 km to nest. Secondly, exacerbating a naturally low egg success rate is increasing predation from overpopulations of ‘subsidized’ predators such as raccoons in parks. Reaching more than 4 times regular rural numbers they can eat 100% of any turtle eggs in an area. Sadly sometimes the only warning sign a population is in trouble is it’s disappearance as all the adults eventually die off leaving no young.
Seburn made some suggestions to help conserve Ontario’s turtles. Short of closing down roads, municipalities can use drift fences or culverts to channel turtles across roads, and perhaps turtle crossing signs. Individuals can help turtles cross roads in the direction they were going (do not handle snapping turtles -lift them with a shovel). Large ‘ecopassages’ have been used in some places with great success in reducing mortality of a wide range of wildlife species. Recovery strategies for Ontario’s turtles also include research and population monitoring.
Info. from Seburn on identification and reporting turtle sightings has been posted on MVFN’s website (see Turtle Watch 2008 filed under Conservation). Turtle sightings can be reported locally to Mississippi Valley Conservation or to the Toronto Zoo Turtle Tally project by calling 416-392-5999.
‘Focus on Mammals’ by Glenn Desy (MNR) will be the last lecture in MVFN’s Conservation Challenges series, Thursday April 17th at 7:30 pm at the Almonte United Church Social Hall in Almonte. For more information, please contact Joyce Clinton at 613-257-4879 or visit MVFN’s website at www.mvfn.ca.