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Turtle Nesting Areas

Nesting Areas Existing Knowledge Constructing Artificial Turtle Nests


Constructing Artificial Turtle Nests

The following characteristics of preferred nesting sites should be considered when constructing artificial nests:

  • South, south-west facing (maximum sun exposure)
  • Moist, well-drained substrate
  • Fairly loose soils- sand/gravel
  • Minimal vegetation cover
  • Nearby ground vegetation for hatchling protection
  • Avoid linear landscape features (i.e. roads, shorelines, paths) that may be used by predators
  • Construct more then one nesting area.
Substrate is likely one of the most influential characteristics in turtle nesting. Along with site location, substrate influences both nest moisture and temperature. Turtles and their eggs have a range of temperature and moisture tolerance, outside which they experience abnormalities or mortality. Their nests require a balance between a substrate that is too wet and a substrate that is too dry. Eggs that sit in water or saturated substrate will drown or develop mold. However, substrates that are too dry will not supply the eggs with enough water. The substrate must also allow air circulation and be loose enough for the female to dig the nest and for hatchlings to dig their way out. While turtles seem to prefer nesting sites with moist, well-drained soils, they may select sites with different substrates depending on climatic conditions of the year. It is important to provide variation in your nesting sites and offer nesting turtles many options. Try different substrates, mixtures of substrates and different locations. We know that turtles have opportunistically nested in substrates created for other purposes such ploughed farm fields, lawns and flower beds to coal slag, piles of sand, woodchips and roadside shoulders! Constructing more than one nesting area is important in your design as they will provide micro-climate variation, reduce the likelihood that vegetation will cover the site and reduce predator saturation of nesting sites.

( Dave Ireland) ( Bob Johnson)
Some turtles lay eggs in loose gravel similar to roadside shoulders


The type and size of the substrate particles will affect air space, temperature and moisture level. For soil, there are three size fractions: sand, silt and clay. Loam is some combination of all three.

Particle Size Properties
Clay Less than 0.004 mm Holds water, hard
Silt 0.004 to 0.06 mm Behaves more like small sand grains than clay
Sand 0.06 to 2 mm Well-aerated and well-drained, loose structure. Fine sand less aerated and drained than course sand
Gravel 2+ mm Well-aerated and well-drained, loose structure


Suggested artificial turtle nest substrates: Gravel, sand, sandy loam (better water retention than fine sand), disturbed soil, woodchips, dark/light substrate colours (dark will absorb light and provide more warmth) and replicas of gravel road margins.


Often turtles are attracted to the warmth of compost,
similar to this woodchip-type substrate


Many turtles dig their nests along roadsides, in the road shoulder. The following is a description of the road shoulder gravel used by the Ministry of Transportation Ontario (MTO):

MTO Road Shoulder Gravel
(used over the granular or sand subbase)

Crushed rock composed of hard fragments produced from rock formations or boulders, or a mixture of crushed gravel, sand and fines composed of hard particles produced from naturally formed deposits, or crushed slag produced from iron blast furnace or nickel slag. May also consist of a blend of natural aggregates, reclaimed Portland cement concrete and reclaimed asphalt pavement material.

Sieve Designation Percentage Passing Through Sieve Designation*
Road Shoulder
Granular 'A'/'M'
Subbase
150 mm N/A 100
37.5 mm N/A N/A
26.5 mm 100 50-100
19 mm 85-100 N/A
13.2 mm 65-95 N/A
9.5 mm 50-83 N/A
4.75 mm 35-60 20-100
1.18 mm 15-40 10-100
300 m 5-22 5-95
150 m N/A 2-65
75 m 2-10 0-25

* A sample of known weight is passed through a set of sieves of known
mesh sizes. The sieves are arranged in decreasing mesh diameters. The
sieves are vibrated for a period of time and the particles sort through the sieves.
The amount of substrate retained on each sieve is measured and converted into a percentage of the total sample.


While open, exposed sites are preferred, some low ground vegetation may to help decrease predation of hatchlings. However, you will have to keep the vegetation from becoming too dense or too close to the nest site - active vegetation maintenance may be necessary. Landscape filter cloth, buried well below nesting depth (12") can be placed to prevent vegetation from establishing at the nest site. The presence of vegetation will also help stabilize substrates and provide erosion control. In natural systems, floods and erosion provide an ongoing supply of exposed soils available across the landscape as older, or more stable, sites become more vegetated.

It may be necessary to protect nests with a wire predator exclosures that cover the nest and extend into the ground around the nesting area. Wire mesh must be large enough (2" x 3") to a low hatchlings to pass though after they emerge from the ground. If necessary, predator guards may be removed 14 days fter egg laying as most nest predation occurs in the week After egg laying.

Unfortunately, there is not a lot of detailed scientific data on the specifics of turtle nesting sites. It is suggested that you provide variation in your nesting sites and offer nesting turtles a mosaic of options. If you don't know where to start, use data loggers and collect information (temperature, moisture, canopy cover, soil properties) of known nesting sites and try to replicate them.

Implement a monitoring program. Note where turtles are nesting (and where they are not nesting) and collect as much information about these sites as possible. Collect soil samples and analyze them for moisture content, texture (water potential) and other properties. For nest sites, monitor nest temperature, moisture, hatchling success and predation rate. Gathering and sharing this information will help to identify common preferred nest site characteristics

The cost of implementing an artificial turtle nest project will vary according to the project design. Materials (i.e., substrate, vegetation, filter cloth), equipment (i.e., backhoe, temperature/moisture analysis) and manpower should be factored into your budget.

Examples of Potential Costs
Equipment
Backhoe, cat rental $275 per day
Landscape filter cloth $12 per 3'x50' roll
Substrate
Pea gravel $35 per cu.yd.
Granular 'A' Gravel $32 per cu.yd.
Mulch $40-55 per cu.yd.
Landscape soil (topsoil/sand) $20 per cu.yd.
Sand $20 per cu.yd.
Topsoil $20-30 per cu.yd.
Vegetation
Groundcover $3-6 per 4" pot
Shrubs $20 per 2 gal
Vines $25 per 2 gal
Grasses/Cattails/Rushes $5-15 per 4" pot

From time to time, eggs must be moved due to:
  • Accidental uncovering
  • Construction on the nest area
  • Nesting on roadsides
  • Predator digging into the nest
Important notes about nest relocation and moving eggs:
  • Eggs should only be moved to a nearby location and left in the wild.
  • Carefully lift each egg without rotating, rolling or shaking it. Always keep the top of the egg oriented to the top.
  • Place in an old egg tray or nestle into sand/soil so that the eggs do not roll.
  • Transport to a nearby nest area that is a similar distance from the water body, has a similar orientation to the sun, and a similar substrate material and moisture.
  • Dig a hole to the same depth as the original nest (~8-10") with a wider bottom than the top (i.e. flask shaped).
  • Carefully place eggs into hole with the eggs 'top' upwards in the nest.
  • Lightly cover eggs with soil/sand and then fill in rest of hole
  • It may be necessary to cover the nest with a wire mesh predator guard.
Most Ontario turtle eggs will hatch in 60-90 days, although painted turtles often hatch and overwinter in their nest, emerging the following spring.

Note: turtles have an attachment to previously used nesting areas and are likely to avoid using other sites as long as their traditional ones remain. Turtles will cross seemingly good nesting areas to reach sites used in previous years. It is not surprising then that female turtles cross artificial or constructed nesting areas to reach the traditional egg laying sites. It may take several years for new females to select your site or for conditions to mat

Predation of turtle eggs is very common Dave Ireland Critical habitat for turtles includes wetlands and adjacent terrestrial landscapes Dave Ireland

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