Turtle Nesting Beach Design

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Nesting Areas
Review of Existing Knowledge
Constructing Artificial Turtle Nests
Literature

Nesting Areas

Review of Existing Knowledge

Moisture
The porous shelled eggs of many North American turtles exchange water with the environment inside their nests. Eggs in nests within moist soils consequently absorb water over the course of incubation, while eggs within drier soils typically lose water. The availability of water during incubation influences incubation time, hatchling size, locomotion speed and body composition. Embryos with access to more water (in relatively moist nest areas) will consume more of their residual yolk, have a longer incubation time, greater body size at hatching, increased locomotive performance and greater body hydration. Larger hatchlings may have a superior ability to avoid predation, but smaller hatchlings possess a larger reserve of energy in the form of residual yolk that could help support them over winter. While smaller turtles may have more energy reserves to draw from while overwintering, they do not have the potential to grow rapidly and overtake larger conspecifics.


Temperature
As with moisture, incubation temperature has been shown to affect hatchling size, growth rate and other characteristics. Incubation success is temperature dependent. Turtles have a range of temperature tolerance, outside which they experience abnormalities or mortality. The sex of some turtles is also determined by incubation temperature. Eggs incubated at higher temperatures within their tolerance range will produce females, while eggs incubated at lower temperatures will produce males. Both temperature and moisture influence the length of incubation, although temperature is more important in this factor than moisture. Generally, incubation length of turtle eggs is shorter at higher, female producing temperatures than at lower, male producing temperatures.

Turtle Species	Sex Determination and Egg Incubation Temperature
Snapping	20°C females 21-22°C male and female 23-24°C males 29-31°C females
Spiny Softshell	Sex determination not temperature dependent
Musk	25°C males 28°C+ females
Spotted	22.5-27°C males 30°C females
Wood	Sex determination not temperature dependent
Blanding's	22.5-26°C males 30-31°C females
Painted	20°C males and females 22-27°C males 30-32°C females
Map	25°C males 30°C+ females

Canopy cover
Canopy cover around turtle nests is negatively correlated with nest temperature, so that nests with more vegetative cover experience cooler temperatures. Nest temperatures in turn affect incubation success, hatchling sex and other characteristics (See above). One known cause of developmental failure is the selection of nest sites with reduced or absent solarization (closed canopy) that result in low temperatures. Sites with more shade, and lower temperatures, could prolong development to an extent that embryos would fail to hatch before fall freeze. Typically, nests are found in predominantly open, exposed sites with minimal vegetative cover. These exposed sites have increased nest success compared to those with more cover. However, nearby grasses and ground cover increase the probability of hatchling survival.


Substrate
Moist, well-drained, loose substrates make digging easier, promote air circulation, provide moisture and are less likely to harden like clay soils. Dry substrates have been shown to cause total or partial failure of nests. Firstly, substrates that are too dry will not supply the eggs with enough water. Secondly, dry substrates may collapse into the nest cavity where some of the eggs will remain uncovered or be broken during covering. Turtles require a balance between substrates that are too wet and substrates that are too dry, and may select sites with different substrates depending on climatic conditions of the year. Friable, granular silt loam soils and sand-gravel mixes are the best substrates.

Orientation/Slope Preferred nest sites have maximum sun exposure and are therefore south, south-west facing.

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.



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.



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):


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

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

LITERATURE

Congdon, J.D., Nagle, R.D., Kinney, O.M., Osentoski, M., Avery, H.W., van Loben Sels, R.C. and D.W. Tinkle. 2000. Nesting ecology and embryo mortality: Implications for hatchling success and demography of Blanding's turtles (Emydoidea blandingii). Chelonian Conservation and Biology 3(4): 569-579.

Ernst, C.H., Lovich, J.E. and R.W. Barbour. 1994. Turtles of the United States and Canada. Smithsonian Institution Press, Washington and London.

Finkler, M.S., Bowen, J.T., Christman, T.M. and A.D. Renshaw. 2002. Effects of hydric conditions during incubation on body size and triglyceride reserves of overwintering hatchling snapping turtles (Chelydra serpentina). Copeia (2): 504-510.

Gutzke, W.H.N. and G.C. Packard. 1987. The influence of temperature on eggs and hatchlings of Blanding's turtles, Emydoidea blandingii. Journal of herpetology 21(2): 161-163.

Kiviat, E., Stevens, G., Munger, K.L., Heady, L.T., Hoeger, S., Petokas, P.J. and R. Brauman. 2004. Blanding's turtle response to wetland and upland habitat construction. IN: Conservation and Ecology of Turtles of the Mid-Atlantic Region: A Symposium. Swarth, C.W., Roosenburg, W.M. and E. Kiviat (Eds). 2004. Bibliomania!, Salt Lake City, Utah.

Kolbe, J.J. and F.J.Janzen. 2002. Impact of nest-site selection on nest success and nest temperature in natural and disturbed habitats. Ecology 83(1): 269-281.

Packard, G.C. and M.J. Packard. 1987. Influence of moisture, temperature and substrate on snapping turtle eggs and embryos. Ecology 68(4): 983-993.

Packard, G.C. and M.J. Packard. 2002. Wetness of the nest environment influences cardiac development pre- and post-natal snapping turtles (Chelydra serpentina). Comparative Biochemistry and Physiology Part A. 132: 905-912.

Rhen, T. and J.W. Lang. 1995. Phenotypic plasticity for growth in the common snapping turtle: Effects of incubation temperature, clutch, and their interaction. The American Naturalist 146(5): 726-747.