Visitor FAQs: Why do Painted Turtles and other semi-aquatic turtles lay their eggs on land?

One aspect of my profession as an interpretive naturalist is that I love is that there are never-ending opportunities to learn new things. And it's often the visitors of the nature center where I work that ask the most interesting questions.  Below is my response to a question a recent visitor asked. 

 A common sighting on a warm, sunny day in the Chicago region is Painted Turtles (Chrysemys picta) basking on a log in a shallow pond or slow-moving stream.  These stoic critters can appear rather lazy as they slouch in the sun, but as cold-blooded reptiles they must fire up their metabolism by absorbing heat from the sun.  An admirer who approaches too close to a basking turtle will witness an otherwise motionless creature plunge into the water and out of sight in a split-second.  

 But during the spring and fall, Painted Turtles are often encountered in rather unexpected places, such as along a trail, across a grassy field, and unfortunately along busy highways.  Are these turtles lost?  What are they doing so far away from the water?  Chances are, these land-wondering turtles are pregnant females looking for a suitable location to lay their eggs.  But why does an animal that spends 99% of its time in or near water decide to wander off, sometimes as much as 2 miles, to lay their eggs?  Why wouldn't they instead choose a site near the pond or in the water?  This was a provoking inquiry that one of my nature visitors recently brought to my attention.  

 Painted Turtles, like most species of turtles and tortoises, lay their eggs on land.  Turtle embryos are highly dependent on sunlight for their growth and their sexual development.   Turtles, like all reptiles, are ectothermic, or cold-blooded, and therefore must rely on an outside heat source, such as the sun, to engage their metabolism.  Much like a chicken-egg, turtle egg shells consist of a hard and dry calcium layer and do not hold up well under excessively moist or saturated conditions.   Furthermore, the ground generally warms much faster than water, allowing more suitable temperature grades for embryonic development.  

 Why Painted Turtles and other semi-aquatic turtles in the Chicago region travel so far from a body of water is unclear, but perhaps by doing so their eggs are less vulnerable to predation.  In either case, do not be surprised if you see a Painted Turtle strolling down a pathway with no apparent pond or lake in sight.  It might be time for them to lay some eggs!  
Figure 1: Painted Turtles and other semi-aquatic turtles spend much of the daytime basking in the sun, or in the case of these nature center turtles in captivity, under a heat-lamp.  
Figure 2: A recently hatched baby turtle.  Pregnant females will sometimes travel a mile or more from
the nearest body of water to lay eggs.  
References
The Science Behind Algonquin's Animals. (2005). Painted Turtle Research in Algonquin Provincial Park. Retrieved April 21, 2017, from http://www.sbaa.ca/projects.asp?cn=316

Comments

Post a Comment

Popular posts from this blog

Windy City Cactus: Eastern Prickly Pear Cactus

Image
When you think of Chicago, you probably don't think of sand dunes, prairies, or large oak trees.  Yet despite Chicago being the third largest city in the United States and heavily impacted by urban sprawl and industrial blight, there remains thousands of acres of greenspace with wetlands, open woods, sandy beaches...and some rather surprising flora. The pictures below were not shot in Arizona nor in Southwest California, but were in fact taken at the 63rd street beach on a recently restored sand dune near Hyde Park in Chicago, Illinois.  They are the eastern prickly pear cactus ( Opuntia humifusa ) . Figure 1:  Eastern prickly pear cactus, a native plant to the Chicago region and the only native cactus to the Great Lakes area.   The genus Opuntia is much more common out west where they have many different species, but in the Great Lakes and Midwest regions, the eastern prickly pear is the only native cactus.  It tends to be a little bit smaller than its western counterp
Read more

Virginia Pineapple? The fascinating family of Bromeliaceae

Image
Who hasn't tried pineapple before?  It always seems to end up in fruit salads at family reunions, there's always someone in the crowed ordering "Hawain pizza", and the grocery stores always seem stocked full with showy pineapples displaying their rough-textured, compartmentalized skin with bizarre green leaves on top (Photo A).  To most people living in temperate regions such as most of the lower 48 United States, pineapples are nothing short of exotic and unusual - and not like anything we have growing in the wild on our landscape...or do we? Photo A:  A pineapple grows wild along a woodland edge in a tropical park in  Ecuador, South America. Pineapples are in the family Bromeliacea, which includes a large group of mostly tropical plants that are primarily  epiphytes - plants that grow on top of other plants (see photo B). Photo B: Bromiliads, shown in the center of this photo, are a common group of tropical epiphytes throughout rain forests and
Read more

Natural Notes: Native Sunflowers

Image
September is the month of yellow, and for gardeners the easy-to-grow and popular choice of flower  is the Annual Sunflower ( Helianthus annuus ) which adorns garden borders and roadsides across the Chicago Region.  Numerous cultivars of this urban weed have been developed, and the source of commercial sunflowers and sunflower oil are derived from the Annual Sunflower (figure 1).  Figure 1:  Annual Sunflower growing  at the Taylor Street Farms community garden in Chicago.   But prior to European settlement, the Chicago region was largely absent of this tall and showy late-summer wildflower, whose range historically included the south-central United States into the plains and grasslands just to the east of the Rocky Mountains.  Instead, the prairie landscape of Northern Illinois would have been adorned with several species of native sunflowers and sunflower-like plants (figure 2).  Figure 2:  Although virtually absent of the notorious Annual Sunflower, the prairie landscape of N
Read more