Nest Temperatures

 

Incubation Time

In 2017, N.E.S.T. volunteers began placing temperature data loggers in all of our sea turtle nests. In 2018 we upgraded our technology to Bluetooth capable data loggers whereby N.E.S.T. volunteers could download hourly temperature data directly from the nest to their cell phones for real time data analysis. We intend to collect temperature data on our nests for several years. Our goal is to explore how real life nest temperatures impact incubation times and the viability of embryos and hatchlings. We hope the temperature data we collect will help nest parents and other volunteers better manage nests and further engage beach goers and turtle lovers in our cause.

Volunteers locate 2018 Nest 5 in Corolla and place temperature datalogger in nest.

Volunteer holds cell phone over nest to download data from logger

As a starting point for our work, we looked at a number of scientific studies related to incubation temperatures of sea turtle nests. Researchers generally use constant incubation temperatures. We intend to compare real life situations where temperatures vary from hour to hour and day to day with the data gathered in those studies. Below is a brief summary of only some of the research on incubation temperatures for Atlantic loggerhead sea turtles.

  • Optimal constant nest incubation temperatures are generally around 83 to 88 degrees Fahrenheit i.e. mid-range temperatures.
  • Constant nest temperatures equal to or above 89 to 91 degrees Fahrenheit generally mean embryos do not hatch or hatch but do not survive
  • Constant nest temperatures of 87.8 degrees Fahrenheit produced hatchlings with poor righting response times but normal swimming and crawl speeds.
  • Constant nest temperatures equal to or below 75 to 77 degrees Fahrenheit generally mean embryos do not hatch
  • Incubation temperatures  at or below a constant 80.6 degrees Fahrenheit produce hatchlings with decreased vigor, poor righting response times, slow crawl speeds, and overall poorer swimming ability
  • The variation of temperatures in natural nests may alter some of these effects
  • The metabolic heating (from growth of embryos) that occurs in nests especially during the last half of incubation may alter these impacts.

Graph of temperature data downloaded from nest

Temperature-dependent Sex Determination (TSD)

Incubation temperatures are also important because the sex of a sea turtle is determined by the temperature of the nest during the second trimester of embryonic maturation. This is called temperature-dependent sex determination (TSD) and is common in reptiles. In our area for loggerhead sea turtles, the temperature where 50% of the embryos will be male and 50% will be female is around 84.6˚F. This is called the pivotal temperature.  A mean temperature of 86.9˚F will result in 100% females and a mean temperature of 81.5˚F. will result in 100% males. As our climate changes and oceans warm, colder northern breeding grounds such as those covered by N.E.S.T. OBX are important to providing sufficient numbers of male hatchlings to sustain and grow overall sea turtle populations.

The chart above shows each 2019 nest where temperatures were logged from within the nest and the estimated gender make-up of the nest using Mrosovsky’s (1988) model for sex determination.

The above chart shows the estimated make up of male/female hatchlings in our northern Outer Banks nests. We utilized 2nd trimester mean temperature data collected from inside each of our successfully hatched nests between 2017- 2019 and plotted it using Mrosovsky (1988) model for sex determination.

This graph displays the same information from the above chart but breaks it out specifically by each nest. Every blue dot represents a successful nest between 2017 – 2019 in our area and shows the Average Mid-Trimester Temperature and estimated % of female hatchlings it produced.