Grade Level: grade 5 - 8

Connection to other subjects: Science

Learning Objectives:  Students will read about the nesting behavior used by sea turtles and be able to explain how these behaviors are beneficial in the survival of a species.



bag of beans

stop watch

tally sheet

arribada article

question sheet


Teaching Time: 45 minutes



behavior conservation
instinct adaptation
predator prey
nocturnal diurnal



Only two species of marine turtles display a unique mass nesting behavior.  This behavior is known as an 'arribada'. This reproductive phenomenon was first observed by the scientific community in 1961. By producing large numbers of offspring most organisms like sea turtles can insure their survival even after predation occurs.


Students can discuss their findings with the class.  Have your students discuss ways to improve the disadvantages.

Class activity:


  1. Have students read the article and answer the questions provided at the end of this activity.
  2. Allow students sufficient time to discuss the advantages and disadvantages that sea turtles have by mass nesting.
  3. Have your students identify other organisms in nature that produce large numbers of offspring through mass nesting or mass births.


Arribada- Spanish term meaning arrival; a mass nesting behavior.

An arribada is a unique nesting phenomenon common to both the Olive ridley and the Kemp’s ridley sea turtle. The Olive ridley is endemic to the Pacific coasts of Mexico, Central America, and India.  It is known to be a nocturnal nester. The Kemp’s ridley is endemic to the Gulf of Mexico. It ranges from Galveston, Texas to Tampico, Mexico. Kemp’s ridley turtles display unique diurnal arribadas.

As they evolved, ridley sea turtles adopted a unique nesting behavior that increases their offspring’s chance of survival. They deposit more eggs in the sand than predators can consume. No other species of marine turtle uses this type of nesting behavior. Both species of ridley practice the phenomenon known as “predator swamping”.  “Predator swamping” can also be observed as hatchlings emerge from their nests in large numbers.  This behavior overwhelms the predators that wait to eat them on the beach. Predator swamping increases the odds of offspring surviving to adulthood and introduce that parent’s genetic information into the gene pool.

On unprotected beaches it is estimated that, for some species of marine turtles, only one out of one thousand or one in ten thousand hatchlings survive to adulthood. With current conservation efforts in place on nesting beaches, the current mathematical model now suggests that the survival rate is one out of three hundred.

In 1947 the first images of a Kemp’s ridley arribada were captured on film by Andres Herrera, a young Mexican engineer. It was estimated by some who have viewed the black and white footage that there were over 40,000 nesting Kemp’s ridley sea turtles on the beach that day. Unfortunately for the Kemp’s ridley this footage was put away and forgotten for over a decade. At that time the scientific community only knew of the Kemp’s ridley arribadas from rumors.  It wasn’t until 1960 that Dr Henry Hildebrand from the University of Corpus Christi viewed the film and then in 1961 presented that film at the annual meeting of the American Society of Ichthyologists and Herpetologists.  As you can imagine this film was an incredible discovery.  Two years later Dr. Hildebrand visited Rancho Nuevo, the site of the mass Kemp’s arribadas.  When he arrived in Rancho Nuevo the massive arribadas captured in Herrera’s film were no more.  The ridley nesting population had dwindled down to only 2,000 nesting Kemp's. By the early 1980’s, due to the continued illegal harvest of both females and their eggs, the Kemp’s ridley was on the verge of extinction. The remaining nesting ridley population had reached an all time low, only 300 nesting females.  In 1986, a joint bi-national recovery program by the governments of Mexico and the United States was created to save the Kemp’s ridley in the Gulf of Mexico.

Thanks to continued efforts by many caring individuals, the population of Kemp’s ridley in the Gulf of Mexico is on the rise.  As of 2006 12,000 Kemp’s nests have been protected along the Mexican coast and 100 recorded nests along the Texas coast.

Answer the following questions about the article you read.

  1. What is an arribada?
  1. What two species of marine turtles nest in large groups?
  1. What is one benefit of laying more eggs than predators can eat?
  1. What can be a potential problem for marine turtles that nest in large groups and nest in areas where poaching occurs?
  1. What other organisms will have multiple births in order to swamp predators?
  1. Thanks to current conservation efforts how many hatchlings survive to reach adulthood?
  1. In 1947 how many nesting Kemp’s ridleys were captured on the famous Herrera film?
  1. What has caused the decline of the Kemp’s in the Gulf of Mexico?

Name _______________________________________  Date _____________________

Advantages Of

Disadvantages Of

List 5 advantages and 5 disadvantages of mass nesting or mass births.

Class activity: The Bean Challenge 

Spill a bag of beans on a table and have your students pick up one bean at a time.  Give them a 5 second time frame to pick as many beans as they can.  Allow students some time to count their collected beans and then count what remains on the table. Repeat this activity with a 10 second, 15 second, 20 second, 25 second and 30 second period.  What remains on the table represents survival and what they have collected represents predation.

Time(Seconds) Number of beans collected Number of beans on table 
5 sec.
10 sec.
15 sec.
20 sec.
25 sec.
30 sec.
  1. How does the amount of time affect how many beans “hatchlings” you collected?
  1. How could a hatchling’s chances of surviving predation be increased?