What has been learned about the turtles which nest on Bird Island                                    
 

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Please note that Bird Island owns the copyright to this material and that our data may not be published or cited in a publication without prior permission.  Data analysis reported in this web page was provided by Dr. Jeanne A. Mortimer. 

Hawksbill Turtle (Eretmochelys imbricata)

Nesting Season:
Peak nesting season for Hawksbills at Bird is during the period mid-October through mid-January.  But, in fact, there is a chance of seeing a nesting turtle during any month of the year.  Hawksbills in Seychelles (and elsewhere in the western Indian Ocean) nest in the daytime.  This makes them quite unique in the world.

Numbers of Females:
On average, Bird Islands hosts approximately 35 individual adult female hawksbill turtles each season.  Since the turtle study began in 1995, this figure has ranged from about 20 to 50 females, depending on the season.  Numbers of turtles naturally fluctuate from year to year.

Numbers of Egg Clutches Laid:
Each hawksbill, on average lays about 4 to 5 egg clutches.  The total number of egg clutches laid by hawksbills each year at Bird Island is about 145 - ranging from a recorded low of 80 to a high of 203. 

Numbers of Nesting Emergences:
Not every nesting emergence results in a successful egg laying.  For each egg clutch laid, the average female emerges 1.6 times.  In other words, in order to lay 4 or 5 egg clutches, the average female must emerge about 6 to 8 times.  The average annual total number of hawksbill nesting emergences at Bird Island has been about 225 - ranging from a recorded low of 124 to a high of 321. 

Tagging Efficiency: 
Approximately, half of all hawksbill nesting emergences are intercepted by the turtle research team on Bird. All turtles intercepted are tagged (if they arrive untagged) or have their tag numbers recorded if they are already tagged.  Not all nesting emergences are intercepted, but because individual turtles emerge to nest so many times during a single nesting season, almost every female hawksbill is tagged during the course of the nesting season at Bird Island.
 

Green Turtle (Chelonia mydas)

Nesting Season:
Peak nesting season for green turtles at Bird is during the period January to June.  But, in fact, green turtles nest during every month of the year.   Unlike the hawksbill, green turtles in Seychelles nest at night. 

Numbers of Females:
At most localities in the Indo-Pacific, the average green turtle lays about 5 egg clutches per season.  Based on this and the recorded total numbers of nesting emergences, there are an estimated 3 to 15 female green turtles nesting each year at Bird Island.  During the course of the nesting season, each of these animals can be expected to emerge onto the nesting beach about 6 to 8 times.

Numbers of Egg Clutches Laid:
The total annual number of egg clutches laid by green turtles at Bird Island is about 22 - ranging from a recorded low of 13 to a high of 58.  Like hawksbills, green turtles do not always nest successfully when they make a nesting emergence.  At Bird Island, the average green turtle emerges about 1.3 times for each egg clutch laid.

Numbers of Nesting Emergences:
The average total number of green turtle nesting emergences at Bird Island is about 31 - ranging from a recorded low of 14 to a high of 91.  Green turtle nesting activity can fluctuate greatly from year to year.  This is natural, and may be linked to climatic events such as El Nino.

Tagging Efficiency:
Because the green turtles nest at night and are relatively rare, it is difficult to intercept one on the beach.  Mostly we learn about them by studying their tracks on the beach.  To date, 5 female green turtles have been tagged at Bird Island. 

Results of Monitoring Program until end of 2004- 05 season 

 * 1995-1996 Programme commenced November 1996

Nesting Female Hawksbills Tagged