A potential advantage of group movement in animals is increased locomotion efficiency. This implies a reduced energetic cost for individuals that occur in larger groups such as herds, flocks and schools. When chelonian hatchlings hatch in the underground nest with finite energy for their post-hatching dispersal phase, they face the challenge of minimizing energetic expenditure while escaping the nest. The term 'social facilitation' has been used to describe the combined digging effort of sea turtle hatchlings during nest escape. Given that in a normal clutch, a substantial part of the energy reserve within the residual yolk is used by hatchlings in the digging out process, a decreased cohort size may reduce the energy reserve available to cross the beach and sustain the initial swimming frenzy. This hypothesis was experimentally tested by varying cohort size in hatchling green turtles (Chelonia mydas) and measuring energy expenditure during the nest escape process using open-flow respirometry. The energetic cost of escaping through 40 cm of sand was calculated to vary between 4.4 and 28.3 kJ per individual, the cost decreasing as the number of individuals in the cohort increased. This represents 11-68% of the energy contained in a hatchling's residual yolk at hatching. The reduced energetic cost associated with large cohorts resulted from both a lower metabolic rate per individual and a shortened nest escape time. We conclude that synchronous digging activity of many hatchlings during nest escape evolved not only to facilitate rapid nest emergence but also to reduce the energetic cost to individuals.

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We present the first data collected on the genetic mating system of the hawksbill turtle Eretmochelys imbricata, the only marine turtle not studied to date. We examined paternity within 12 egg clutches from ten female hawksbill turtles from Sabah Turtle Islands, Malaysia. A total of 375 hatchlings were analysed using five microsatellite markers. Results demonstrated that clutches from two out of ten females were sired by multiple males (maximum of two). Although at a low frequency, observation of multiple paternity indicates that hawksbill turtles exhibit the same genetic mating system (polyandry) as observed for other species of marine turtles. Consistent paternity across multiple clutches laid by individual females in one breeding season supports the hypothesis that sperm are stored from mating prior to nesting and are then used to fertilize all subsequent clutches of eggs that season.Peer reviewe

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