Sea turtles’ eggs are laid at night to minimize the likelihood of their discovery by predators, and the offspring, when ready to emerge from their eggshells and dig their way out of the sand, hatch at night for the same reason. Since the offspring are especially vulnerable immediately after hatching, it is vital for them to get to the sea as soon as possible. Turtle hatchlings use a number of cues to tell them where the sea is.

The most important cue seems to be light. The night sky is usually brightest over the sea. Cover a turtle hatchling’s eyes, and it cannot find the sea even if there is other information available, such as a downward slope of the sand toward the water’s edge. The hatchlings respond to light cues covering a vertical range of only about 30°above the horizon or, depending on the species, even less. Responding only to lights that are close to the horizon decreases the risk that hatchlings will become confused. They seem less attracted to yellow light than to other colors—loggerhead turtles show an aversion to yellow light—and this preference may keep them from becoming disoriented by the rising Sun.

It is usually safest to have more than one internal compass, and hatchlings seem to be guided by more than light alone. They steer away from sand dunes and vegetation. Possibly these objects merely block light behind them that might mislead turtle hatchlings about where the sea is, but it is also possible that turtles are sensitive to the shape of such objects and process these shapes as signals that the sea is located in some other direction. Such reinforcing cues, however, are not enough to guide hatchlings away from the artificial lights that now burn on many a beach environment. Artificial lighting is often strong enough to completely overcome the signals a hatchling sea turtle is programmed to recognize. Artificial light, if it is bright enough, becomes a stimulus so powerful that the hatchlings respond to nothing else, crawling toward it from hundreds of meters away.

If all goes well and the hatchlings scramble over the sand in the right direction, avoid their enemies, and reach the surf, a new set of orienting mechanisms takes over. As soon as they are afloat, the hatchlings begin to swim at something over 1.5 kilometers per hour. They dive into the path of the wave undertow, where the receding waters sweep them outward, away from the beach. When they surface again, the head for open sea. This time, they are guided not by sight but apparently exclusively by the direction of the incoming waves. Experiments with loggerheads, greens, and leatherbacks have shown that hatchlings swim toward approaching waves; but if the sea is calm, they swim randomly or in circles. Under experimental conditions, hatchlings will swim into the waves even if doing so sends them back to the beach again.

The farther a hatchling gets from shore, the less reliable wave direction becomes as a pointer to the open sea. Researchers have shown that hatchling green sea turtles released from a hatchery in Borneo, East Malaysia, are able to navigate around small islands and keep swimming offshore, even when there are few waves to guide them. They may be relying on yet another internal compass this time oriented to Earth’s magnetic field. Recent experiments suggest that leatherback and olive ridley hatchlings “switch on” their geomagnetic compass almost as soon as they are out of the nest. Though the hatchlings position themselves geomagnetically as soon as they leave the nest and appear to be able to use that position as a reference point, they will not follow it automatically if other cues, such as light and sound, are available. Hatchlings find their geomagnetic compass useful only after they have already been able to determine the direction they should swim. A simple directional compass—one that always sent the turtles westward, for instance—would be useless if the open sea lay in some other direction. Therefore, a magnetic compass does not so much tell a hatchling turtle which way to go as keep it on course once it has determined the direction it should swim from some other cue.

晚上放置海龟蛋是为了尽量减少捕食者发现它们的可能性，而当它们准备从蛋壳中出来并挖出沙子时，它们的后代也同样会在夜里孵化出来。由于幼崽在孵化后会特别容易受到伤害，因此它们需要尽快到达海上。海龟幼仔会使用一些线索告诉它们海洋在哪里。 最重要的线索似乎是光。夜空通常在海上最亮。如果盖住龟龟的眼睛，即使有其他信息可用，也无法找到大海，例如沙坡向水边的斜坡。孵化后的幼龟会对光线的线索做出反应，对仅为地平线上方约30°的垂直范围的光线提示做出反应，根据不同的物种，甚至更少。只对接近地平线的光线做出反应，就会降低孵化幼虫对方向感到困惑的风险。它们看起来对黄光的吸引力会比对其他颜色的吸引力要小得多，如红海龟对黄色光线表示厌恶，而这种偏好可能使它们不会被升起的太阳迷失方向。 通常最安全的状态是有几种途径辨别方向，而且幼龟似乎不仅仅受光照的引导。它们也避开沙丘和植被。可能这些物体仅仅阻挡了它们后面的光线，可能会误导幼龟不知道哪里是大海，但也可能海龟对这些物体的形状很敏感，并将这些形状当作信号，表明海洋位于其他方向。然而，这种的强化提醒还不足以引导幼龟远离现在许多海滩燃烧的亮光。通常人工照明足够强大，可以完全使得海龟分不出这些编程识别的信号究竟是否是真正的。人造光如果足够亮的话，就会对幼龟造成强大的刺激，使得它们不会对其他任何物体产生反应，从几百米以外的地方爬向它。 如果一切顺利的话，幼龟在正确的方向上爬过沙子，避开它们的敌人，并到达冲浪地区，这样也就产生了一套新的导航方式。一旦它们漂浮起来，幼龟就会开始以每小时1.5公里的速度游泳。它们在海浪中游泳，在那里后退的海水将他们从海滩上冲走。而当再次浮出水面时，它们就发现自己就在海面上。这一次，它们不是被视觉所引导的，而是显然完全由入射波的方向所引导的。红海龟，果岭和棱皮龟的实验表明，幼龟会朝着接近海浪的方向游来游去;但如果海水风平浪静，他们会游得很随意或绕圈游泳。在实验条件下，即使这样做把幼体再次送往海滩，它们也会照样游向海浪。 幼龟离海岸越远，越不可靠的波浪方向就将变成了指向大海的指针。研究人员已经证明，在马来西亚东部婆罗洲的一个孵化基地，孵出的绿海龟能够在小岛屿周围导航，并在近海游泳，即使只有很少波浪能够引导它们时也是如此。他们可能依赖于另一个内部指南针，这次是指向地球磁场的。最近的实验表明，棱皮龟和头橄榄海龟在它们离开巢穴的时候就会“开启”它们的地磁罗盘。虽然幼龟在离开巢穴后立即就开始了地磁的位置，并且似乎能够将该位置用作参考点，但如果其它提示（例如光线和声音）可用，它们将不会自动跟踪它。只有在它们已经能够确定它们应该游泳的方向之后，幼崽才会发现它们的地磁罗盘有用。一个简单的方向指南针，例如总是把海龟往西的方向指引，如果是大海位于其它方向时，这将毫无用处。因此，一个磁罗盘并不会告诉一只刚孵化的海龟，一旦它确定了自己应该从其它线索游泳的方向，它应该继续前进。