If you were bringing friends home to visit, you could show them the way. You know the landmarks—a big red house or a bus-stop sign. But what if you were swimming in the middle of the Atlantic Ocean? Could you still find your way home? A loggerhead turtle（海 龟）could.

According to Dr. Ken Lohmann, loggerheads have a magnetic（磁力的）sense based on Earth’s magnetic field. It helps them locate the best spots for finding food and their home beaches.

Scientists already know that several other animals, such as whales and honeybees, can detect（探测到）magnetic fields. The difference between them and loggerheads, however, is the way they learn to use their magnetic sense. Young whales and honeybees can learn from adults. Loggerheads are abandoned as eggs.

As newborn loggerheads have no adults to learn from, what helps them figure out how to use their magnetic sense? Lohmann thinks one of the cues was light on the sea.

Baby loggerheads hatch only at night. However, a small amount of light reflects off the ocean. The light makes that region brighter. Heading toward the light helps them get quickly out to sea, where they can find food. Lohmann tested whether newborn loggerheads use this light source to set their magnetic “compasses”（罗盘）. He and his team put some newborns in a water tank and recorded which way they swam. Around the tank, the scientists created a magnetic field that matched the Earth’s. They set a weak light to the east of the magnetic field. Then they let the newborns go.

At first, the newborns swam toward the light. After the scientists turned off the light, the turtles that had seen the light in the east always swam toward east. When the researchers reversed（颠倒）the magnetic field, these turtles turned around and swam toward the new “east”.

This and the follow-up experiments all showed that loggerheads use light from the outside world to set their magnetic “compasses” and then remember the “correct” direction. If a turtle hatches on a brightly-lit beach, that would damage its magnetic sense forever and make survival hard for the turtle.

Lohmann’s work has led others to protect the habitat of this endangered species. Yet many questions about these creatures remain unanswered, and researchers have a lot to study.

Most birds, in particular, exhibit some degree of patterns and colours. Australia’s zebra finch (斑胸草雀), for example, was so named because of the zebra-like black and white bars on its tail. But it also has many other colours and patterns, from a bright orange bill to fine white spots along its reddish-brown sides. It’s not uncommon to spot the bird in the drier parts of Australia.

We tend to suppose all individuals of that species have their spots and bars in the same places. Look closer yet we’ll see that the quantity and design of these patterns vary between individuals. And somehow a bird exhibits a more obvious feather variation. Occasionally, we see one that has larger than usual pale areas of feathers or, more rarely, has lost its normal patterning altogether.

Colouration and patterning in all animals are caused by a range of pigments (色素). Melanin (黑色素) is responsible for blacks and browns, and a lack of this pigment can cause a partial or total loss of an individual’s dark patterning. The two main terms that describe these abnormalities are albinism and leucism. Both conditions are genetic and both can lead to a very similar physical appearance. Leucism, however, causes a lack of the pigment cells that produce melanin. But albinism causes the production of melanin to be reduced or absent.

Can we distinguish between the two conditions without the help of a cellular biologist? Yes. Albino animals have fully unpigmented red eyes. Leucistic animals, on the other hand, never completely lose pigment from the eye, although they can have blue eyes due to a partial loss of pigment.

Why don’t we see more albino or leucistic birds? Because the lack of melanin reduces the strength and lastingness of the affected birds’ feathers, making them more easily broken. Additionally, the birds’ vision and hearing are negatively affected, making them less able to hunt. The brighter feathers and lack of patterning also make them easier for attackers to see.

Family dynamics in the animal kingdom are as different as the animals themselves. In the animal world, there are advantages to be gained from being part of an extended family.

Chimpanzees

Chimpanzees are the world’s largest living primates. These creatures are peace-loving and may live together for a lifetime. The dominant male has many wives who may stay with him for most of their lives, which can cause everyday conflicts. It is the male who settles the conflicts by a warning stare or hitting the back of the offenders’ heads.

Elephants

Females stick together in the elephant world, living in herds under a stateswoman. The experience and knowledge of this elder one, who may be 60-years-old, are of great benefit. She will remember, for example,the location of water holes and seasonal food supplies. In times of danger, the group bunches around the young and it is the stateswoman who decides whether to flee or confront the threat.

Lions

Lions are the only cats to live in a large family group, guarded by a pair of powerful males. Family life is relatively harmonious and baby lions may be fed by any mother with milk, so orphaned babies do not starve. Males live in the wilderness for some years before seeking their own pride by challenging resident males in a bloody battle. The male lion protects his pride from other males and enemies.

Ostriches (鸵鸟)

Ostriches travel in bands of 10-50 individuals, the most remarkable birds being the eight-foot-tall males. The largest birds in the world, ostriches cannot fly, but run fast. The wives of the male ostrich all put their eggs in the same nest. A primary female will then join the male to hatch (孵化) the eggs and she will push away other eggs on the outside to ensure her own are in the middle.