Why do birds and mammals lay only a few young at a time?

Answer 1

These animals use two different methods of insuring that enough of their offspring survive to reach maturity and reproduce.

Most fish produce large numbers of offspring that are often left to fend for themselves.

Mammals care for and protect their young. They can have fewer offspring because the parents invest more time energy and often training to insure a higher survival

rate.

Realize that some fish care for their egg and offspring and some mammals care for their offspring for very little time, relying on increased maturity at birth to increase

survival rates.

Answer 2

The number of young produced (in a litter, or in general) by an animal has a large correspondence to the likelihood that any given young will survive until adulthood. An animal would not have just one young if it were very unlikely that this young would survive, and an animal would not have thousands of young if each one would very likely survive to adulthood (this would increase the population far too much). For example, frogs lay thousands of eggs at once, but only a few young will survive to adulthood. But a baby mammal is much more likely to survive until adulthood, so mammals tend to have fewer young. This correspondence is found within the class of mammals too. A female house mouse may produce more than 100 babies in her lifetime, but most will not survive. But a female chimpanzee typically only produces up to five or so babies, but each has a comparatively high likelihood of surviving until adulthood. The correpsondence is also found within the human species, as women in poorer countries tend to have more children than women in richer countries.

Answer 3

Mammals are better suited to protect their young than other vertebrates. Other vertebrates are less suited to protecting their offspring, so they need to have a much higher number of young to compensate for predation by other animals. The higher the number of offspring = the higher the chances of some of them making it. Mammals have evolved to more easily protect their young and care for them, therefore they have less offspring.

Answer 4

Other types of animals like frogs or insects have a lot of children because the odds are that not many of them will actually survive for very long. Mammals only have a few babies but protect them for a while so they dont just die right away

Answer 5

Birds and mammals and some reptiles have relatively few young, compared to some fish, reptiles and a lot of insects because they either produce large, semi independent young at birth (eg some lizards have 1 or 2 live young that often look eye wateringly large), or they have young that need intense, individual care, (eg humans), that may include 3, 5 years of being taught survival skills, (in humans, in the middle ages, you'd raise a daughter to 12, 15 years and then marry her off...) Generally, the larger, the more intelligent the animal, the longer and more intense the individual training investment. (eg elephants take years to raise their calves and also years teaching them where to find food and water in their yearly moves, following feed). Sharks are fish but they lay eggs singly, (and they are worth looking for on the Net), extraordinary, large, screw shaped eggs that are pushed into gaps in rocks. Simply put, rule of thumb, the more pregnancy time and nutrition, the more care a baby needs - the longer it's "childhood," the fewer the babies. The huge number of fish eggs spawned is the second biological survival pattern, where of 200 babies, perhaps one survives to breed successfully. The investment in each tiny egg is minimal. So, the greater investment on the mother's side, the more valuable the offspring, the fewer she will produce.

Answer 6

Mammals have any number between one and twelve or so offspring.