Can kangaroos delay or prevent pregnancy when times are hard?

Answer 1

Many of the 60 or more species of kangaroos can "pause" their pregnancy. This is called "embryonic diapause". The mother kangaroo spends most of her adult life pregnant, but in drought times, she has the ability to indefinitely "freeze" the development of the young embryo until food sources are replenished. This is one of the kangaroo's adaptations for living in a harsh country like Australia.

Answer 2

This is an automatic response to the external conditions, and is known as embryonic diapause.

Most kangaroos are able to breed all year round, but conditions will determine how often they reproduce. Female kangaroos can often be in a state of almost permanent pregnancy, with an embryo "suspended" until the mother's body is ready to release it - whether that be when another joey is sufficiently weaned, or feeding conditions have improved.

Embryonic diapause works by the embryo developing until the blastocyst stage, which is the stage just before implantation f the embryo occurs, and then waiting for particular signals from the uterus which will basically "give the go-ahead" for their further development. If these signals are not sent by the uterus, development of the embryo will stop. The signals are in response to environmental conditions, i.e.. whether there is enough food to support more joeys, or to the mother's own condition, i.e. is she healthy enough to support the growth of another joey, and is the previous joey ready to be weaned? put simply, these signals are sent by the mother's body, according to what her hormones are doing.