-No common theme to parental behavior among vertebrates or mammals.
1. Biparental vs. uniparental
>90% of birds are biparental
>90% of mammals are uniparental
In 100% of mammals, the female is involved in parental care.
2. Precocial vs. atricial young
Precocial: Offspring the are capable of moving independently, maintaining their
body temperature, hearing, and seeing shortly after birth.
Ex. Horses, cattle, elephants, guinea pigs
Atricial: Offspring that are very immature. They may be blind, deaf, furless, unable
to maintain body temperature, unable to urinate and defecate, etc.
Ex. Rats, mice, hamsters, dogs, cats
Most primates aren’t clearly precocial or atricial. They can hear, see, maintain their
body temperatures, urinate and defecate, but they can’t fend for themselves at all.
3. Continuous vs. intermittent care
Some species spend very little time on parental care.
Tree shrews deposit their offspring in an arboreal nest and visit once every 48 hrs.
Rabbits spend about 3 minutes a day with their babies, ‘inject’ some milk and then
Other species (e.g. primates) are in nearly continuous contact with their infacts.
Rat pregnancy and lactation
1. A rat pregnancy lasts 22-23 days with the day after mating counting as day 1.
2. The blastocysts implant in the uterine wall around day 5, after which it becomes difficult
to interrupt pregnancy.
3. The mom begins to care for her pups as they emerge from the birth canal.
4. Initially, the pups depend on their mom for everything.
5. By day 10, they have fur and can see, hear, and move around.
6. They begin to eat “grown-up food” around day 12, and are weaned completely by day 25.
Rats and a number of other species exhibit a postpartum estrus.
1. Hormonal changes just before parturition are similar to those just prior to ovulation in
2. Female rats mate and ovulate within 48 hours of parturition. If they copulate with a male,
they become pregnant (again).
3. Implantation of the blastocysts may be delayed 5-6 days, but the females are pregnant and
lactating at the same time.
4. This puts enormous energy demands on the mom. Lactation alone typically triples food
No postpartum estrus in hamsters.