Adoption in the emperor penguin

Issue 9, June 1997

Emperor penguins (Aptenodytes fosteri) breed in the Antarctic, under the harshest conditions for any species of bird. The ground surface is solid ice, the mean air temperature is - 20° C and the mean wind speed is 25 km per hour. Each year, the female lays one egg, which is then incubated by the male. He holds the egg on his feet, and thus off the ice, for sixty days. When the egg finally hatches in late winter both parents feed the chick. Emperor penguin chicks beg food from any adult but parent birds only feed their own chick, see Figure 1. By the end of the summer the chick is independent. Some of the key events in the breeding season of the emperor penguin are illustrated in Figure 2.

Figure 1. Emperor penguin chick being fed.

Figure 2. Summary of the key events in the breeding season of the emperor penguin. The presence and absence at the colony of breeding birds and the period of adoption are indicated.

Three researchers* carried out a study of the emperor penguin in 1989 and 1993. The researchers were particularly interested in the adoption of emperor penguins chicks by other adult penguins. [The scientists defined adoption as "the brooding, defending and feeding of a chick by an adult other than the parent".] These are usually birds that have failed to breed during the season, being non-breeding unmated birds (usually females) or non-breeding pairs.

The researchers found that adopted chicks were either 'kidnapped' by adults other than their genetic parents or were found wandering around the colony by other adult birds and then adopted. When kidnapping takes place the researchers observed that the biological parent always fought the intruders (either by pecking at it or striking it with a flipper) but that if the kidnapping was successful the parent almost never tried to re-capture its chick. Chicks wander in search of food, though there is the danger that if they are isolated from adult birds they may be attacked by giant petrels, large sea birds.

Adoptions usually occur when the chick is able to regulate its own body temperature; at this time the chicks often huddle together in a creche. The scientists also found that most adoptions are only temporary, however. For example, in 1993 the mean length of time that adoption lasted was 1.89 days.

* Jouventin, J., Barbraud, C. and Rubin, M. (1995). Adoption in the emperor penguin, Aptenodytes fosteri. Animal Behaviour, 50, 1023 - 1029.

Intermediate tier

1. How many months do the adult birds spend in the Antarctic from the time of their arrival to the time of their departure? (1)
2. What is the length of the incubation period? (1)
3. Approximately how old are the chicks when they depart? (1)
4. Why do you think females spend so long at sea after laying the egg? (1)
5. Why do penguins not build a nest to hold the egg? (2)
6. Suggest, and explain, one advantage to the penguin chicks of getting together in a creche. (2)
7. Suggest one advantage to emperor penguins of raising their chicks in the Antarctic winter? (2)
8. Outline one advantage to a penguin chick of being adopted by an adult that is not its biological parent. (2)

We are grateful to Academic Press for permission to reproduce Figure 2 from the article by Jouventin et al in Animal Behaviour (1995).

Higher tier

1. What is the length of the incubation period?(1)
2. Approximately what percentage of a mature male penguin's time is spent fishing at sea during the year? (1)
3. Why do you think females spend so long at sea after laying the egg?(1)
4. The researchers recorded 351 cases of adoption out of 2068 chicks in the colony. What percentage of the chicks in the colony were adopted? (1)
5. Why do penguins not build a nest to hold the egg? (1)
6. Why are the birds limited to only laying one egg? (1)
7. Suggest, and explain, one advantage to the penguin chicks of getting together in a creche. (2)
8. Why does a parent emperor penguin put up a struggle to resist the kidnapping of its chick by an intruder? (2)
9. Why do giant petrels only attack isolated penguin chicks? (2)