60 Social Hierarchy in Pukekos

Key Idea: Hierarchies in social birds can be determined by identifying the winners and losers in conflict situations. The pukeko is a relatively common New Zealand bird, typically found in swamps and marshes. In contrast to most other bird species which form mating pairs, pukeko cooperate as a group or 'commune' with coordinated activities. More than two birds will defend territory, court and copulate, lay in, incubate and defend a single nest, and feed and care for chicks. Most social animals establish a strict ranking order or hierarchy (sometimes called a pecking order) to reduce fighting between group members.

During activities such as feeding, some pukeko in close contact situations may avoid contact by taking food a short distance away from the others before eating. Other members of the group (the winners), chase away losers that come too close. In any encounter between two birds there is a winner and a loser. To determine if there is a social hierarchy, it is necessary to identify each bird individually and list them on two axes in the same order (see table below). One axis is then labelled the winner and the other, the loser. Results showed that males dominate females, and older birds dominate younger birds. The social organisation of a stable group is dependent on the fact that these birds act at all times in accordance with their status. Chicks are initiated into the hierarchy at a very early age.

This material has been reproduced with kind permission of Dr. John Craig, University of Auckland. It has been modified from part of the Senior Biology Resource Unit: The Pukeko.

1. Circle the square on the chart (on the right) in which this context appears: pukeko W6 defeats pukeko B6.

2. Complete the summary in the table below for the four birds:

Pukeko No. won No. lost Total % Won

W6

L9

L8

W7

3D

A pukeko showing its white tail feathers used as a 'flag' in signalling alarm, aggression, and submission.

Loser Outcomes of 246 meetings between individual pukeko in a population of seven birds Winner W6 2F L9 W3 L8 B6 W7

W6

2F 13

L9 29 23 2 3

W3 19 12 9 1

L8 15 9 13 7

B6 18 3 5 6 11 6

W7 12 1 4 3 13 9

3. How does the organisation of the table (above right) reflect the social rank of each pukeko?

4. What is different about the results for L9, W3, and B6?

5. Explain what these unexpected results mean in terms of what happens when for example, B6 meets W7:

6. W6, 2F, and L9 are adult males and W3, L8, and B6 are adult females. Explain the relationship between sex and status in this group of pukekos:

A complete stranger, a male pukeko called R1, was adopted by the group for territorial defence. The table below shows the result of encounters between the new bird and others in the group immediately after the adoption. Each encounter is represented by a dot in the appropriate square.

8. Between which two birds does R1 probably rank?

9. Predict the probable result of an encounter between R1 and W3:

10. What factors might be important in the maintenance of a stable hierarchy within the group?

11. (a) Describe the effect of social status on the outcome of interactions between members in a hierarchy:

(b) Describe the benefits to social animals of having a hierarchy to control social interaction:

Loser W6

2F

L9

W3

L8

B6

W7

R1 The outcomes of encounters between a new bird (R1) and the rest of the group

Winner W6 2F L9 W3 L8 B6 W7 R1