Question 3: Discuss Excellence

Practises Social behaviour & spatial behaviour

Australian chestnut-crowned babblers (Pomatostomus ruficeps) live in social groups of up to about 25, dust-bathing, preening and feeding together. They search for food as a group: insects, spiders, small amphibians, crustaceans and reptiles, and fruit and seeds. At night they crowd into one large central nest; when alarmed they huddle under thick foliage or fly up into the lower canopy, chattering loudly. Breeding runs from about July to November, with one large clutch from all the breeding pairs. The whole group builds the single nest, feeds the incubating females and defends the breeding territory, and a pair seldom tries to breed without help. There are often about 4 breeding males and as many as 12 helper-males that do not breed. Kin selection seems to matter: females will not help care for young they are not related to.

Examine how social behaviour can lead to successful reproduction in the chestnut-crowned babbler.

The 2024 paper, page 10 ↗ Marking schedule, page 6 ↗

Work it out

Try it on paper first. Stuck? Take one hint at a time.

1 Start from the explain answer: how does the defended territory reach the chicks?
With the area marked and defended, the young are raised with more food and less disturbance, so more of them live to breeding age.
2 What does group living do for the breeders themselves?
They have potential mates close at hand, so less energy goes into finding one, and more is left for raising young.
3 How do foraging together and preening reach reproductive success?
Foraging together saves each bird energy, and preening removes parasites and strengthens bonds. Both keep adults alive and in condition to breed, which increases reproductive success.
4 What part does kin selection play?
Only relatives, the helper-males, take on the costly work of rearing chicks. The chicks carry their alleles, so each extra chick that survives passes those alleles on, even though the helpers fathered none of them. The unrelated females share no alleles with the chicks, so for them the cost would bring no return.
5 Why does kin selection keep going in the population?
With many related helpers, the chicks get far more care than one pair could give, so more survive. Those chicks carry the shared alleles, including any that favour helping, so the helping behaviour itself is passed on.

Answer Defending a territory means the young are raised with more food and less disturbance, so more reach breeding age. Living in a group gives the breeders mates close at hand, saving energy for raising young. Foraging together saves each bird energy, and preening removes parasites and strengthens bonds, so adults stay alive and in condition to breed: all of these increase reproductive success. Kin selection explains who helps. Only relatives, the helper-males, take on the costly work of rearing chicks; the chicks carry their alleles, so each extra survivor passes those alleles on although the helpers fathered none of them. The unrelated females share no alleles with the chicks, so helping would cost them for no return. With many related helpers, the chicks get far more care than one pair could give, more survive, and the shared alleles, including those behind helping, continue in the population. That is how social behaviour leads to successful reproduction.

What the marker wanted

Achieved The describe points: territory and its advantage, kin selection, two advantages of social behaviour, and why the helper-males help and the unrelated females do not.
Merit Those explained: the territory’s resources, kin selection as altruism among relatives, two ways social behaviour raises survival, the helper-males’ alleles, and the females’ reason.
Excellence Discusses two things. How cooperation leads to reproductive success: young raised with more resources in a defended area, so more reach breeding age; mates close at hand; foraging together saving energy; preening removing parasites and building bonds. And the role of kin selection: only related helper-males rear chicks, passing on their own alleles without fathering any, AND the unrelated females do not help because they share no alleles; and kin selection giving the chicks more care, so the shared alleles and the helping behaviour continue. Each point ends on survival or reproductive success. Two give E7; three or more, E8.

One answer, N0 to E8. In 2024 the Excellence points are counted higher than usual: two give E7, three or more E8.

In our words, from NZQA’s 2024 marking schedule.

Common mistake

Explaining each behaviour well but never tying it to how many babbler chicks survive to breed. NZQA’s 2024 report says many answers failed to make that final link.

How did it go?

Got it moves it further out. Review brings it back tomorrow.