Question 3: Explain Merit

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.

Explain how the territory and the group’s social behaviour help the babblers survive and breed, why the many helper-males support the population, and why the unrelated females do not help raise the young.

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 The describe answer said the territory gives the group resources. Why does that matter?
Defending it keeps rival babblers off its food and nest sites, so the group has more of both, which raises every member’s chance of surviving and breeding.
2 Why does finding food together raise survival?
Their food, insects, spiders, small reptiles and fruit, is scattered. Many birds find it sooner, and some can watch for predators while others feed, so each spends more time feeding and gets more energy.
3 Why does preening raise survival?
Parasites take blood and spread disease. Removing them keeps the birds healthier, and the bonds preening builds keep the group together without fighting.
4 What does kin selection mean for a bird that helps?
Animals that share alleles behave altruistically towards each other because helping relatives survive raises the chance that those shared alleles are passed on, through the young.
5 So what do the helper-males contribute?
They are relatives of the breeders, uncles or older brothers of the chicks. By building the nest, feeding the incubating females and defending the territory, they help the chicks survive, and so get copies of their own alleles into the next generation without fathering any chicks.
6 Why do the unrelated females not help?
They share no alleles with the breeding females’ chicks, so helping would cost them energy and risk while passing on none of their own alleles. The sacrifice gains them nothing.

Answer Defending a territory keeps rivals off the group’s food and nest sites, raising its members’ chances of surviving and breeding. Finding food together means scattered food is found sooner and some birds keep watch while others feed, so each gains more energy. Preening removes parasites that spread disease and builds bonds that keep the group together. Kin selection means animals sharing alleles act altruistically towards each other, because helping relatives raises the chance those alleles are passed on. The helper-males are relatives of the breeders, so by building the nest, feeding the incubating females and defending the territory they help the chicks survive and pass on copies of their own alleles without fathering any. Unrelated females share no alleles with the chicks, so helping would cost them without passing on any of theirs, and they do not.

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 Explains: a defended territory giving more resources and so better survival and reproduction; kin selection as altruism between animals that share alleles, raising the chance those alleles are passed on; one way social behaviour raises survival, such as foraging together; a second, such as preening against parasites and disease; the helper-males passing on their own alleles through chicks they did not father; and the unrelated females not helping because they share no alleles, so the sacrifice is not worth it. Three make M6.

One answer, N0 to E8. Merit points sit above the Achieved ones: two give M5, three M6.

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

Common mistake

Explaining the territory and the cooperation well but not kin selection and why it matters. NZQA’s 2024 report says this was common in Merit answers to Question Three.

How did it go?

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