Question 2: Discuss Excellence

Practises Navigation over long distances

The indigo bunting (Passerina cyanea) makes a long journey every year, and migrates only at night. It flies roughly 2000 km each way between its breeding grounds in eastern North America and its wintering grounds, which stretch from southern Florida to southern Central America; the paper shows both on a map.

Discuss how, despite the difficulties of a long journey, the yearly migration has enabled the indigo bunting population to be maintained.

The 2022 paper, page 5 ↗ Marking schedule, page 3 ↗

Work it out

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

1 Start from the explain answer: what are the costs of the journey?
Buntings can lose their way or be blown off course, and run out of energy; they can be eaten by predators on the way; they can starve with no food en route; and the flight uses so much energy that a bird may arrive too depleted to court and breed.
2 What does wintering in the south gain?
Warm temperatures, so less energy goes on keeping warm, and a steady food supply, so birds can grow, store energy for the return, and survive the winter.
3 What does breeding in the north gain?
Good breeding conditions, so more offspring survive. Moving away also leaves behind predators and parasites that depend on them, and birds from different places meeting on shared breeding grounds mix their genes.
4 Weigh the two sides.
Each cost can kill or stop a bird breeding, but each benefit raises survival or breeding for the many that complete the trip. Because more birds survive the year and rear more young than if they stayed, the benefits outweigh the costs.
5 So what does that mean for the population?
Survival and reproductive success are higher with migration than without, so the repeated journey has kept the indigo bunting population going.

Answer The journey has real costs: buntings can lose their way or be blown off course, and run out of energy, be eaten by predators, starve for lack of food en route, or arrive so depleted that they cannot court and breed. Against these, wintering in the south gives warm temperatures, so less energy goes on keeping warm, and a steady food supply, so birds survive the winter and store energy for the return. Breeding in the north gives good conditions in which more offspring survive, leaves behind predators and parasites that depend on them, and lets birds from different places mix their genes on shared breeding grounds. Each cost can kill a bird or stop it breeding, but each benefit raises survival or breeding for the many that complete the trip, so the benefits outweigh the costs. Survival and reproductive success are higher with migration than without, which is why the repeated journey has kept the population going.

What the marker wanted

Achieved The describe points: migration, circannual rhythm, the cue, a night navigation method, a benefit.
Merit Those explained: all-year good conditions, night navigation by internal and external cues, several methods, the celestial pole or magnetic field, reproductive success, and a difficulty.
Excellence A full discussion of what migration costs the bunting and what it gains. Benefits include warm temperatures (less energy spent keeping warm), a constant food supply (growth and reserves for the return), better breeding conditions (more surviving offspring), escape from predators, parasites and disease, and genetic mixing. Costs include getting lost or blown off course, predation on the way, starvation, and arriving too depleted to breed. The benefits must outweigh the costs, so survival and reproductive success increase. E7: one cost and one benefit, linked to overall survival. E8: two costs and two benefits, linked the same way.

One answer, N0 to E8. In 2022 Question Two, Excellence is counted in costs and benefits: one of each, linked to survival, gives E7; two of each gives E8.

In our words, from NZQA’s 2022 marking schedule.

Common mistake

Ending on “the benefits outweigh the costs” without a specific cost to weigh, or listing costs and benefits without linking them to survival and reproductive success. NZQA’s 2022 report names both.

How did it go?

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