Q19 - Foraging Energetics and Territory Defence

Theoretical 1 Real exam question - full text reproduced under IBO's CC BY-NC-SA 4.0 license

Foraging & Anti-Predator Behavior Aggression, Territoriality & Social Structure

Defending a territory requires time and energy. Any animal should only defend territories if the benefits of defence outweigh the costs.

Consider a bird species that feeds only on the nectar of flowers. The table below shows the foraging time required for the bird to meet its daily energy requirements when it obtains given amounts of nectar per flower.

The metabolic costs associated with various activities of the bird are as follows:

Activity	Cost
Foraging for nectar	500 calories/h
Sitting on a perch	200 calories/h
Territory defence	1500 calories/h

Nectar per flower (microlitres)	1	2	3
Time to get energy (hours)	8	4	2.7

If a bird defends a territory, it excludes other nectar consumers and this increases the amount of nectar per flower from 2 microlitres to 3 microlitres. The bird thus spends less time foraging and more time sitting on a perch.

Q19.1. Calculate the energy saved by this bird, with reduced foraging time, as compared to an individual which is not territorial. Give your answer in calories.

Q19.2. If the bird needs to spend 0.28 hours per day defending territory, instead of perching, what is the cost of defence faced by the bird, compared to a bird which is not territorial? Give your answer in calories.

Q19.3.1. Under the conditions specified above, the bird is likely to show territorial defence.

Q19.3.2. The birds will almost never be territorial if it reduces the amount of time spent perching.

Q19.3.3. The birds will almost always be territorial if the cost of foraging per hour is higher than the cost of defence per hour.

Q19.3.4. The birds will not show territorial defence when the net costs, incurred by defence, are lower than those of not defending a territory.

← Previous: Q18 Next: Q20 →

Question reproduced from IBO 2023, Theoretical Paper 1, licensed under CC BY-NC-SA 4.0 - attributed to the International Biology Olympiad. Open the full exam PDF