Question

1. A group of researchers is collecting data on the foraging patterns of a population of wagtail birds, which feed on an insect called the dung fly. These graphs show some of the data collected by the team:

16 14 12 10 5 8 9 10 Dung fly body length (mm) Figure A: The relationship between the calories gained by the wagtail and the size of its prey (the dung fly)

Given the data presented in each of the graphs, what conclusion can you draw from this data about the feeding practices of the wagtail birds?

2. Describe a specific example of a visual communication used by animals in response to an external stimulus. Explain how this type of communication can result in a change in behavior.

Answer 1

Answer 1.

From the data given, it can be seen that more calories are obtained from the averagely sized wagtail. If the size of the dung fly is small, few calories are obtained by the wagtail. If the size of the dung fly is large, then also few calories are consumed.

The second graph shows the percentage of dung flies that were eaten out of the total that was present. The most eaten were those which had an average body length of 7mm. Out of the available flies, almost 50% of them were eaten by the wagtails. The other sized flies were also eaten, but not as much as those with the average length.

From this, we can conclude that the wagtails feed on dung flies which have an average size. This helps to minimize the foraging costs and obtain the maximum calories. The smallest and the largest sizes are available in far fewer numbers. The calories spent on finding the biggest dung flies are much more than that consumed as the large size makes it difficult to consume it all at once and the leftover soon rots away. The small sizes are insufficient in calories and must be more in number to satisfy the energy needs.