Statistical Problems in the Study of Seed-Eating Birds

Summary

The ‘profitability’ of different sizes of seeds can be assessed as: kernel weight divided by the time taken to eat (handling time). Experiments with bullfinches eating sunflower seeds showed that handling times for larger seeds may be greater or smaller, depending on experimental context, and on which dimension of seed size is measured. There was very little variability of kernel weight among seeds of a given size, but handling times were highly variable, and bullfinches apparently judged the ease of handling by brief manipulation of seeds before choosing one to eat. Many periods of handling ended without the seed being eaten, owing to deliberate or accidental dropping, and cause difficulties in calculating average handling times that reflect birds’ likely feeding costs. Field observations of bullfinches feeding on ash seeds implied that wild birds may forage similarly to those in laboratory experiments.