Macroevolution concerns the development of biological patterns among species and higher taxonomic groupings such as genera, families and orders, and so is the branch of evolutionary biology relevant to the question of why some kinds of birds are more migratory than others. The pattern of correlation between migratory behaviour and feeding location among birds is particularly strong at family level, and may have arisen through coevolution of foraging and ranging behaviour.
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Species that exploit resources occurring in exposed locations may need to migrate to track seasonal abundances. 'Exposed' resources are variable in time and space, both because they are easily located and consumed by foraging animals, and because they are subject to environmental factors; they can be blown away by wind, washed away by rain, dried up in the sun.
Consequently, exposed resource foragers may also need to adopt 'coarse-scale' searching tactics involving rapid, superficial searching of a wide area to locate temporarily abundant resources, and be behaviourally flexible to enable a food source to be exploited, no matter where it happens to occur. Such 'opportunistic' foraging facilitates migration, since it enables rapid location of food in unfamiliar environments.
Species that exploit 'buffered' resources can stay put, as their food supply is less subject to wind, rain, sun or frost, and less susceptible to over-exploitation by consumers. Buffered resource foragers can therefore adopt a 'fine-scale' searching mode, involving detailed combing of substrates, and can also rely on stereotyped foraging actions to exploit a food supply that is reliably available.
Such 'methodical' foraging is most effective where an individual has an initmate knowledge of a home range, and will be less effective in the unfamiliar environments encountered on migration, which therefore increases the advantage of remaining resident. |
