Blackcap Warblers were experimented on to assess their recent changes to migratory behaviour. The clutch, as it grows in the nest, can see the sky at night time and the celestial patterns of the stars become imprinted in the juvenile brains (see 'celestial imprinting' page).Northern European populations of blackcap warblers migrate at nighttime and utilize the celestial patterns to navigate to the desired location. There is a population from the Cape Verde Islands (off West Coast of Africa) and this population does not migrate anymore. In the experiment (Berthold et al., 1990) birds from both populations were crossbred and the results showed that there was a reduction in the urge to migrate (zugunruhe) as well as a change to migratory orientation behaviour, highlighting that both these behaviours have a heavily genetic basis.
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| Figure 1. Showing an Emlen funnel and the scratch marks a bird makes when it begins to exhibit 'migratory restlessness' (zugunruhe). The scratch marks will predominantly be in the approximate direction that the bird wishes to migrate. Depending on the parental genetics passed down, the direction of scratches may differ or reach a median if a hybrid. |
References:
Berthold, P., Wiltschko, W., Miltenberger, H. & Querner, U. (1990). Genetic transmission of migratory behaviour into a nonmigratory bird population. Experientia. 46(1): 107-108.
Figure 1. https://www.rspb.org.uk/birds-and-wildlife/bird-and-wildlife-guides/bird-a-z/b/blackcap/
Figure 2. http://www.mhhe.com/biosci/genbio/maderbiology7/student/olc/chap22-outline.mhtml