Testing a hypothesis—experiments to test hypotheses on the migratory behaviour of blackcaps have been carried out.
In the 1950s, blackcap warblers (Sylvia atricapilla), a small European songbird, began to be observed wintering in Great Britain, instead of North Africa. These observations led to the formation of hypotheses regarding blackcap migratory behaviour: were the changes due to inherited (innate) factors, was it a response to the environment or did the birds simply lose the ability to migrate normally?
To test these hypotheses, it was necessary to use experimental methods, as fieldwork would have been unfeasible. The birds were kept in specially designed cages that could register if birds began to become restless during the migratory season and then what direction they tried to orient towards.
The results showed that the offspring of birds that migrated to Britain oriented consistently in a NW direction, despite being raised in isolation from their parents. Follow-up genetic analysis showed a strong heritability for this trait in both British wintering blackcaps and those from other parts of Europe. The authors were led to suggest that:
“Under moderate selection intensities and environmental conditions similar to those presented in this study, the southern German blackcap population could evolve into a short-distance migrant in 10-20 generations.” (Berthold and Pulido; p311)
These results represent rapid evolutionary changes in behaviour- it is worth considering what selection pressures are working to promote these changes. Can you relate this back to the Evolution/Natural Selection topics (5.1/5.2)?
Berthold, P and Pulido, F. Heritability of Migratory Activity in a Natural Bird Population.
Proc. R. Soc. Lond. B. 257. 1994. 311-315. Web. Mar 15, 2016. Full text available: at https://www.researchgate.net/profile/Francisco_Pulido/publication/216768532_Heritability_of_migratory_activity_in_a_natural_bird_population/links/0fcfd50c5c5adc29c9000000.pdf
Berthold, P. et al. Rapid microevolution of migratory behaviour in a wild bird species. Nature. 360. 1992. Web. Mar 15, 2016.
“Identify A Blackcap, Sylvia Atricapilla”. Birdfieldguide.co.uk. N. p., 2016. Web. 15 Mar. 2016.