Adaptable birds catch caterpillars, as described in Science, vol 310, p304 and ScienceNOW 14 Oct 2005.

Great tits are small European birds that breed each Spring and feed on caterpillars. As they need the most food when they are raising their young, it is useful for the birds they lay their eggs in time to hatch when caterpillars are most abundant. The time of caterpillar abundance varies each year depending how early the warm spring weather starts, so it is also useful if the birds are able to vary their breeding time. Ecologist Marcel Visser of the Netherlands Institute of Ecology and colleagues have studied data on breeding habits of great tits living in a Netherlands national park from the past 32 years to see if the birds could vary their breeding habits with variations in climate.

Most of the birds did not change their breeding habits, but some birds appeared to be tuned in to climate variation and laid their eggs earlier in warm Springs and later in cool Springs. These adaptable birds had more surviving offspring than the less flexible birds. Most interesting is that the ability to adapt appears to be passed on to the next generation, i.e. it is genetically programmed. The researchers say there is not enough long term data to be sure that the birds are evolving greater flexibility but they think that the more adaptable birds will come to dominate the population.

Editorial Comment:  This study cannot prove that birds are evolving flexibility. It proves that some birds are able to change their breeding cycle with seasonal variations and some aren’t. The fact that more of the flexible birds are surviving is not evolution because they already had the ability to do this and when the climate changed they had an advantage over the less flexible birds. This is natural selection, but it is not evolution.

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