Thrush survive in just three remnants of the Taita Hills forest in southeastern Kenya - the highly degraded Chawai, the moderately degraded Ngangao and the virtually undegraded Mbololo forest fragment.
The mathematical concept of symmetry has many applications, such as in chemistry and biology. Symmetry has been thought for some time to be an important indicator of good health and survival prospects - even for humans. People with more symmetric faces are more generally found attractive, and so have a better chance of success in reproduction and genetic survival. Also, severe asymmetry can indicate genetic problems, or that the individual suffered from infections that affected its development - suggesting to potential mates that they should look elsewhere.
Similarly, it appears that levels of symmetry for a whole population can predict the survival prospects for the group. In order for fluctuating asymmetry (FA) to be a useful indicator of population decline, it is vital that it becomes apparent in populations before irreversible damage is done. The research, reported in the journal Conservation Biology, gives the first unambiguous evidence that this is the case. Using sophisticated mathematical modelling of the populations and statistical techniques to remove error and experimental bias, the researchers discovered that levels of asymmetry became higher the more degraded the forest fragment was. Compared to the population in the undisturbed Mbololo fragment, the asymmetry was 2.5 times higher for the population in the moderately disturbed Ngangao and 8 times higher in the highly disturbed Chawai. Meanwhile, the survival rates were only affected for the Taita Thrush population in Chawai, suggesting that asymmetry does appear before significant damage is done to the population.
Using asymmetry as an early danger sign will have a real impact for conservation programs ever