Tuesday, 1 April 2014

Another Armchair Tick?

As we all know, Corn Buntings, across their European range, show a clear pattern of microgeographic song variation.  However, the findings of a new paper just published (Riza & Ember, 2014) are still somewhat surprising.

Corn Bunting is widely distributed across most of central Europe and it has long been recognised as variable with as many as six subspecies being proposed based not only on variation in its extremely complex song but also on very subtle variations in barring, colouration and morphometrics.  Extensive work has already been done on variations in its song and it seems that the ‘jangling keys’ description that we see repeated in so many field guides is an over-simplification brought about by the limited range of human hearing.  The reality is that there may be as many as six different bunches of keys!  These have now been distinguished in this latest study by measuring time and frequency characteristics with both univariate and multivariate analyses.  The results demonstrated significant differences in song characteristics among regions, and discriminant function analysis classified 80% of songs to the correct region. Divergence of song can occur rapidly and be of prime importance in causing reproductive isolation and speciation.

The authors propose that two species groups be recognised.  The northern group comprising two subspecies they name Wheat Bunting (Miliaria durumi), while the southern group made up of four subspecies retains the existing name Miliaria calandra but is re-named Barley Bunting, recalling the old Celtic name ‘fat bird of the barley’.

Riza and Ember, in their work examining contact zones between northern and southern divergent groups of birds travelled to the foothills of the Alps in Italy and began looking for locations where the northern and southern groups of Corn Buntings came into contact. In Piedmont, they discovered locations where the northern and southern forms co-existed, and began their work using sound, morphometrics, and genetic analysis to answer the vexing question of whether there was indeed more than one species.  Their aim was to discover whether there was a gradual change in traits (genetic, morphological, song, etc) as one would expect if there was gene flow between the two forms or whether the two forms overlap while maintaining their distinctive differences, indicating that they maintain reproductive isolation from one another.

'Jangling keys'

As well as their work on vocalisations, Riza and Ember also set out to examine functional relationships between the morphology of buntings and their behaviour. They found that Wheat Buntings have relatively longer feet than Barley Buntings, and they also have relatively long back claws and toes. This they thought may be related to the circumference of the birds’ favoured perches with power cables being more frequently used in the north while barbed wire is the more commonly used in the south.  Although the differences in size were statistically significant, they were not thought to be on a scale that would affect either species’ ability to sit on a fence post for long periods.  It was noted that song flights with dangling legs were common to both species in spite of the size differences noted in their feet but that the song flights of Barley Buntings were of longer duration, probably because they have wings of higher aspect ratio than Wheat Buntings, and they also have a lower wing loading.

Their conclusions are now published and once again we find ourselves totally amazed by a split of a species we thought we knew well.  We recommend that you try to read the paper in full for yourself.

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