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IBIS  |  Volume 159  |  Issue 2  |  April 2017

 

The April issue of IBIS contains 16 Original Articles and four Short Communications.

Here are four of the many highlights in this issue. 

The point of a Guillemot’s egg  

Tim R. Birkhead, Jamie E. Thompson, Duncan Jackson &
John D. Biggins
 
One of the first ‘facts’ we learn as budding ornithologists is that the uniquely pyriform (pear-shaped) egg of the Common Guillemot Uria aalge is an adaptation to prevent the egg from rolling off the narrow cliff ledge on which it is laid. A complete lack of supporting evidence has not prevented this from entering the canon of ornithology. New research by Tim Birkhead and colleagues at the University of Sheffield casts doubt on this widely held view, and instead proposes that the shape of a Guillemot’s egg is an adaptation to prevent it from becoming crushed by the mass of birds nesting on crowded ledges and to prevent it from accumulating a contaminating layer of soil and faecal debris. The shape of the egg means that more of it is in contact with the substrate, thus distributing the weight of any impacts over a larger area, and the accumulation of debris on the eggshell is significantly lower at the blunt end of the egg, which is more porous and from which the chick eventually emerges. The paper therefore relegates the ‘rolling off a cliff’ theory to that of an urban, or perhaps a marine, myth, and is cautionary illustration of the need to question even the longest-held theories.


Environmental factors determining the establishment of the African Long-legged Buzzard Buteo rufinus cirtensis in Western Europe 
Darío Chamorro, Jesús Olivero, Raimundo Real & Antonio-Román Muñoz
Climate warming is likely to bring new bird species to Europe as their current range limits in North Africa shift northwards. In recent years, the African race of the Long-legged Buzzard Buteo rufinus has appeared with increasing regularity in the Iberian Peninsula, having crossed via the Strait of Gibraltar, prompting suggestions that the species may colonise southern Europe. Darío Chamorro of the University of Malaga and colleagues use a range of spatial modelling methods to assess the likely suitability of the newly occupied areas, and conclude that there are sufficient areas of suitable habitats in Iberia to allow the species to permanently colonise Iberia and to establish a population that may spread to other parts of Europe. Their methods present a way in which the likelihood of colonisation of southern Europe by other African species could be assessed. 

 

A novel method for quantifying overdispersion in count data and its application to farmland birds 
Barry J. McMahon, Gordon Purvis, Helen Sheridan, Gavin M. Siriwardena & Andrew C. Parnell 
A common problem in analysing bird count data is that of overdispersion compared with a standard Poisson distribution, whereby the variance is greater than the mean. This is usually treated as a nuisance factor to be controlled and then ignored, but as Barry McMahon of University College Dublin and colleagues point out, overdispersion may actually reflect biologically interesting processes, such as flocking. Using data on birds on Irish farmland, the authors present a novel method for modelling overdispersion as a biologically interesting phenomenon. They find that overdispersion was higher on dairy than on non-dairy farms, suggesting that there is a systematic difference between the two systems in the extent to which bird counts are distributed. The authors make available all their code and data to enable others to use and develop this methodological novelty.

 

Phylogeography of the Common Pheasant Phasianus colchicus
Nasrin Kayvanfar, Mansour Aliabadian, Xiaoju Niu, Zhengwang Zhang & Yang Liu
The Common Pheasant Phasianus colchicusis the world’s most widespread pheasant species and occurs in a wide range of distinctive forms of the males’ colourful plumage, with the large number of subspecies being divided into five main subspecies groups. Using two mitochondrial and two nuclear loci, Nasrin Kayvanfar of the Ferdowsi University of Mashhad in Iran assess the relationship between these groups and attempt to reconstruct the phylogeography of the species. They find that the basal form is the subspecies elegans of Yunnan, confirming previous suggestions that the species evolved originally in south-eastern China. Initial divergence in Pheasant population is dated to around 3.4 mya, and the species’ initial dispersal into the Western Palaearctic, which may have followed one of two routes, to around 2.5-1.8 mya. The authors conclude that there is little correlation between the morphological differences between the many subspecies and their genetic differences.

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Images credits (from top)
Guillemot's egg | Didier Descouens | Wikimedia Commons

Black-tailed Godwit | Andreas Trepte | Wikimedia Commons
Long-legged Buzzard | @stevedudley_
Yellowhammer | @stevedudley_
Common Pheasant | Ken Timothy | Wikimedia Commons
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Black-tailed Godwit image © Andreas Trepte | via Wikimedia Commons | CC BY-SA 2.5