AASAGACITY.NET
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A scoring system to define a species; an evaluation of a taxon/some taxa, using the Sensible Species Definition.  5 points between taxa makes a different species.



Geographic separation/Chance
of cross-breeding
Physical differences Voice

Song/Calls

Habitat preference
Behaviour
including
migration
Known
genetic differences

Assuming a rate of divergence in mtDNA of 1.6–2.0% per million years. (Fleischer et al.1998; also see Lovette 2004; Ho 2007; Weir and Schluter 2008).

From mtDNA analysis, species take from between 0.2 to 5.5m yrs.  ("The Speciation & Biogeography of Birds", Ian Newton, 2003.

MU

Total points
sp
or
subsp

Scoring 0-1-2-3 0-1-2-3 0-1-2-3 0-1-2-3-4 0-1-2-3 0-1-2-3-4-5

A SENSIBLE SPECIES DEFINITION (Anderson 1998 and 2012)
Species are populations that are interbreeding and which are reproductively isolated from other such populations by their reproductive isolating mechanisms.
These may include -
     geographic separation / chance of cross-breeding;
    morphological and plumage differences;
    voice;
    habitat preference;
    behavioural differences such as nest-building, social grouping or migration;
    consistent mtDNA and other genetic differences.
Each mechanisms can be weighted according to the strength of difference from a recognised species and given a score between 0 and 5; a total of 5 would give the taxon species status.
0
 
 
 
 
 
1
 
 
 
 
 

2

 
 
  
 
3





4





5




Broad hybrid zone





e.g. Narrow and stable hybrid zone,
or good chance of interbreeding.



e.g A small chance of interbreeding.



No chance of interbreeding, or successful breeding is not known to occur where there is breeding overlap.


Physical characteristics a little different



Physical characteristics noticeably different.



Physical characteristics very different.


Physical characteristics completely different.
Not so different voice range and/or song phrases.




Noticeably different voice range and/or song phrases,






Completely different voice range and/or song phrases.
Similar or slightly different habitat preferences.



Noticeably different habitats.







Completely different habitats.
Slightly different behaviour.






Noticeably different behaviour.






Very different behaviour.
Genetic differences are barely measurable.


Genetic
differences are definitely measurable.



Genetic differences indicate larger divergences.

Genetic differences are large enough to probably have non-viable offspring.


Genetic
differences are so great that viable inter-breeding would be impossible.




North American regular hybrids
Comparison of a universally accepted species with another taxon or taxa, e.g. a subspecies
 Geographic separation/Chance
of cross-breeding

Physical differences
Voice

Song/Calls

Habitat preference

Behaviour
differences
Known
genetic differences

Total Points
sp
or
subsp
Research -
Passerina cyanea
Indigo Bunting
Passerina c. amoena Lazuli Bunting
Conclusions -
These birds evolved as one species which was separated by recent glacial cycles. Evolved differences during those millenia have resulted in two subspecies which have since come together and have an extensive hybrid zone in the mid-west USA. (The Speciation & Biogeography of Birds", Table 10.3, Ian Newton, 2003). 
The separation has not been long enough to result in two species.

Research -

There are other North American sub-species pairs which evolved together, then separated for many millenia, then came together again; the pairs that migrate to the same places but return to their own breeding grounds have been given a behaviour difference score of 1.
Colaptes auratus Northern Flicker,
yellow-shafted 
Colaptes auratus cafer Northern Flicker, red-shafted 

Icterus galbula Baltimore Oriole
Icterus galbula bullockii Baltimore (Bullock's) Oriole

Pipilo erythrophthalmus EasternTowhee
Pipilo e. maculatus Spotted Towhee

Dendroica coronata Yellow-rumped (Myrtle) Warbler
Dendroica c. auduboni Yellow-rumped (Audubon's) Warbler

Pheucticus ludovicianus Rose-breasted Grosbeak
Pheucticus l. mealanocephalus Black-headed Grosbeak
Conclusions -
This last one is a surprise (to me anyway) and maybe there is some genetic work done that could boost the score. 
In the meantime perhaps the two together should be called Black-headed Grosbeak.

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