Ramhling Notes on Birds. 105 



species when mixed with specimens of a closely-allied resident 

 species^ if we know the governing percentage of difference 

 between the lengths of the first and second primaries, of 

 which the following may l)e taken as examples : — 



Per cent. 



{Fiscus coUaiis, Resident 58 

 Lanius minor, M.\gva.nt 2S 



(A Iseonax adusta. Resident 45 

 Muscicapa grisola, Migrant 27 



J Ileterocorys hreviungius, Resident 46 



\_Pinarocorijs nigricans, Migrant 27 



rBradijpterus hrachypterus, Resident 62 



' Lusciniola gracilirostris, Resident 50 



I Acrocephalus bceticatiis, African migrant 2G 



^ „ arundinaceus, European migrant 17 



Where comparisons are made between more active species 

 and those of less active habits, we find it proportionately 

 r(?flected in the first primary. In some birds the first 

 primary has entirely disappeared as a result of the great use 

 to which the wings are put. Even in such cases we can 

 judge, though with less certainty, by the comparative length, 

 breadth, and stiffness of the first primary-covert. Whether 

 what appears to be the first primary-covert is really the first 

 primary in a new position I cannot say, not having examined 

 young birds to find out ; but in any case, when speaking of 

 the outermost primary in such cases we should call it- the 

 second and not the first primary. However, to return to the 

 Grass-Warblers, an application of this principal of measure- 

 ments for diagnosing the different species greatly simplifies 

 the difficulty, for, if we take, say, adults in summer-plumage, 

 we find that the length of the first primary coincides with 

 the power of flight of the species. All the species we arc 

 here concerned wath live in the open veld, and they have 

 therefore a short primary less than half the length of the 

 second. As there is also a difference in the length of the 

 tiiil as compared with the wing (though this may not have 



