282 
Mr. Montagu's Observations 
conjecture, that naturalists, who have not had the opportunities 
of attending them in their native haunts, and have only examined 
a few individuals, perhaps in their extreme dissimilitude of plu- 
mage, might, without committing their scientific knowledge, de* 
scribe them as a distinct species. ]t must, however, be acknow- 
ledged, that the actual criterion is the tracing of such doubtful 
subjects through their several changes, from the nestling to the 
adult: such has been our usual plan where opportunity per- 
mitted. 
On the present question, were it not for the strong chesnut co- 
lour the Kentish Plover is said to possess on the crown of the 
head, as described by Lewin, and since by Dr. Latham in the 
Second Supplement to the General Synopsis, we should not have 
hesitated in pronouncing these three birds to be only one species; 
for the marks on which so much stress of discrimination and di- 
stinction is laid by some, particularly by the writers of a periodical 
publication, will by no means hold good, not only with respect to 
this, but also to many other species of birds, as we can prove from 
ocular demonstration. There is indeed nothing more vague and in- 
determinate than the colour of the legs and bill ; a circumstance 
that has led already to much confusion, and of which we beg 
leave to put the young and unexperienced ornithologist upon his 
guard. 
It would be endless to adduce instances of these uncertain 
marks, more or less changing by age and season, so well known 
to those who search for truth amongst Nature's native stores: 
the examples of the Black-headed and Herring Gulls, hereafter 
mentioned in this paper, are sufficient to show the care requisite 
in admitting the colour of those parts as the only specific di- 
stinction. 
The colour, therefore, of the head alone, in what is described as 
the 
