68 
TERNS AT THE FARNE ISLANDS. 
they are usually alike both as regards size, shape, and 
colouring. I have not been able satisfactorily to ascertain 
the exact time of incubation, but think it is about sixteen 
days. The young as soon as they are hatched creep in 
amongst the Sea Campion for shelter, and you might often 
wonder what had become of the young birds, unless you 
knew where to look for them. 
The principal breeding place of S. liirundo is the “Knoxes,” 
an island formed of water-worn boulders and shingle, with 
fine sand in the centre, and entirely destitute of vegetation ; 
also the AVide Opens and the “ Northern Ears,” which 
last is only bare whinstone, with sand thrown upon it in 
patches ; a few pairs only form this colony. 
The nest is merely a slight hollow scratched by the bird in 
the shingle or sand without the slightest signs of any lining; 
a favourite site being just above high water mark on the 
pebbly beach. The eggs are two in number (rarely three), 
usually very dark in ground colour and markings. I have 
never verified a nest with three eggs as belonging to 
8. liirundo; all those with that number have turned out 
to belong to 8. fluvicitilis. 
My observations have led me to the following conclusions 
concerning the difference between S . Jiuviatilis and 8. hirundo. 
In the adult bird, S. fluvicitilis is lighter in colour, especially on 
the breast, and slightly larger ; the tarsus is longer, and this 
mark of distinction I hold to be an infallible test, and 
discernible in all stages; the wings also extend beyond the 
tail; while in the case of hirundo the reverse occurs. The 
nest of duviatilis has a slight lining and is placed generally 
amongst some kind of vegetation, and some distance from the 
shore, the number of eggs being frequently three ; whereas 
the nest of hirundo has no lining and is usually placed 
amongst stones and shingle, often only just out of reach of 
the tide, the number of eggs being usually two. The young 
of these two species differ little when first hatched except 
that those of hirundo are darker and have a smutty appearance. 
The method I adopted to verify the eggs was to snare the 
old birds at the nest, which can easily be done; and after 
determining the species I liberated the bird, as the mode 
of capture does not injure it in the least. Some years ago, 
when I wanted specimens, those so caught were killed, and 
five-sixths of them upon dissection proved males, clearly 
showing that in the Sterninte the male assists in incubation, at 
all events during the day. 
8. douijalli, the most beautiful and graceful of all the 
Terns, occurs in small numbers, associated with S. fluviatilU 
