(j I. r/i 
SOME OBSERVATIONS ON A TERN COLONY. 
By WILLIAM ROWAN. 
['he work of which this is a brief description was 
carried out, in 1913, on Blakeney Point, Norfolk. 
The idea was to determine, by means of a census, 
some of the laws that control the choice of site, 
nesting materials, and pigmentation of eggs. 
The work of previous years provided the basis 
for the methods employed. Many improve¬ 
ments in method suggest themselves, and future 
work should prove of decided value. This is the 
first systematic attempt at a census, to our know¬ 
ledge, and, though we know only too well the 
many weak points therein, we publish the results 
as much as a suggestion to ornithologists as for 
any other reason. The work involved is long and 
tedious, and results are few. 
Blakeney Point is a shingle spit of some eight 
miles in length. Its extremity projects freely into 
the sea. On the seaward edge of the terminal 
mile and a half there is a large open shingle beach ; 
further in are sand dunes, and on the landward 
side of these are salt marshes and mud flats. At 
high tide there are nearly two miles of water 
between these and the mainland. 
It was on the seaward side of the dunes on the 
open shingle that the famous old colony of Terns 
took up its quarters this year, though there were 
a score or so of nests on one of the laterals on the 
lee side of the dunes. It was on the open shingle 
that the census was taken. 
Before describing the results of the census a 
ienra/k on the movements of a Tern colony may 
not be out of place. It must not be imagined that 
because Terns come to the Point year after year 
therefore they choose the same part of it every 
time for nesting—far from it. Their choice varies 
considerably. A few years ago their favourite 
nesting site was on the lee side of the dunes. Now, 
however, this part is deserted. Last year the colony 
was concentrated round those dunes known as the 
Tern Dunes ; this year, however, it has spread 
right along the beach, and not a nest was found on 
the dunes proper, while last year a number were 
located there. Of course, we are only referring to 
the common Tern now. The erratic nesting habits 
of the Lesser Tern are well known. This bird, too, 
was found in considerable numbers. 
Two people only were at work, and the month 
was July, so that we got only the late birds and 
two hundred and three clutches in all. I Our method 
of procedure was this. We marked out certain 
well-defined patches of shingle and together 
examined these in strips, passing and repassing 
each other till the ground had been completely 
covered, when we moved on to another patch. 
Four measurements were taken of each egg : 
long and short circumference, length and breadth. 
These were taken for biometrical purposes, also 
the type of mottling and ground colour. Then the 
egg was numbered with indelible ink, so that it 
should not be dealt with again. The number in 
each clutch was then recorded and the type of nest. 
In all two hundred and three clutches were found : 
one hundred and nineteen of cne each, sixty-six 
of two each, eighteen of three each. Of these 
thirty were abandoned, and the eggs addled and 
partially buried. Of the clutches containing one 
egg each we have no proof as to how many con¬ 
sisted of one originally, or in how many cases the 
one was merely a remnant of a larger clutch. 
Three types of nests were taken : (1) No nesting 
materials and no hole (see Figure 46) ; (2) no nesting 
material, but hole scraped (see Figure 47) ; (3) 
materials used (see Figure 48). Of these the follow¬ 
ing number of nests occurred : 
Type. Number of Nests. 
1 . 18 
2 38 
3 . 120 
Of these at least thirty were abandoned. 
Of type 3 twenty-four were large, thirty-nine 
medium, and fifty-seven slight. The majority were 
made of dried Psamma and similar materials, but 
four were found in which shells and pebbles had 
been used, while one contained a large number of 
crab-legs. In the marshes the drift-line consists ot 
thousands of dead crabs (Care in us maenas), so that 
the supply was plentiful. One nest was made 
almost entirely of wood-chips (see Figure 49). 
Nine nests were found in growing plants of Arenaria 
peploides, and one in living Triliciim. Some had 
nests built, others not. 
The Common Tern is doubtless a lazy bird, for 
in the vast majority of cases nests of type 3 were 
on the drift-line, or some similar situation where 
material was plentiful. In two years only one nest 
was found on the drift-line without any material 
whatever. This was a clutch of three very dark 
eggs. Nests of a considerable size, far from the 
drift or other supply of material, were more plentiful 
but far from common. 
The next thing studied in great detail was the 
mottling. From the work of previous years a 
table of types was drawn up (see Figure 50). These 
were respectively called A—I. It should be pointed 
out that the size" and shape of the eggs on the figure 
have nothing whatever to do with the mottling, 
and will be referred to later. Type C was the 
* Blakeney Point Publication, No. 10. 
j The operations of measurement and recording were carried out in conjunction with Miss K. M. Parker, my colleague 
in the Blakeney Point Field Section for Faunistics. 
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