37 
HOUSE MARTINS AS BUILDERS. 
By HENRY J. SLACK, F.G.S./Sec. R.M.S. 
T HE popular notion that all nest-making birds work by 
instinct, neither controlled nor modified by reason, has 
not been accepted by many distinguished observers, and has 
been demolished by Mr. Alfred Wallace, who supplies abundant 
reasons for his opinion u that the mental faculties exhibited by 
birds in the construction of their nests are the same in kind as 
those manifested by mankind in the construction of their 
dwellings.”* If it is said that birds are accustomed to do the 
same things in the same way, over and over again for years and 
generations, it should be remembered that this is also true of 
many races of men, and, to some extent, of all men. Such 
propositions are only true in a broad and general sense, and it 
is probable that a great many exceptions would be found 
amongst building birds if they were carefully looked for. After 
any building creature has formed a habit of constructing its 
abode in a particular way, it will most likely continue it until 
some change of circumstances renders it impracticable or 
inconvenient, and then whatever powers of reason and observa- 
tion it possesses will be exerted to get over the difficulty by 
some alteration in the material or the plan. 
Some time ago, M. Pouchet, of Rouen, noticed that the 
swallows of the present day, inhabiting that picturesque city, 
had a better pattern for their nests than those of older date 
which had been preserved in the museum. The new con- 
struction is more roomy than the old. Here, then, is a proof of 
divergence from any supposed “ instinctive ” pattern, and it is 
not likely to be a solitary exception. 
During the last three or four years the writer has noticed 
numerous divergencies and varieties in the nests made by house 
martins round his own dwelling. Instead of saying they 
all build alike, it would be much nearer the truth to say that 
each pair have their own notions on the matter, and vary them 
Intellectual Observer,” vol. xi. 420. 
