CHIFF-CHAFF 
This uniformity seems to extend to all the activities, 
whether referable to instinct or habit; but at the same 
time there are incidental details connected with them which 
vary in each particular case, and in what manner they are 
carried out can only be determined by each individual as 
the need arises. It is while performing these details that 
I have noticed a remarkable tendency towards the formation 
of fixed habits, a tendency to repetition. JI mention this here 
because it may bear some relation to the law of uniformity.’ 
It is of common occurrence in Nature. I have referred to 
it in the way in which the Chiff-chaff approaches the nest, 
but other birds have the same habit. When searching for 
materials to build their nests, birds frequently return to the 
same spot, although such material could be gathered more 
conveniently ; and in the same way they return again and 
again to the same place for food; the Great Spotted Wood- 
peckers (Dendrocopus major) are a good instance of this, 
for they often have their rounds, consisting of certain trees, 
which they visit in order daily; families of Tits also have 
their rounds. We find the same thing in the accurate 
measurements of periods of time, but more conspicuously in 
the way in which the same branch in a certain tree in the 
breeding territory is utilised as the headquarters. <A better 
illustration is the manner in which the same birds repeatedly 
return to the same situation for the purpose of breeding. 
A number of Martins (Chelidon wrbica) build against my 
house in such a position that their nests are washed 
away by any heavy rain, yet they return year after year. 
It is impossible to prove that the same birds return 
each year, but this is really unnecessary, since the nests 
d 
' Darwin refers to this tendency in the ‘‘ Descent of Man”’ as follows: 
«There seems even to exist some relation between a low degree of in- 
telligence and a strong tendency to the formation of fixed, though not 
inherited, habits; for, as a sagacious physician remarked to me, persons 
who are slightly imbecile tend to act in everything by routine or habit, and 
they are rendered much happier if this is encouraged.” 
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