le is more than probable, but that this explains the
behaviour in question I do not believe. One wants to know why the
changes should occur earlier in the male, what disposition it is which
first comes into functional activity, and to what such disposition is
related.

It may, however, be urged that, after all, this apparent eagerness to
reach the breeding grounds is but a modification of hereditary procedure
under the guiding hand of experience. What more likely result would
follow from the enjoyment associated with previous success in the
attainment of reproduction than a craving to repeat the experience? What
stronger incentive to a hurried return could be imagined? It must be
admitted that there are certain facts which might be used in support of
an appeal to experience as a reasonable explanation. For example, the
first males to arrive often display that richness of colouring which is
generally supposed to indicate a fuller maturity. Gaetke even speaks of
the "most handsome old birds being invariably the first to hasten back
to their old homes." But if experience is a factor, if some dim
recollection of the past is held to explain the hurried departure of the
male migrant, one wants to know with what such recollection is
associated. Is it associated with the former female, or with the former
breeding place, or with both? I take it that any recollection, no matter
how vague, must be primarily associated with the particular place
wherein reproduction had previously been accomplished; and I grant that
if the first individuals to appear were invariably the older and
experienced birds, their early return might be explained on the basis of
such an association. But if there is reason to believe that a proportion
are young birds on the verge of carrying out their instinctive routine
for the first time, then we cannot appeal to past experience in
explanation of their behaviour.

The age of a bird is difficult to determine. Experience leads me to
believe that some of the males that arrive before the females are birds
born the previous season; one finds, for instance, individuals with
plumage of a duller hue, which denotes immaturity, amongst the first
batch of arrivals. But though plumage may sometimes be a satisfactory
guide, yet to rely upon it alone, or upon a more perfect development of
feather, is to exceed the limits of safety. How, then, can we ascertain
whether all the males that arrive before the females have had s