TRANSACTIONS OF THE SECTIONS. 121 
Remarks on the Migration of Birds. 
By Curusert Cotiinewoon, M.B., M.A., P.LS., Lecturer on Botany at 
the Liverpool School of Medicine. 
The author began by remarking upon the extreme interest of the phenomena of 
migration to the ornithologist, and the simplicity of the general plan, which had been 
unnecessarily complicated by the supporters of the now exploded doctrines of hy- 
bernation and submergence. The fact that those birds which wiater here (except 
in those very rare cases which prove the rule) never breed with us, is the true key 
to those phenomena. The fieldfare and redwing are impelled northward in April, 
by the same impulse which brings the nightingale and blackcap to us from the South. 
All retire from the advancing sun in spring; and all seek those spots where they 
themselves first saw the light, there to rear their young. This business ended, they 
again retire to regions more constitutionally fit for them in the dead season. The 
sun, therefore, is the great moving power, and the equinoxes the signals for migra- 
tion. A sexual impulse, arising from the development of the reproductive organs, 
drives them before the advancing sun in spring,—a failure of temperature and food, 
added to that of the reproductive stimulus, makes them follow, the retiring sun in 
autumn, The author suggested, arguing from the analogy of the short internal mi- 
grations of some British birds, that the period of time during which a bird remains 
in this country in summer might be taken as an index of the distance southwards to 
which he retires for the rest of the year,—that the chiff-chaff, for example, which 
spends fully six months of the year with us, retires toa much less distance in winter 
than the swift, which remains absent from us nine months out of the twelve. The 
conditions under which birds exist in warmer latitudes in the winter season, are 
probably the same as regulate those which remain, the only difference being one of 
constitution or hardihood; that is, that our birds of passage require the higher tem- 
perature, simply to keep them in the same state of active life which our indigenous 
birds maintain under our wintry skies. As an example of these conditions, the fact 
that, of our migratory birds, the males arrive usually a week or ten days in advance 
of the females, seems to show that a separation of the sexes takes place with them, 
such as is so common a phenomenon with our indigenous birds at that season. 
That the migratory birds arrive in full song, the author was convinced from obser- 
vation, it having frequently happened that a careful watch for their first appearance had 
been rewarded at length by hearing just so much of their note as was sufficient for 
one well-acquainted with it to recognize them ; but on the following day the woods 
were resonant with the perfect notes of the very same bird. The recurrence of this 
observation had convinced him that fatigue alone had been the cause of their muti- 
lated song the previous day. Attention was next directed to the great discrepancy 
which existed between the mean date of arrival of the summer birds of passage, as 
given by different ornithologists. The mean dates given by White, Markwick, Jenyns 
and another for twenty-five summer birds of passage were presented in a tabular 
form, and exhibited a variation of as much as a month or six weeks for the same bird. 
This arises probably from the fact, that the experience of a single individual is liable 
to fallacy,—that he may not have the same opportunities of accurate investigation 
in two consecutive years: consequently, certain dates in a series of observations are 
much too late; and these, when reduced to a general mean, destroy the balance of 
the whole. A comparison of the earliest dates given by seven ornithologists, for the 
same twenty-five birds, gave much more equable results, because probably that 
observation was made under the best circumstances, and therefore most in accord- 
ance with truth. Still, however, there was something to be accounted for,—some 
influence which in certain seasons somewhat accelerated them, and in others retarded 
them. The question arises, whence does this influence arise? Surely not at the 
point for which they are making, but rather at that from whence they are setting out. 
We should not expect, therefore, that birds would necessarily arrive sooner in a for- 
ward season, nor later in a backward one; and experience proves, what reason would 
suggest, that the actual temperature of our spring is not intimately connected with 
the earlier or later appearance of the migratory birds. The author, however, pur- 
posed making a more careful comparison between the records of the arrival of the 
birds, and the meteorological indications, than he had been able to do hitherto, with 
