318 INTRODUCTION TO NATUHALIST^S CALENDAR. 
place by a loss of some parts of a feather, thereby bringing into view 
some other portion, and so producing a different tint ; in others, the 
colour of the feather entirely changes. These variations take place 
more or less rapidly with the seasons ; but in some instances, the 
change is eflfected in a day or two, as in many of the plovers and sand- 
pipers, some ducks, and the head of the black-headed gull, &c., so that 
exactness in the registration of these changes should be observed. 
Some of our summer visitants assume their breeding dress after arrival 
here, while others are partially changed, as if the operation had 
commenced, and was going on at the same time with the instinctive 
desire to migrate. And again, on the cessation of the duties of the 
male, does the brilliancy begin to fade, and the dark or rich contrasted 
tints to blend into a plumage broken and worn, and now commencing 
to be renovated by a new moult — all these mutations are worthy to be 
noted, and can be easily done at the same time that other facts are 
registered. 
It is during this same important period that a great change periodi- 
cally takes place in the song and voice of birds. Many species sit and 
utter their call from some selected spot, which is frequented day after 
day ; but others practise peculiar modes of flight, calling as they fly. 
The pleasing song of our warblers and thrushes, the call of the pigeons 
and cuckoo, are familiar examples of the first. The towering flight of 
the greenfinch, and the rise and fall of the pipits singing as they 
fly ; the drone and flight of the 'snipe, and the shrill whistle of the 
curlew, are examples of the combined exercise ; but in every species 
there is a change more or less marked, which will be easily seen and 
noted by a practised or willing observer. 
There is yet another point worthy of attention, that is, the change 
in the general zoology of a district or locality which has taken place 
within a limited period, by an alteration of its physical character; 
by improvement, cultivation, draining ; by planting and the increase of 
wood ; by the rooting out and destruction of copse or natural wood ; by 
the introduction of some particular trees or brushwood. All these 
matters have a much greater influence on animal life than is at first 
imagined ; and in the space of twenty or thirty years, we have seen the 
character of a locality almost changed, by the forsaking of some species, 
and the coming in of others. These changes go gradually on, but are 
at last complete, being naturally incidental to the artificial causes 
above-mentioned. 
