Blackcap and a Lesser Whitethroat, or between a Garden-Warbler and a Blackcap, but it is of short duration and lacks vigour. Apart, however, from such temporary disturbances, there is no real rupture in their relations, and certainly nothing to lead one to suppose that the bickerings are determined by the functioning of any~ specific instinct. Yet only a few months previously some of them were constantly at war, and their quarrels betrayed symptoms of great persistence; and if we remember how the observed behaviour of the birds suggests the fact that they were striving to attain something definite, we shall understand the nature and extent of the change, and shall, I fancy, be in a better position to estimate its biological worth at its true value.
We can find many similar examples—flocks are to be found on arable ground, on the water meadows, and on the mud-flats; here different kinds of Thrushes feed on the berries of the yew, there different kinds of Tits travel together in parties; hosts of Finches collect in the hollies to pass the night and Buntings roost together in the gorse; and, in fact, in whatever direction we choose to look in the autumn and winter, we find various birds assembled together and living on amicable terms. All of this changes in the spring, and the relationship undergoes a gradual but noticeable alteration; so much so that whereas the outstanding feature of bird life in the winter is sociability, that of the spring is hostility.
