rings farther than is absolutely necessary, but will
pair whenever the opportunity for doing so arises, it is to the later
females, forced onwards by competition, that the late males must look
for mates; so that when at length pairing does take place, much valuable
time will have been lost.

The disadvantages which the late arrivals have to face are therefore
great, and it is probable that the percentage which attain to
reproduction will on the average be somewhat lower than the percentage
in the case of the earlier arrivals. The district in which my
observations have been made lies well within the limits of the breeding
range of most of our common species, and it is not surprising that I
should have met with little evidence of failure to breed as a result of
failure to secure territory. Some interesting information was supplied
to me, however, by the late Robert Service. He found, in certain seasons
in Dumfriesshire, flocks of from ten to fifty unmated Sedge-Warblers,
which, from the time of their arrival in May until the middle of July,
haunted reed-filled spaces along stagnant streams. These flocks appeared
to him to be composed of loosely-attached individuals of a migrant flock
that had failed to find things congenial enough to entice them to
disperse. But may they not have been composed of males that had failed
to secure territories, or of females that had failed to discover males
in possession of territories, or of both?

We have seen that, in the case of many species, each male establishes
itself in a particular place at the commencement of the breeding season,
even though this may mean a partial or perhaps a complete severance from
former companions. We must now discuss this fact in greater detail
because it is opposed to the views often held regarding the sexual
behaviour of birds, and is manifestly of importance when considering
the theory of breeding territory.

First, however, there is a point which requires some explanation. I
speak of the _same_ male being in the _same_ place. How can I prove its
identity? In the first place it is highly improbable that a bird which
roams about within the same small area of ground, makes regular use of a
certain tree and a certain branch of that tree, and observes a similar
routine day after day, can be other than the same individual. But, apart
from this general consideration, are there any means by which
individuals of the same species can be identified? Well, there