Page:The British Warblers A History with Problems of Their Lives - 5 of 9.djvu/51

 for possession would lead to available breeding ground remaining untenanted. For a male when seeking a territory will settle by chance in a certain place, and finding it already occupied, will struggle with the owner, and perhaps be defeated, or quietly pass on. In either case it may lay claim to adjacent unoccupied land, but it is not unlikely, especially after a fierce encounter, that it will be only too anxious to abandon that immediate district, thus leaving available ground in its rear unoccupied. Every male will not be compelled to struggle each season for its territory; it is clearly impossible that it can be so. On the other hand, if every male has always equal chances of securing a territory, and thus attaining to reproduction, no elimination can take place and no beneficial results can accrue to the species. But this will not be the case; competition will vary in different species, will vary in different seasons, and even in the same species will vary in different districts, according to changes of environment and the rate of increase. The weaker males will often reproduce, but, taken over a number of years, the stronger will reproduce more often than the weaker, and this is all that is required by the theory.

When we consider all of this, and at the same time bear in mind that the reproductive instinct is possibly not so strong in one male as in another, so that in the former case it may soon become weary of seeking territory and be content to remain unobserved in a district already tenanted, we can understand that there must needs be a number of unpaired birds. The pool in front of my house is generally inhabited by one pair of Moorhens. One autumn both birds disappeared, the one some time after the other. The pool then remained unoccupied until the 16th of the following June, upon which date a single individual took possession. On July 13th a mate appeared, and they immediately commenced to build a nest, ultimately succeeding in rearing a small brood. If territory were not a necessity, why should these two solitary individuals of the opposite sex have waited till so late in the