Page:The British Warblers A History with Problems of Their Lives - 6 of 9.djvu/35

 unusual to find a late second brood in the case of this species, and the fact of the first female building a third nest points in the same direction, and is evidence of expectation on her part. Failure, however, was the result, brought about, I believe, solely by abnormal conditions.

I have not yet noticed any striking variation in the duration of the period between the arrival of a female in a given territory and the laying of the first egg. So far as my observation goes this period is from seven to nine days, but since there is considerable variation in this respect in the case of other species, it is possible that it is really greater than the above figures represent it to be.

The female commences to build about two days after her arrival. Deducting these two days from the normal period of fertilisation, which is approximately eight, we get six days for the actual construction of the nest. This need not necessarily, and probably does not, represent the building capabilities of the bird; for with regard to rapidity of construction the female must be guided by the development of her ovaries. It will be remembered that the first female in No. 2 territory constructed her second nest in less than four days, and the second female her one nest in less than three. Under ordinary conditions a female builds rapidly for a short time and then ceases, and the greater part of the work seems to be done during the first few hours of daylight, for, before leaving a territory, I have taken particular notice of the details of a certain nest, and upon arrival the following morning have found nothing added thereto. The greater part of the actual construction is the work of the female, the male seldom, if ever, attempting to share this duty with her, but it is no uncommon occurrence for him to interrupt the process by flying at her and pursuing her through the bushes. Sexual desire is the cause of this, as it is the period of fertilisation. Although dead grass and dead leaves are made use of to a large extent in the construction of the nest, it is worthy of notice that in many instances the bark of the honeysuckle is utilised,