BRITISH WARBLERS
to show something more than mere passion, but, on the other hand, the negative evidence—that of the callous behaviour of the males, except during the period of sexual passion, of the desertion of the female by the male directly the young are able to take care of themselves, of polygamy, and of the replacement of a lost mate again and again in an incredibly short space of time—is so strong that it precludes the possibility of the existence, in at least a large majority of the cases, of any feeling beyond a momentary passion.
The nest is always placed low down amongst the bushes and undergrowth, holly, elder, or bramble being favourite resorts, but many other shrubs are utilised, and it is sometimes even suspended, after the same manner as that of the Reed-Warbler, from three nettles (Urtica dioica). In its construction dead grasses of different sizes are principally used, the coarser ones on the outside and the finer ones in the interior, the lining being of horse-hair. The female does the greater part of the building; the male sometimes helps independently, often singing when doing so, and at other times follows her closely as she searches for material, or watches her vigorous efforts to sever the various grasses, the fixing of which grasses takes considerable time. They shape the nest with their breasts by lying in it and turning round, and if the male happens to be at work when the female arrives, he immediately gives place to her. An inquisitive Chiff-chaff sometimes comes to watch the proceedings, but is immediately pursued. Outbursts of excitement are of common occurrence with the male, and he then pursues the female, erecting his feathers and flapping his wings.
Directly the first egg is laid the male takes his turn in sitting on the nest; and in cold seasons, especially in the mornings, the eggs are never left long exposed, one or other of the birds always showing anxiety to return. Now the time that they leave their eggs exposed, either previous to or during incubation, appears to vary with the prevailing conditions of the atmosphere. This procedure must be congenital, for how
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