154 Huxley, Bird-ivatching and Biological Science. [April 



The fighting, finally, is very curious. There are a great many 

 warlike preliminaries, a good deal of sparring and feinting, but only 

 once in a long while any real hard fighting, such as many smaller 

 birds indulge in — Tits and Thrushes, for instance. The whole 

 business comes to be half ludicrous, half contemptible to watch. 

 Selous' idea is that it has degenerated from real fighting and is now 

 fixed as a ceremonial action. At any rate it appears never to 

 decide anything — nor does it seem to have any influence whatever 

 on the hens. In this species, then, we have a fine "expression of 

 emotion" in the shape of the Dance, but here it is confined to one 

 sex instead of existing in both, as in the Grebe. We have also a 

 Display as a direct stimulus to coition, and working out in such a 

 way as to make Darwinian Sexual Selection opera ti\'e; and we 

 have sham Fights, whose downward development has probably 

 gone hand in hand with the upward development of the Display. 



As a third, and again very different form of history, let us take 

 that of the majority of the Old-world Warblers (Sylviidse) so 

 thoroughly worked out by Eliot Howard ('07). These birds 

 include a number of famous European songsters, such as the 

 Black-cap, Garden Warbler, and Marsh Warbler. They are 

 mostly of very sober plumage, with little or no sexual dimorphism 

 (though to this the Black-cap is an exception). The majority of 

 the forms are migratory, and it is to these that we will confine our 

 attention. 



The course of events is similar in almost all the species. In 

 March and April the birds come over to England from the South, 

 in flocks and bands, which, following the river valleys, gradually 

 split up as they spread over the coinitry. The influx of migrants 

 occurs in successive waves, and an important point to notice is that 

 the arrival-period of any species takes a considerable time. The 

 average immigration period lasts for about four weeks, but in some 

 species it is only about three, while in others, like the Chiff-chaff 

 it may extend to seven (and in some species of the closely related 

 Turdidse, even to 9 or 10 weeks).* Nests with eggs are usually 

 found before the migration is complete. 



■ See Annual reports on the immigration of summer residents, published in Bulletins 

 of the Brit. Ornithol. Club from 1906 onwards. 



