90 SYLVIID.E. 
The Chiff-chafF is to be seen throughout the year in the 
Cork- wood, but is most common from November to March. 
I foand a nest on the 21st April in a bush about six inches 
from the ground. 
These four species of Phylloscopus all build domed nests, 
usually on the ground, but occasionally in bushes or fern at 
an elevation of sometimes two feet or more above the ground ; 
this is particularly the case with Bonelli^s Willow- Warbler. 
The Chiff-chaff is difficult to tell from the common Willow- 
Warbler, but is always smaller and the legs are darker, being 
almost black, the eyebrow is not so well defined, and it is a 
more dull-coloured bird than P. trochilus. The note is also 
very different and distinct. The young of all the species are 
more highly coloured than the adult bii'ds ; but the genus is a 
very troublesome and perplexing one to the student, and only 
to be elucidated by observing the different species in a wild 
state. The skins shrink and the colours fade so much that a 
cabinet naturalist is much the most puzzled with them. 
99. Hypolais polyglotta (Vieill.). The Yellow Willow- 
Warbler. 
" Arrives and crosses to Europe in April, returning in 
August and September, many remaining to nest around Tan- 
gier.^^ — Favier. 
This Willow- Warbler is exceedingly plentiful near Gibraltar, 
being one of the latest of the spring arrivals ; the first I ob- 
served was on the 25th of April, and the earliest date on which 
I saw eggs was on the 14th of May. The birds frequent trees 
and bushes, especially willows and sallows; and the nest, neatly 
built and cup-shaped, is in a great measure composed of sallow- 
cotton and thistle-down ; it is placed in bushes, and usually 
contains four pinkish-tinged eggs, marked with blackish 
spots. 
This bird was figured by Yarrell as the Melodious Willow- 
Warbler {H. icterina), a slightly larger species. The present 
bird is unknown in England, and has the first primary small, 
but longer than the primary coverts; in H. icterina it is 
scarcely as long. 
