 The red warbler breeds primarily in early spring , from February until May , though at least one nest containing young has been found as late as the end of June . The female alone builds the nest , a task which typically takes 4 – 6 days . She chooses a sunlit area , such as an area of windfall , the brushy edge of a trail or water course , or a small clearing , for its location . Tightly woven of plant material , the nest is hidden in ground vegetation and anchored to the stalks of surrounding vegetation . Bulky and untidy on the outside , it is typically constructed primarily of dead pine needles and dead grass , though gray lichens , green moss , dead leaves , shreds of bark and tips of fern fronds are also used ; most of these materials are gathered from the ground close to the nest , though some is picked from low branches or further away . The nest , which is usually oven @-@ shaped with a side or upward @-@ facing entrance , measures roughly 6 in ( 15 cm ) wide by 7 in ( 18 cm ) long by 4 @.@ 5 in ( 11 cm ) high . A small number of nests are only cups , lacking the roof of the more typical structures . Inside , the nest is tidy and compact , lined with fine grasses and plant fluff , which is generally gathered some distance from the nest . 
