The Breeding Ecology Of Brown-flanked Bush Warbler (Horornis Fortipes)

Brown-flanked Bush Warblers(Horornis fortipes)of the family Cettiidae and the order Passeriformes is one of the most common songbirds in subtropical forests in China.The breeding ecology of the Brown-flanked Bush Warbler,including nest-site choice,incubation and nestling feeding behavior During the breeding season from April to August 2017-2018 was investigated in Kuankuoshui National Nature Reserve,Guizhou Province,Southwestern China.A direct search method was used to find nests of the Brownish-flanked Bush Warbler in different habitats in the nature reserve.Nest parameters and nest-site characteristics were recorded and measured.Nests of the Brownish-flanked Bush Warbler were mostly in tea fields(71.6%),which was on average 38.47m SD=36.34m from roads and 13.07±11.32 m from forest edge,and nest height was 0.69±0.31 m(n=60 nests).The nest is in forest openings,woven from withered grass leaves and lined with chicken or bird feathers.The outer diameters of the nest was 11.26±2.74 cm,inner diameter 5.12±1.68 cm,and nest depth 5.45±0.86 cm(n=60).Comparison Brown-flanked Bush Warbler with Buff-bellied Willow Warbler(Phylloscopus subaffinis)breeding in the same tea fields,showed that nest sites of the two species differed significantly from each other.Nesting success of the Brownish-flanked Bush Warbler(35%,n=60)was significantly lower than that of the Buff-bellied Willow Warbler(59%,n=22).The breeding season of the Brownish-flanked Bush Warbler lasts from May to August,and clutch size is 3.38±0.81 eggs(n=56).Egg mass was 1.46±0.20 g,with egg length was 16.9±0.75 cm,egg width 13.1±0.75 cm and egg volume1.50±0.22 cm~3(n=148).There was no significant difference in chromatism and saturation of egg color between 2017 and 2018 in different habitats,but there was significant difference in brightness of eggs.Female Brownish-flanked Bush Warblers incubate alone according to video recordings.The incubation period lasts ca.10 days varying from 140 to 180 hours.The incubation frequency decreased with duration of the incubation days,while the time spent incubating increased with time.The Brownish-flanked Bush Warbler generally leaves nest for the first time around 06:00 and returns to nest around 19:30at the latest in the afternoon.The time of each nesting was 16.84±8.05 min,the sitting rate was 52.3±6.8%during the daytime,and egg hatching success was only39%(n=100 eggs).The Brownish-flanked Bush Warbler is the main host of the Lesser Cuckoo(Cuculus poliocephalus).We compared nestling growth and development of the Brownish-flanked Bush Warbler and the parasitic Lesser Cuckoo.The incubation period of the Brownish-flanked Bush Warbler was 13.6±1.4 days(n=3),while the Lesser Cuckoo needed 15-16 days for leaving the nest.The Brownish-flanked Bush Warbler fed its own nestlings 52.33±6.81 times per day,while Lesser Cuckoo nestlings were fed 45 times per day.The duration of the daily brooding period decreased with increase age of nestlings and warming of chicks ceased at the age of 7days.In the early stage of brooding(day 1 to day 4),the feeding rate by parent birds of the Brownish-flanked Bush Warbler was less than the feeding rate in the middle of the nestling period(day 5 to day 8),which was also the fastest period of growth and development.The feeding rate also increased during the late stage(day 9-day 12),of parent birds.Most nestlings were fed Lepidoptera(moths)and Orthoptera(grasshoppers).There were significant differences in body mass,body length,beak length,wing length and tail length between nestling warblers and cuckoos,while there was no difference in tarsus length.Fledgling Brownish-flanked Bush Warbler started to grow feathers at the earliest when 3 days old and tail feathers when 7 days old.The body weight at the time of leaving the nest was 8.52±0.98 g,and the body length was 62.86±5.26 mm.Nestling Lesser Cuckoos weighted 31.89 g and were 110.42mm in body length when leaving the host nest.