Breeding biology of two sympatric Aegithalos tits with helpers at the nest

Abstract

Although knowledge of breeding biology is fundamental for investigating the variation and evolution of avian reproductive strategies, research on Asian Aegithalos tits remains limited. The breeding biology of sympatric populations of Black-throated Bushtits (Aegithalos concinnus) and Silver-throated Bushtits (A. glaucogularis) was studied in the Dongzhai National Nature Reserve in central China from 2007 to 2010. Both species produced one brood annually. Clutch sizes, brood sizes and nesting success were not different between species. Parents of both species participated in all breeding activities, except for the male Silver-throated Bushtits, which were not involved in incubation. Cooperative breeding behaviours were observed in the studied populations of both species. Most helpers were found at the provisioning stage, during which time 1–2 helpers were present at 20% of Black-throated Bushtit nests (n = 50) and 30% of Silver-throated Bushtit nests (n = 40). All marked and confirmed helpers of both species were males. Compared with other Aegithalos species and populations, differences in either the occurrence of helpers or the proportion of nests with helpers indicate that the breeding strategies may vary with species and populations, and therefore, more efforts focusing on their basic biology and ecology are required.