Breeding ecology of ground tits in northeastern Tibetan plateau, with special reference to cooperative breeding system

Data on breeding ecology of a color-band marked population of the ground tit Parus humilis were collected in north Qinghai on the Tibetan plateau, during 2008 and 2009. In spring the birds excavated 0.8−3.2 m long nesting burrows under the ground. First-egg laying occurred between late April and late June during which a pair produced one brood. Incubation was done by female alone for 15−16 days and nestling-feeding by both sexes and helpers in any for 23−25 days. Average brood size at fledging was 5.8 (± 1.4 SD, 3−8) and all the 27 observed nesting attempts fledged at least one young. At the population level, brood sex ratio did not differ from 1:1. The birds are a territory-living resident, with annual resight rates being 48% (22 of 46) in adult breeders and 10% (7 of 67) in yearlings. Pairs were socially monogamous, of which 23% (9 of 40) contained one and some- times two male helpers, most likely being philopatric sons of the breeders. The formation of cooperative groups is similar to the population in central Tibet but differs from that in south Guansu where breeding ground tits exhibit a high level of annual turn- over (Current Zoology 57 (6): 751-757, 2011).