| Breeding ecology of animals is a basic but very important element of the life histories of animals, which are affected by environmental gradients (eg. altitude and latitude). The climate conditions in higher altitudes, leading to the different breeding traits of high-altitude animals, are unpredictable with stronger wind, heavier snow and stronger sun shine, lower temperature and less oxygen supply.In 2009 and 2010, we studied Tibetan ground tit (Pseudopodoces humilis), a passerine endemic to Tibetan plateau, in Anduo located in the northern Tibetan plateau with an average altitude of 4700 m above sea level. Our study included nest-site selection, breeding ecology, sex allocation and extra-pair parentage of the species and our main aim was to explore the adaptation of the birds to the harsh high-elevation environment. Our results were as follow:We studied eight factors influencing on nest-site selection of Tibetan ground tit by sampling spots. Stepwise discriminant function analysis was used to investigate nest difference among the plots (total 180 plots including 83 breeding and 97 random plots) to identify the variables of primary importance. Only three variables (habitat type, slope aspect and vegetation) entered to the discriminant functions. These three variables had a high discriminant power in differentiating between used and random plots. Our results suggested that Tibetan ground tits preferred to warm and wind-avoiding sites for nesting in high altitudes, these may be an adaptation to the low temperature and strong wind in high altitudes.Results of our two-year study showed that the breeding period lasted four months with reproduction beginning in early May and ending up the breeding in early August. Mean clutch size was 5.25±1.14(range:3-9 eggs),mean egg weight was 3.57±0.12 g, mean length and width were 23.0±1.01 mm(21.12-25.84 mm) and 16.49±0.55 mm (15.17-19.94 mm), respectivly, Mean calculated egg volume was 3.17±0.17 cm3 incubation period was 16-17 days; Brood size at hatching were 4.98±1.18, hatching rate was 95.16±12.69%, Brood size at fledging were 4.13±1.51, fledgling rate was 83±23.88%, breeding success was 93.33%.In general, Tibetan ground tit yielded a balanced overall sex ratio of offspring and territory quality, coorperative status, breeding date and female body condition had no significant correlation with the sex ratio of offspring. These results suggested that the cooperative breeding of Tibetan ground tits may result from the difference in the sex-specific mortality before reproduction, but not from the sex ratio of hatched nestlings.Through investigating the extra-pair parentage of 150 nestlings in 34 broods, 35.3%of which included at least one extra-pair offspring and 14.7% of nestlings were identified as extra-pair offspring. EPO referred to 9.6% of nestlings in 22.2% of bi-parental broods, and 85.7% of cooperative broods had a EPO level of 30.6%. The results from this manuscript also showed that relatedness and heterozygosity of social mates cannot explain the occurrance of higher level of extra-pair paternity. The underlying mechanism of EPP in Tibetan ground tits may be explained by the fact that the family structure with weak site philopatry and territoriality provid high opportunity for extra-group copulations.
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