Diurnal brooding behavior of long-tailed tits (Aegithalos caudatus glaucogularis)

Brooding is a major breeding investment of parental birds during the early nestling stage, and has important effects on the development and survival of nestlings. Investigating brooding behavior can help to understand avian breeding investment strategies. From January to June in 2013 and 2014, we studied the brooding behaviors of long-tailed tits (Aegithalos caudatus glaucogularis) in Dongzhai National Nature Reserve, Henan Province, China. We analyzed the relationships between parental diurnal brooding duration and nestling age, brood size, temperature, relative breeding season, time of day and nestling frequencies during brooding duration. Results showed that female and male long-tailed tit parents had different breeding investment strategies during the early nestling stage. Female parents bore most of the brooding investment, while male parents performed most of the nestling feedings. In addition, helpers were not found to brood nestlings at the two cooperative breeding nests. Parental brooding duration was significantly associated with the food delivered to nestlings (F=86.10, df=1, 193.94, P<0.001), and was longer when the nestlings received more food. We found that parental brooding duration declined significantly as nestlings aged (F=5.99, df=1, 50.13, P=0.018). When nestlings were six days old, daytime parental brooding almost ceased, implying that longtailed tit nestlings might be able to maintain their own body temperature by this age. In addition, brooding duration was affected by both brood size (F=12.74, df=1, 32.08, P=0.001) and temperature (F=5.83, df=1, 39.59, P=0.021), with it being shorter in larger broods and when ambient temperature was higher.