The incubating behavior of the horned lark and small skylark was studied in alpine meadows. The key results are: ① There was no significant difference in the temperature outside the nests of horned larks and small skylarks ( F 1, 87 =3 286,P >0 05). ② If parents were off the nest, the temperature in the nest was not significantly different between the two species( F 1,87 =3 009,P >0 05), however, if parent birds were on the nest, the temperature in horned lark nests was significantly higher than that in small lark nests ( F 1, 210 =7 555,P <0 01). ③ Temperature trends inside and outside the nests of the two species were similar, both following a low high low, pattern and showed a significantly positive correlation(horned lark: r=0 572, n=158, P <0 01;small skylark: r=0 511, n=141, P <0 01). ④ During the hatching period, the temperature in nests was significantly higher than the outside temperature in horned larks( t=7 051, df=157, P <0 01), however, there was no significant difference between the inside and outside in the small skylark( t=-1 558, df=149, P >0 05). ⑤ The attendance time of horned larks and small skylarks showed three peaks; before 09:00 h, between 12:00 and 15:00 and after 19:00 h, respectively. ⑥ The attendance time and incubation behavior of the two species changed with variation in the environmental temperature. ⑦ There was no significant difference in the average attendance time per day between horned larks and small skylarks( P >0 05). ⑧ The attendance frequency of horned larks was high (4 17 times/h), and visit duration short (524 32 s/period), wherase small larks showed the opposite pattern; low attendance frequency(1 79 times/h)with relatively long( 1 510 00 s/ periods)visits. Our results are consistent with the hypothesis that attendance time is a balance between the energy requirements of the parent birds and the temperature requirements of the developing embryos. It follows that a birds choice of nest site should involve a trade off between costs and benefits, e.g. micro
