[Objectives] Embryonic heart rate is an important life history trait in birds. Studying the embryonic heart rate and its correlation to egg mass will provide valuable knowledge to understand life history strategy. However, the information about the embryonic heart rate of tropical birds is still poorly known in China. [Methods] We investigated the embryonic heart rate of four bird species using Buddy Digital Egg Monitor around Nonggang National Nature Reserve in Guangxi, Southern China, from April to July in 2021. We used Independent Sample T-test to analyze the data of embryonic heart rates and fresh egg masses. Pearson correlation analysis was employed to analyze the correlation between daily growth of embryonic heart rates, heart rates at 80% of incubation days, maximum heart rates, and fresh egg masses. In addition, the correlation between daily growth of embryonic heart rates, heart rates at 80% of incubation days, maximum heart rates, and fresh egg masses in interspecific was determined by Power-Function regression analysis. [Results] Our results suggested that embryonic heart rates of Red-whiskered Bulbul (Pycnonotus jocosus), Yellow-bellied Prinia (Prinia flaviventris), and Yellow-bellied Warbler (Seicercus superciliaris) began to appear from the 4th day of incubating. The 4th-day heart rates were 157.9 ± 20.5 beats/min (Fig. 1a), 115.0 ± 48.5 beats/min (Fig. 1b) and 153.0 ± 11.7 beats/min (Fig. 1c), respectively. White-browed Piculet (Sasia ochracea)’s embryonic heart rate began to appear from the 5th day of incubating (152.6 beats/min) (Fig. 1d). With the increase of incubation duration, the embryonic heart rates of the four birds showed an upward trend in general (Fig. 1). Within three species of passerine birds, changes in daily growth of embryonic heart rates, heart rates at 80% of incubation days, and maximum heart rates were not significantly related to fresh egg masses (Table 1 and Fig. 2). There were no significant correlations between daily growth of embryonic heart rates and fresh egg masses among the four bird species (Fig. 3). [Conclusion] To summarize, our findings indicated that there was an interspecies negative correlation between egg mass and maximum embryonic heart rate at 80% of incubation in northern tropical limestone region, however, the intraspecific correlation between egg mass and embryonic heart rate was not significant.