Daily measurement of chick mass could be a useful method to estimate daily food intake under the assumption that the effects of the body mass on daily mass increment do not differ between chicks receiving different amount of food. To evaluate this assumption, 40g and 60g anchovy per day were fed to Rhinoceros Auklets chicks in semi-captivity. Negative relationships between chick mass and daily mass increment were found in 40g-and 60g-fed chicks. There was no significant difference in the slope of regression equation between 40g-fed chicks (-0.037±0.018) and 60g-fed chicks (-0.041±0.016). The intercept in 60g fed chicks (17.578±3.491g) was larger than that in 40g fed chicks (10.950±3.491g). Therefore, the daily amounts of food intake in Rhinoceros Auklet chicks can be estimated from body mass and daily mass increment.