3.4. Foraging energetics in shallow and deep waters
Despite the distinct behavioural profiles in different habitats (Fig. 4), the M. squamatus showed similar foraging energetics (Fig. 6), suggesting that the birds can fish equally efficiently in both deep and shallow waters. The estimate of mean net energy gains were 6.53 KJ/min and 6.28 KJ/min in deep and shallow habitats, respectively, and the standardized errors (SE) was comparably small (less than 0.50 in both habitats, Fig. 6A). Energy gains through food intake were slightly higher in deep waters (mean estimates were 6.99 KJ/min and 6.08 KJ/min in deep and shallow waters, respectively, Fig. 6B). Again, SE was small in comparison with the mean. The small SE suggested that the bird performed stably during the three winters in both habitats. Although the foraging energy costs were significantly higher in deep waters, this difference did not affect the comparison of energy balance as they were only a fraction of energy gain through food intake (generally less than 5%, Fig. 6C).