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).