The energetics of development in a very large altricial bird, the brown pelican

Abstract

The brown pelican, Pelecanus occidentalis, is the largest altricial species for which the energetics of embryonic development has so far been reported.

The brown pelican produces a relatively large chick from a relatively small egg (80–105 g) when compared with other altricial species. A normal clutch of three eggs is equal to less than 8% of the average adult mass (3500–2800 g). External pipping occurs on day 29 and hatching occurs on day 30.5. The mass at hatching is ~72 g, of which about 10 g is yolk retained in the abdominal cavity.

Embryonic development does not follow a simple exponential curve; daily relative growth rate diminishes throughout incubation. Water vapor conductance of the egg, 16.76 mg d⁻¹ · torr⁻¹ is somewhat larger than predicted on the basis of egg mass.

${\dot V_{{o_2}}}$ increases steadily throughout incubation but the rate of change diminishes from about 40% · d⁻¹ on day 8 to about 10% · d⁻¹ on day 26. The total energy expenditure through hatching is about 121 kJ of which the process of hatching uses about 3 kJ.

The pattern of embryonic development in brown pelicans is different enough from that in other orders to be consistent with the hypothesis that avian altriciality is polyphyletic.