NEST VENTILATION EXPLAINS GAS-COMPOSITION IN THE NEST-CHAMBER OF THE EUROPEAN BEE-EATER

The European bee-eater Merops apiaster builds a nest in soil banks comprising a horizontal corridor (159 cm) leading to a 3.4 L nest chamber. An adult and six eggs and/or nestlings occupy this nest for 60 d. Incubation and development are asynchronous. In order to evaluate the gas exchange pattern of the occupied nest, we measured the O2 diffusive conductance of the nest with the ambient environment (GN(O2)), its internal O2 and CO2 pressures (PN(O2) and PN(CO2)), temperature (TN) and observed the sequences of development and the frequency of parental visits. We also measured the rate of O2 uptake (M(O2)) of the eggs, nestlings and adults. The GN(O2) was 10.9 MI[STPD]/(h . Torr). The PN(O2) dropped and the PN(CO2) increased during incubation and growth to a maximal change of 24 and 23 Torr, respectively. Maximal M(O2) of an egg and a nestling were 5.4 and 146 ml[STPD]/h, respectively. The M(O2) of an adult at rest and at TN (27-degrees-C) was 90.5 ml[STPD]/h. From clutch size, sequence of nest events, and the above values we have estimated a maximal nest chamber ventilation (VN) of 0.8 L/min necessary to prevent lowering PN(O2) to 74 Torr below ambient P(O2). This convection is achieved chiefly by the parental feeding visits (up to 40/h). Thus, movement along the corridor convects 1.2 L per visit.