EFFECTS OF CRUDE OIL EXPOSURE ON STANDARD METABOLIC RATE OF LEACH'S STORM-PETREL'

In a previous report (Trivelpiece et al. 1984), we noted decreased survival and reduced growth rate in chicks of oil-dosed adult Leach's Storm-Petrels (Oceanodroma leucorhoa). It was suggested that these effects were related to impaired ability of oil-dosed adults to provide food for their young, possibly due to elevated metabolic demands following contamination. We report here the effects of oil exposure on the standard metabolic rate of adults of this species using two different experimental methods. In the first experiment, the effects of oil exposure on adult petrels incubating eggs (20 to 40 days after laying) were assessed using a Scholander temperature-compensated respirometer. Petrels were captured in their nesting burrows during the day and were randomly assigned either to control or to one of two experimental groups. One experimental group (Internal Group) was fed 0.1 ml Prudhoe Bay crude oil (PBCO) with a stomach tube, while the other group (External Group) received an external application of 1.0 ml PBCO on breast and abdominal plumage via syringe. A gas chromatographic/mass spectroscopic analysis of PBCO has been reported previously (Peakall et al. 1982). Adults were weighed, oiled, and then maintained in artificial burrows for the duration of the experiment. The artificial burrows were 1-cm cylindrical cardboard tubes (length, 30 cm; internal diameter, 9 cm), with wire screen at one end for ventilation. Birds were maintained in a sheltered, heavily shaded area where daily temperatures ranged from 16 to 2 *C. When adult petrels were placed in the respirometryjars (4-liter), they were confined in small cardboard tubes (length, 20 cm; internal diameter, 6 cm) which were screened at each end. Soda lime was used to absorb carbon dioxide in the closed system, and the change in total pressure was tracked visually with a fluid-filled manometer. Oxygen depleted from the system by the bird was replaced via a syringe during a 30-min period, and oxygen consumption per hour was corrected to 0*C and 760 torr. Measurements of oxygen consumption were made about one hr prior to dosing and 24 hr after exposure. Following the experiment, adults were released into their breeding burrows. In the second experiment, adult petrels were captured in their burrows while they were brooding chicks (1 to 3 days of age). The petrels were maintained in cloth socks inside individual compartments in a cardboard box in a dark, cool basement (18 to 20*C) for the duration of this experimen . Birds were weighed and randomly assigned to control or experimental groups. Experimental birds were intubated with 0.1 ml of PBCO, and control birds were sham dosed without fluid. All birds were injected intraabdominally with 0.1 ml of water containing 95% atom % oxygen-18 and 98.8% atom % hydrogen-2 (deuterium) immediately after being dosed with oil. One hour after the injecti n, a blood sample was taken via a heparinized micro-hematocrit tube from the wing vein. Studies by Ricklefs and Williams (1984) have shown that one hr was sufficient for equilibrium to be established between the injected labeled water and the body fluids in the European Sta li g (Sturnus vulgaris). The birds were confined again, and a second blood sample was taken 24 hr later. The birds were then reweighed, sacrificed, and sexed by examination of reproductive organs. A 5-il blood sample was micro-distilled and hydrogen was produced by passage over uranium at 750*C. Hydrogen was collected for mass spectrometric assay by freezing ont activated charcoal at 189*C (Bigeleisen et al. 1952). Oxygen isotope measurements were made by converting blood samples directly to CO2 gas by reaction with guanidine hydrochloride using a technique described by Boyer et al. (1961), and more recently modified by Viglino et al. (1985). D/H and 011/016 ratios were determined by conventional isotope ratio mass spectrometry. Rates of CO2 production were calculated by the method of Nagy (1980). An examination of the data from the two experiments conducted in this study revealed apparently contradictory results. The mean (?SE) 0 hr standard metabolic rate (SMR) values for a group of 9 adults (2.1 ? 0.1 ml 02/(g h)-I and 24-hr values for the control group (2.4 ? 0.1 ml 02/(g.h)-1 in the respirometry experiment did not differ significantly from SMR values obtained for the treatment groups at 24 hr in this experiment (Table 1). By contrast, the mean SMR value calculated by changes in isotopic ratios during a 24-hr period was 3.7 + 0.4 ml CO2/(g-h)-I for control birds, which was significantly lower than the mean value of 4.6 ? 0.3 ml CO2/(g.h)-' for treatment adults (t = 5.361, P < 0.001). Differences in results obtained in the two experiments may reflect basic differences in the manner by which SMR was estimated by the two methods employed. The doubly labeled water method esI Received 30 April 1985. Final acceptance 20 January 1986.