An Experimental Test of the Effect of Diet on Preen Wax Composition in New Zealand Silvereyes (Zosterops lateralis)

Abstract

Most birds have a uropygial gland, which produces preen wax that birds spread over their feathers when preening. Preen waxes contain a variety of volatile components which may function, in some species, as signals to communicate identity of mates and nest sites, or provide information about the owner’s state. Such signals may not be reliable if preen wax composition is readily altered by changes in diet. We used a diet supplementation experiment in a New Zealand population of silvereyes, Zosterops lateralis, to determine if preen wax composition varied with diet. During the austral breeding season, free-living silvereyes were fed a mix of animal tallow ad libitum for a period of 22 days. Their preen waxes were collected 6 and 7 days (sampling period 1), 11 days (sampling period 2), and 21 and 22 days (sampling period 3) after the beginning of the diet supplementation to determine if preen wax composition would change in response to the addition of the supplemental food. Birds sampled within a 7-day period leading up to the diet supplementation acted as controls. We found no significant changes in the preen wax throughout the study period. Feeding did not affect preen wax composition, and there was no change in preen wax composition among sampling periods. Date of sampling also did not affect preen wax composition during the period of the experiment. As the preen wax of silvereyes is known to change between non-breeding and breeding seasons, the lack of change in our study was not simply the result of preen wax production being fixed. Instead, our results support the hypothesis that preen wax composition in silvereyes is determined by endogenous mechanisms and is not affected by day-to-day variation in diet.