Influence of egg oiling on colony presence of ring-billed gulls

Abstract

Egg oiling is a form of management in which bird eggs are coated with mineral or corn oil, preventing gas exchange through the shell and killing embryos. Unlike other nest- disturbance techniques, egg oiling reportedly precludes colony abandonment and, thus, can be advantageous when managers wish to limit dispersal within the breeding season to other locations while stabilizing the population or reducing productivity. However, unintended, indirect effects of egg oiling are not well-characterized. We evaluated the influence of egg oiling on ring-billed gulls (Larus delawarensis) within the Lake Champlain basin, Vermont, during the nesting season to determine whether egg oiling affected colony presence of adults. We radio- marked 58 ring-billed gulls captured on Young Island during 2008 to 2009 and treated all ring-billed gull nests in the colony with egg oiling except for 50% of the nests of radio-marked gulls (control group). Using a radio receiver with automated data logger, we documented the presence of ring-billed gulls at the colony throughout the breeding season. We examined effects of treatment (nests oiled or control), sex, reproductive period (pre- and post-hatch), year, and interactive effects on colony presence (i.e., the proportion of nights ring-billed gulls spent at Young Island). Although we found no effect of treatment, sex, or interactive effects on colony presence, colony presence was 87% greater in the pre-hatch period, presumably due to behavioral mechanisms related to incubation or foraging. Overall colony presence was 118% greater in 2009 than in 2008, potentially a consequence of increased colony disturbance in 2008. We suggest that egg oiling does not influence colony presence of ring-billed gulls within the breeding season.