The foraging behavior of gerbils reveals the ecological significance of crude oil pollution

Despite extensive ecotoxicological evidence on the adverse effects of oil pollution on rodents, little is known about how rodents make decisions in oil-polluted environments (i.e., outside of lab settings). We investigated the foraging behavior of Allenby gerbils, Gerbillus andersoni allenbyi (GA), that were presented with feeding trays in a semi-natural environment. The trays contained seeds mixed into one of three types of soils – clean soil, and two different soil samples collected from two well-documented terrestrial oil spill sites in Israel. The oil spill disasters occurred in 1975 and 2014 and the spill sites are located within a few hundred meters of each other, in the 'Avrona Nature Reserve in the Arava hyper-arid region in Israel. Gerbils of both sexes avoided foraging in 2014-polluted soil, but surprisingly, they foraged more in 1975-polluted soil. Our results indicate that for the GA, the 1975-polluted soil is an advantageous substrate to forage on, probably because its texture facilitates more efficient foraging, leading to greater energetic gain, and creating a trade-off between energetic gain and perceived foraging cost due to its pollution. We also proceeded to investigate some physiological consequences of chronic exposure to the 2014-polluted soil in the laboratory. Chronic oil exposure did not lead to mortality or weight loss, but female gerbils exhibited heightened cortisol. We conclude that terrestrial oil pollution may have significant sublethal impacts on animal behavior, even when there is no obvious short-term physiological cost to the exposure.