UC Berkeley

Aim: Terrestrial deposition of aerosol marine sodium declines with distance from coastlines. Salt deprivation in vertebrate herbivores and salt-seeking behaviours should hence increase with distance inland. We analyse published geospatial data on ungulate-patronized salt licks to test whether they are non-randomly distributed relative to distance from oceans and elevation. Location: Canada, Alaska and the contiguous United States. Taxon: Cetartiodactyla (even-toed ungulates). Methods: We determined the land area and median elevation of 100 km increments from the North American coast. The null model of the expected number of licks within each interval was determined by the ratio of the interval's land area to the total land area, multiplied by the total number of licks. We asked whether the number of licks further from coastlines was significantly higher than chance. We also assessed whether licks occur disproportionately at higher elevations, comparing the median elevation of observed licks to the median elevation within each interval. Results: We found a strong positive relationship between salt lick patronage by ungulates and distance from the coast. Licks occurred significantly less often within, and more often beyond, 500 km inland, and at significantly higher elevations than would be expected by chance. Main conclusions: These findings indicate that the patronage of salt licks is constrained geographically, and that the foraging behaviour of ungulates and other phytophagous vertebrate taxa may be influenced over large spatial scales by sodium availability. Salt-seeking behaviour varies on a wide biogeographical scale across North America, with concomitant implications for vertebrate herbivore behaviour and ecology.