A Comparison of Vocalizations of Western Gulls (Larus occidentalis occidentalis and L. o. livens)

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Abstract
Two of the 3 recognized subspecies of the western gull (L. occidentalis) breed along the west coast of the USA and Baja California and closely resemble each other (L. o. occidentalis and L. o. wymani). The 3rd subspecies (L. o. livens), endemic to the Gulf of California, differs in several characteristics, including voice. Eight vocalizations of L. o. occidentalis were compared with L. o livens and long calls of all L. occidentalis subspecies were compared to species breeding to the north (L. glaucescens) and south (L. dominicanus). Vocalizations of L. o. livens are distinctive and further support its classification as a separate species. Long calls of L. o. livens are low pitched, presumably adapted for long distance propagation in a relatively quiet environment; L. o. occidentalis, L. o. wymani long calls have features that may facilitate their localization by receivers.