Thousands of birds fill the air over Mono Lake, banking and swooping in a swirling murmuration that resembles an aerial school of fish. As they sweep past, their beating wings whoosh in unison. This small species, the Wilson’s phalarope, arrives from the north in large numbers each summer to feed at the saline lake, preparing for a long journey to South America. After spending July gorging on the larvae of alkali flies, the birds are gradually departing this month to begin their migration to another saline lake about 6,000 miles away — Laguna Mar Chiquita in Argentina. Partly because of their remarkable transcontinental voyage between salt lakes, the grayish birds have inspired a close partnership between communities in California and Argentina.