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There is a growing body of evidence that maternal antibodies transferred to offspring have potential implications in the evolutionary ecology of birds. This transfer of maternal antibodies is a potentially flexible mechanism of non-genetic inheritance by which mothers could favour some offspring over others and/or increase offspring survival, but this is a phenomenon that remains poorly understood. We examined sex-specific deposition of maternal antibodies and its effects on early (5 d) and fledging (17 d) survival in semiprecocial chicks of the gull-billed tern Gelochelidon nilotica, a long-distance migratory bird. Mothers transferred a significantly greater amount of maternal antibodies to sons than to daughters. We found evidence for positive associations between maternal antibody levels at hatching and early offspring survival. This association might be sex-specific, which can be understood as a mechanism of parental favouritism for the most sensitive sex.