Individuals frequently leave home before reaching reproductive age, but the proximate causes of natal dispersal remain relatively unknown. The social cohesion hypothesis predicts that individuals who engage in more (affiliative) interactions are less likely to disperse. Despite the intuitive nature of this hypothesis, support is both limited and equivocal. We used formal social network analyses to quantify precisely both direct and indirect measures of social cohesion in yellow-bellied marmots. Because approximately 50 per cent of female yearlings disperse, we expected that social relationships and network measures of cohesion would predict dispersal. By contrast, because most male yearlings disperse, we expected that social relationships and cohesion would play a less important role. We found that female yearlings that interacted with more individuals, and those that were more socially embedded in their groups, were less likely to disperse. For males, social interactions were relatively unimportant determinants of dispersal. This is the first strong support for the social cohesion hypothesis and suggests that the specific nature of social relationships, not simply the number of affiliative relationships, may influence the propensity to disperse.

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A free-ranging juvenile California sea lion ( Zalophus californianus) stranded on the coast of Vancouver, British Columbia, with signs of lethargy and emaciation in April 2016. An asymmetrical skull with a prominent superficial cervical lymph node was found on initial assessment. Fine-needle aspirates and biopsies of the lymph node were consistent with neoplasia and the animal was humanely euthanized and presented for necropsy. A metastatic parotid gland adenocarcinoma was diagnosed with regional lymph node and pulmonary metastases. Local invasion of contiguous skeletal muscle, bone, ear, and tonsils was extensive and likely accounted for the unilateral craniofacial deformity. Neoplasia of nonurogenital origin in juvenile California sea lions are reported infrequently. This is the first case of a parotid carcinoma in a California sea lion.