Cuttlefish can rapidly alter their appearance by using neurally controlled chromatophore organs. This ability may provide a window into their cognitive capacity. We test whether the changes in body pattern that occur during hunting depend on context. If they do, then it may be possible to use these changes to study cephalopod cognition while the animal is engaged in ecologically relevant tasks. We found consistent individual differences in the tendency of cuttlefish to hunt with the first two arms raised. We also found that cuttlefish usually darken their skin after they seize a prey item. This darkening is observed regardless of the identity of the prey (fish, crab, or shrimp), prey context (buried in sand, in a bare tank, or on top of a rock pile), or the presence of a sudden stimulus. The sudden stimulus was created by presenting an overhead model bird to the cuttlefish. The model induced components of the Deimatic Display, which is a form of antipredator behavior, suggesting that the model was perceived as a potential threat. Passing Cloud displays and the Darkening of the arms were significantly reduced after exposure to the model bird. The effect of a potential predator on body pattern expression during hunting suggests it may be possible to use these changes as a sensitive indicator of ecologically relevant learning.

Breeding at high elevations can favour life-history strategies in which parents shift to investing in higher quality rather than higher numbers of offspring. In American Dippers (Cinclus mexicanus Swainson, 1827), altitudinal migrants produce fewer fledglings than sedentary individuals (residents) that breed at lower elevations. We examined whether migrants compensate for their lower fecundity by providing their offspring with a higher quality diet and (or) more food, and producing higher quality offspring. Nestling diet was assessed using observations and stable isotope analysis of feathers grown during the nestling period. Nestling quality was assessed using a condition index (residuals from a mass-tarsus regression) and postfledging survival. We found that migrants fed their offspring less fish, and despite having higher feeding rates, had lower energetic provisioning rates than residents. Migrants also produced offspring that were in worse condition and had lower postfledging survival. This study found no evidence that altitudinal migration is associated with a trade-off favouring the production of smaller numbers of higher quality young. Instead our data provide support for the hypothesis that altitudinal migration in American Dippers is an outcome of competition for limited nest sites at lower elevations that forces some individuals to move to higher elevations to breed.Résumé : La reproduction aux hautes altitudes peut favoriser des stratégies démographiques dans lesquelles les parents investissent dans des rejetons de plus grande qualité plutôt que dans un nombre plus élevé de rejetons. Chez le cincle d'Amérique (Cinclus mexicanus Swainson, 1827), les individus qui migrent en altitude produisent moins de petits à l'envol que les individus sédentaires (résidants) des altitudes plus basses. Nous vérifions si les migrateurs compensent leur fécondité réduite en procurant à leurs rejetons un meilleur régime alimentaire ou un régime plus abondant et en produisant ainsi des petits de meilleure qualité. Le régime alimentaire des petits au nid a pu être déterminé par observation directe et par analyse des isotopes stables dans les plumes élaborées durant la période au nid. La qualité des petits au nid a été mesurée par un indice de condition (résidus de la régression de la masse sur le tarse) et par la survie après l'envol. Les migrateurs apportent moins de poissons à leurs rejetons et, malgré des taux d'alimentation plus élevés, ils ont des taux d'approvisionnement en énergie inférieurs à ceux des résidants. Les migrateurs produisent aussi des petits en moins bonne condition dont la survie après l'envol est inférieure. Notre étude n'offre aucune indication que la migration en altitude comporte un compromis favorisant la production de petits moins nombreux mais de meilleure qualité. Au contraire, nos données appuient l'hypothèse selon laquelle la migration en altitude chez les cincles d'Amérique résulte de la compétition pour un nombre limité de sites de nidification aux altitudes inférieures, ce qui oblige certai...

Studies of partial migrants provide an opportunity to assess the cost and benefits of migration. Previous work has demonstrated that sedentary American dippers (residents) have higher annual productivity than altitudinal migrants that move to higher elevations to breed. Here we use a ten-year (30 period) mark-recapture dataset to evaluate whether migrants offset their lower productivity with higher survival during the migration-breeding period when they occupy different habitat, or early and late-winter periods when they coexist with residents. Mark-recapture models provide no evidence that apparent monthly survival of migrants is higher than that of residents at any time of the year. The best-supported model suggests that monthly survival is higher in the migration-breeding period than winter periods. Another well-supported model suggested that residency conferred a survival benefit, and annual apparent survival (calculated from model weighted monthly apparent survival estimates using the Delta method) of residents (0.511 ± 0.038SE) was slightly higher than that of migrants (0.487 ± 0.032). Winter survival of American dippers was influenced by environmental conditions; monthly apparent survival increased as maximum daily flow rates increased and declined as winter temperatures became colder. However, we found no evidence that environmental conditions altered differences in winter survival of residents and migrants. Since migratory American dippers have lower productivity and slightly lower survival than residents our data suggests that partial migration is likely an outcome of competition for limited nest sites at low elevations, with less competitive individuals being forced to migrate to higher elevations in order to breed.

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