Lower predation risk for migratory birds at high latitudes.

Quantifying the costs and benefits of migration distance is critical to understanding the evolution of long-distance migration. In migratory birds, life history theory predicts that the potential survival costs of migrating longer distances should be balanced by benefits to lifetime reproductive success, yet quantification of these reproductive benefits in a controlled manner along a large geographical gradient is challenging. We measured a controlled effect of predation risk along a 3350-kilometer south-north gradient in the Arctic and found that nest predation risk declined more than twofold along the latitudinal gradient. These results provide evidence that birds migrating farther north may acquire reproductive benefits in the form of lower nest predation risk.

Embryonic brain growth in two shorebirds: Charadrius vociferus and Gallinago gallinago.

The sizes of six brain regions and of the whole brain were measured for a series of embryonic killdeer, Charadrius vociferus, and common snipe, Gallinago gallinago, to examine (1) the allometric relationship between whole brain and body mass through ontogeny, (2) whether the longer incubation period of the killdeer corresponds to a larger brain at hatch, (3) whether different brain regions grow independently in size through ontogeny, and (4) whether relative size of particular brain regions relates to relative importance of hatching behavior or to the relative importance of behaviors in the adult. Although snipe are generally less precocial at hatch than killdeer, and hence are predicted to have lower allometric coefficients, the allometric relationships between brain and body mass for the two species were not significantly different and were comparable to those for other birds and mammals. The onset of the rapid growth phase of the whole brain, and each region, was very early in the snipe; as a consequence, brain sizes in both species are similar at hatch, despite the shorter incubation period of snipe. In hatchlings of both species, the brain comprises about 7% of body mass. The telencephalon grows most rapidly, the diencephalon and myelencephalon grow more slowly, and the optic tectum grows steadily throughout the embryonic period. The telencephalon of the hatchling snipe is relatively larger than that of hatchling killdeer and exhibits a large nucleus basalis, typical of tactile foragers, although snipe do not forage tactily until adulthood. The relatively large optic tectum of hatchling killdeer corresponds to the highly visual method of foraging of hatchlings. However, the degree to which brain regions grow in the embryonic period, with the exception of the optic tectum and cerebellum in killdeer, appears to relate very closely to their eventual size in adults, with large brain regions growing less in the embryonic period than small brain regions.

Brain regions and encephalization in anurans: adaptation or stability?

Relative brain size and the relative size of six brain regions (main olfactory bulbs, accessory olfactory bulbs, telencephalon, optic tectum, cerebellum and brain stem) in ten species of anurans from five habitats were examined to determine whether there was any evidence of adaptation in brain structure. A previously published data set was also reanalysed. Arboreal frogs have larger body-size corrected brains than frogs from other habitats. Arboreal ranid (Platymantis vitiensis) and hylid (Hyla versicolor) possess slightly larger cerebella than the ranids and hylids from other habitats. Platymantis vitiensis lacks an accessory olfactory bulb. The fully-aquatic Xenopus laevis (Pipidae) has a smaller optic tectum and cerebellum than the non-fossorial hylids and ranids. Adaptation to life underground appears to explain the modified brains of two fossorial frogs, Hemisus guineensis (Ranidae) and Rhinophrynus dorsalis (Rhinophrynidae). Both species of fossorial frogs have reduced optic tecta, larger main olfactory and smaller accessory olfactory bulbs, and larger torus semicircularis than non-fossorial species. Our data showed a strong negative correlation between the size of the optic tectum and the size of the main olfactory bulbs. We conclude that, although anuran brains are very similar across taxa in qualitative and general structure, there are some interesting, apparent adaptations, to fossorial and arboreal life.